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Integrating a novel shape memory polymer intro surgical meshes to improve device performance during laparoscopic hernia surgery

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Title:
Integrating a novel shape memory polymer intro surgical meshes to improve device performance during laparoscopic hernia surgery
Creator:
Zimkowski, Michael M. ( author )
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
Publication Date:
Language:
English

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Subjects / Keywords:
Shape memory alloys ( lcsh )
Surgical technology ( lcsh )
Laparoscopic surgery ( lcsh )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Review:
About 600,000 hernia repair surgeries are performed each year. The use of laparoscopic minimally invasive techniques has become increasingly popular in these operations. Use of surgical mesh in hernia repair has shown lower recurrence rates compared to other repair methods. However in many procedures, placements of surgical mesh can be challenging and even complicate the procedure, potentially leading to lengthy operating times. Various techniques have been attempted to improve mesh placement, including use of specialized systems to orient the mesh into a specific shape, with limited success and acceptance. In this work, a programmed novel Shape Memory Polymer (SMP) was integrated into commercially available polyester surgical meshes to add automatic unrolling and tissue conforming functionalities, while preserving the intrinsic structural properties of the original surgical mesh. Tensile testing and Dynamic mechanical Analysis was performed on four different WSMP formulas to identify appropriate mechanical properties for surgical mesh integration. In vitro testing involved monitoring the time required for a modified surgical mesh to deploy in a 37 degrees Centigrade water bath. An acute porcine model was used to test the in vitro unrolling of SMP integrated surgical meshes. The SMP-integrated surgical meshes produced an automated, temperature activated, controlled deployment of surgical mesh on the order of several seconds, via laparoscopy in the animal model. A 30 day chronic rat model was used to test initial in vitro subcutaneous biocompatibility. To produce large more clinical relevant sizes of mesh, a mold was developed to facilitate manufacturing of SMP-integrated surgical mesh. The mold is capable of manufacturing mesh up to 361 cm, which is believed to accommodate the majority of clinical cases. Results indicate surgical mesh modified with SMP is capable of laparoscopic deployment in vivo, activated by body temperature, and possess the necessary strength and biocompatibility to function as suitable ventral hernia repair mesh, while offering a reduction in surgical operating times and improving mesh placement characteristics. Future work will include ball-burst tests similar to ASTM D3787-07, direct surgeon feedback studies, and a 30 day chronic porcine model to evaluate the SMP surgical mesh in a realistic hernia repair environment, using laparoscopic techniques for typical ventral hernia repair.
Thesis:
Thesis (Ph.D.)--University of Colorado Denver. Bioengineering
Bibliography:
Includes bibliographic references.
System Details:
System requirements: Adobe Reader.
General Note:
Department of Bioengineering
Statement of Responsibility:
by Mivchasel M. Zimkowski.

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|University of Colorado Denver
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|Auraria Library
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All applicable rights reserved by the source institution and holding location.
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892557052 ( OCLC )
ocn892557052

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Full Text
INTEGRATING A NOVEL SHAPE MEMORY POLYMER INTO SURGICAL
MESHES TO IMPROVE DEVICE PERFORMANCE DURING LAPAROSCOPIC
HERNIA SURGERY
by
MICHAEL M. ZIMKOWSKI
B.S., University of Toledo, 2005
M.S., University of Colorado Boulder, 2010
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado Denver in partial fulfillment
of the requirement for the degree of
Doctor of Philosophy
Bioengineering
2013


This thesis for the Doctor of Philosophy degree by
Michael M. Zimkowski
has been approved for the
Department of Bioengineering
by
Kendall Hunter, Chair
Robin Shandas, Advisor
Daewon Park
Mark E. Rentschler
Jonathan Schoen
November 14, 2013
11


Zimkowski, Michael M. (Ph.D., Bioengineering)
Integrating a Novel Shape Memory Polymer into Surgical Meshes To Improve Device
Performance During Laparoscopic Hernia Surgery
Thesis directed by Professor Robin Shandas.
ABSTRACT
About 600,000 hernia repair surgeries are performed each year. The use of laparoscopic
minimally invasive techniques has become increasingly popular in these operations. Use
of surgical mesh in hernia repair has shown lower recurrence rates compared to other
repair methods. However in many procedures, placement of surgical mesh can be
challenging and even complicate the procedure, potentially leading to lengthy operating
times. Various techniques have been attempted to improve mesh placement, including
use of specialized systems to orient the mesh into a specific shape, with limited success
and acceptance. In this work, a programmed novel Shape Memory Polymer (SMP) was
integrated into commercially available polyester surgical meshes to add automatic
unrolling and tissue conforming functionalities, while preserving the intrinsic structural
properties of the original surgical mesh. Tensile testing and Dynamic Mechanical
Analysis was performed on four different SMP formulas to identify appropriate
mechanical properties for surgical mesh integration. In vitro testing involved monitoring
the time required for a modified surgical mesh to deploy in a 37C water bath. An acute
porcine model was used to test the in vivo unrolling of SMP integrated surgical meshes.
The SMP-integrated surgical meshes produced an automated, temperature activated,
controlled deployment of surgical mesh on the order of several seconds, via laparoscopy
in the animal model. A 30 day chronic rat model was used to test initial in vivo
subcutaneous biocompatibility. To produce large more clinical relevant sizes of mesh, a
iii


mold was developed to facilitate manufacturing of SMP-integrated surgical mesh. The
mold is capable of manufacturing mesh up to 361 cm2, which is believed to accommodate
the majority of clinical cases. Results indicate surgical mesh modified with SMP is
capable of laparoscopic deployment in vivo, activated by body temperature, and
possesses the necessary strength and biocompatibility to function as suitable ventral
hernia repair mesh, while offering a reduction in surgical operating time and improving
mesh placement characteristics. Future work will include ball-burst tests similar to
ASTM D3787-07, direct surgeon feedback studies, and a 30 day chronic porcine model
to evaluate the SMP surgical mesh in a realistic hernia repair environment, using
laparoscopic techniques for typical ventral hernia repair.
The form and content of this abstract are approved. I recommend its publication.
Approved: Robin Shandas
iv


ACKNOWLEDGEMENTS
I would like to give special thanks to Professor Robin Shandas for his incredible direction
and guidance, Dr. Jonathan Schoen, Professor Kendall Hunter, Professor Mark
Rentschler and Professor Daewon Park for serving on my committee. I would also like to
thank Dr. Nageswara Mandava for initial concepts and input related to the medical device
discussed in this dissertation.


CONTENTS
Chapter
1 Introduction..............................................................1
2 Background and Motivation.................................................4
2.1 Surgical Methods......................................................5
2.1.1 Laparoscopic Intra-Peritoneal Prosthetic Patch (LIPP) Approach...6
2.1.2 Trans Abdominal Pre-Peritoneal (TAPP) Laparoscopic Approach......6
2.1.3 Totally Extra Peritoneal (TEP) Laparoscopic Approach..............7
2.1.4 Open Hernia Repair................................................8
2.2 Conventional Repair Options...........................................9
2.2.1 Polypropylene Mesh................................................9
2.2.2 Polyester (polyethylene terephthalate) Mesh......................10
2.2.3 Expanded polytetrafluoroethylene (ePTFE).........................10
2.3 Existing Mesh Placement Options......................................11
2.3.1 Traditional Mesh Placement Technique.............................11
2.3.2 Bard Echo PS Positioning System.................................12
2.3.3 Covidien AccuMesh Positioning System.............................13
2.4 Proposed Shape Memory Polymer System.................................14
3 Stage 1 Device Development: Synthesis and In Vitro Testing................15
3.1 Chemistry............................................................15
3.2 Synthesis............................................................18
3.3 Dynamic Mechanical Analysis..........................................19
vi


3.4
Uniaxial Tensile Tests
19
3.5 Time to Unroll in Water..............................................20
3.6 Moi sture Ab sorption................................................21
3.7 Cytotoxicity Study...................................................22
4 In vivo Animal Testing..................................................23
4.1 Synthesis............................................................23
4.2 Acute Porcine Studies................................................24
4.2.1 Stage 1 Porcine Studies..........................................25
4.2.2 Stage 2 Porcine Studies..........................................26
4.3 Chronic Rat Studies..................................................26
5 Experimental Results......................................................29
5.1 Dynamic Mechanical Analysis..........................................29
5.2 Uniaxial Tensile Tests...............................................31
5.3 Time to Unroll in Water..............................................34
5.4 Cytotoxicity Study...................................................35
5.5 Moi sture Ab sorption................................................36
5.6 Acute Porcine Studies................................................36
5.6.1 Stage 1 Porcine Studies..........................................36
5.6.2 Stage 2 Porcine Studies..........................................38
5.7 Chronic Rat Studies..................................................40
6 Manufacturing Mold Development..........................................44
44
vii
6.1 Mold Design.......
6.2 UV-Polymerization
47


6.3 Post-Polymerization Annealing.......................................49
6.4 Sterilization.......................................................50
6.5 Sample Verification.................................................50
7 Discussion...............................................................52
8 Future Directions........................................................57
8.1 Mechanical Studies..................................................57
8.2 Direct Surgeon Feedback Studies.....................................59
8.3 Large Animal Studies................................................60
9 Conclusion...............................................................61
Bibliography..................................................................62
References....................................................................63
Appendix
A. Tables.....................................................................69
viii


LIST OF TABLES
Table
1 - Chemical Structure of Primary Components...................................16
2 - SMP Polymerization Chemistry...............................................17
3 Polymer Networks Tested.....................................................18
4 -Polymer Networks for Cytotoxicity Testing...................................18
5 - Selected Tensile Test Results..............................................32
6 Cytotoxicity Results........................................................35
7 - List of all polymer solutions prepared.....................................69
8 - Tensile results for all networks tested....................................69
IX


LIST OF FIGURES
Figure
1 Trans Abdominal Pre-Peritoneal (TAPP) Laparoscopic repair method [A].............7
2 Total Extra Peritoneal (TEP) laparoscopic repair method [1]......................8
3 - Bard Echo PS Positioning System, with inflation balloon (green) attached to mesh
(white) [B].........................................................................13
4 - Covidien AccuMesh Positioning System [C].....................................14
5 - (a) Dynamic Mechanical Analysis diagram (b) Uniaxial Tensile Test diagram.......20
6 - Time to unroll test procedure..................................................21
7 - (A) unmodified mesh; (B) SMP coated porous polyester surgical mesh..............24
8 - Non-porous SMP modified polyester surgical mesh................................24
9 - (a) abdominal wall defect is created; (b) repaired with implanted surgical mesh.28
10 - Dynamic Mechanical Analysis (DMA) of formulas tested, (a) Formula A, Tg=57C;
(b) Formula B, Tg=37C; (c) Formula C, Tg=47C; (d) Formula D, Tg=44C...............30
11 - Formula F SMP/SMP-Mesh characteristics: a) SMP alone shows Tg = 41C; b)
SMP+Mesh tested in lengthwise direction shows Tg = 40C; c) SMP+Mesh tested in
widthwise direction shows Tg = 38. Indicates mesh has minimal effect on native SMP
Tg characteristics..................................................................31
12 - Strain to Failure of SMP alone; Formula C and D show superior Tg and strain-to-
failure.............................................................................33
13 - No statistical difference is observed between the SMP modified mesh and the control


14 - Demonstration of unrolling (top panel) and time to unroll (bottom panel) for each of
the formulas, in 37C water bath. As Tg decreases, time to unroll also decreases....35
15 Moisture Absorption of Formula F...............................................36
16 - Significant laparoscopic manipulation was required to facilitate unrolling of the C
PET-SMP surgical mesh within 150 seconds time (Tg = 47C)...........................37
17 - Significantly less laparoscopic manipulation was required to unroll the Formula D
PET-SMP surgical mesh (Tg = 44C)...................................................38
18 - Non-Porous fully coated SMP-mesh automatically unrolls after 25 seconds as the
sample reaches body temperature....................................................39
19 - Porous SMP-mesh automatically unrolls after 31 seconds as the sample reaches body
temperature........................................................................40
20 - Abdominal view of a shaved rat 30 days post-op; red arrows (left) indicate
unmodified (control) mesh suture locations and blue arrows (right) indicate SMP-mesh
(experimental) suture locations....................................................41
21 - Unmodified control mesh tissue ingrowth. Inflammatory response is as expected,
demonstrating tissue ingrowth into polyester fibers and mesh pores..................41
22 - SMP-modified mesh demonstrates similar tissue ingrowth characteristics........42
23 Picrosirius red stain displays collagen (red) integration into unmodified mesh.43
24 Picrosirius red stain displays collage (red) integration into SMP-modified mesh 43
25 - Mold with Mesh Sample........................................................45
26 - Mold Cross-Section...........................................................45
27 - Manufacturing Mold with Polymer Solution Well................................46
28 - Single Source UV Polymerization Setup.........................................48
xi


29 Dual Source UV Polymerization Setup...................................49
30 - Formula F made using original technique compared to Formula F manufactured with
new mold...................................................................51
31 - Tissue ingrowth of: Unmodified mesh (top), with collagen fibers extending between
PET fibers and through mesh pores. SMP-modified mesh (bottom), with collagen fibers
extending through mesh pores only. SMP coating prevents thick scar formation.54
Xll


LIST OF ABBREVIATIONS
DMA Dynamic Mechanical Analysis
ePTFE expanded polytetrafluorethylene
FBGC foreign body giant cell
FDA Food and Drug Administration
IACUC Institutional Animal Care and Use Committee
PET polyethylene terephthalate (commonly called polyester)
SMP Shape Memory Polymer
TAPP Trans Abdominal Pre-Peritoneal
TEP Total Extra Peritoneal laparoscopic approach
Tg Glass Transition Temperature (or Activation Temperature)
UV ultra-violet


1 Introduction
Hernia repair surgery is one of the more common surgical procedures, with more
than 600,000 hernia repair operations performed annually in the United States [1], Hernia
repair often involves abdominal wall tissue reinforcement as it is widely accepted to
reduce hernia recurrence rates. Minimally invasive laparoscopic surgery has become
increasingly popular in recent years and is often used to decrease surgical trauma and
recovery time, including in hernia repair procedures [2],[1], Synthetic meshes have
become popular as a tissue reinforcement material in both open and laparoscopic
procedures because these materials provide flexibility and strength. Newer meshes may
also include absorbable and composite types. Absorbable meshes are designed to break
down over time, eventually being replaced with natural tissue. Composite types combine
two materials, such as synthetic material and an absorbable material.
Many laparotomies performed each year involve incisional/ventral hernias, where
reinforcing mesh can be challenging for the surgeon to position. Despite the challenges of
mesh, surgical outcomes has confirmed that reduced morbidity and lower recurrence
rates can be achieved by reinforcing the tissue with a surgical mesh [3],
As mentioned, in many laparoscopic hernia repair procedures the placement of
surgical mesh can present a challenge and even complicated the procedure [4], The
surgical mesh must be rolled and folded into a cannula port, inserted into an abdominal
port and released near the abdominal area to be repaired. Once in the abdominal cavity,
the surgical mesh must be unrolled, formed to fit the anatomy and attached with sutures


or a variety of other means. Unrolling and tamping of the surgical mesh can require
significant amounts of time, which may increase surgical complications such as
recurrence, infection or pain.
Various techniques have been attempted to make mesh placement easier, including
the introduction of a shape memory functionality. One of example of this has been the
use of specialized geometry or manufacturing reinforcement rings to push mesh into a
specific shape, all of which have had limited success [5], Perhaps the most well-known
example is the Davol Bard Composix Kugel patch, which was voluntarily recalled
due to risk of breakage resulting in potentially dangerous complications [6], This patch
incorporated a stiff polymer which must be bent to accommodate the cannula port and
then is released into the abdominal cavity wherein elastic memory snapped the mesh into
place. Reports of patient injury began to surface in 2002 and problems ultimately led to a
series of FDA recalls from 2005 to 2007 [6], The cause of failure was eventually traced
to a weld of the polyethylene terephthalate (PET commonly called polyester) ring [6],
The weld can break, causing the stiff wire to protrude from the repair site, resulting in
fistula or other serious complications [6], Another example of a similar product is the
Davol Bard Polysoft surgical mesh, which also utilizes a polyester/PET ring inside a
polypropylene mesh [7], Products of this nature utilize elastic memory to snap the
hernia mesh into position, an intrinsically dangerous process since the deployment is
uncontrolled.
A shape memory polymer (SMP) can be used to obtain controlled deployment. A
SMP is a classification of polymers that provide tailorable mechanical functionalities, are
2


capable of active movement into pre-programmed shapes, and can be compressed into a
small shape and later unfolded into a functional shape using a trigger, such as
temperature [8],[9], SMPs have gained increased notice over the past several years as
potential biomaterials for minimally invasive surgical devices [8],[9], They have already
been used in orthopedic, cardiovascular and ophthalmic applications, showing good
biocompatibility and tissue in-growth [8], This work introduces a novel thermally
activated SMP, which can be applied to commercially available surgical meshes using an
ultra-violet (UV) polymerization process.
3


2 Background and Motivation
A hernia is defined as a protrusion or projection of an organ or part of an organ
through the wall of the cavity that normally contains it [3], Hernia repair often involves
tissue reinforcement. The development of abdominal wall reinforcements can be traced
back to 1894, when Phelps introduced the concept of using a silver wire coil on the floor
of the inguinal canal [3], In the more modern age, stainless steel was used to form wire
rings for use as reinforcements, but these systems were plagued with reports of
fragmentation and erosion into abdominal structures [3], As polymers became more
popular as biomaterials, their use as a reinforcement mesh became a natural step due to
the increased flexibility compared to metal ring predecessors. Polymeric materials have
included regenerated cellulose (Fortisan), polyvinyl alcohol (Ivalon), nylon, acrylic
cloth (Orion), fiberglass, polyester sheeting (Mylar), polytetrafluoroethylene (Teflon)
and carbon fiber [3], When used in hernia repairs, many of these materials led to
disintegration, rejection and required additional surgery for removal.
The modern era of hernia repair is often considered to have begun in 1958 when
Francis Cowgill Usher published landmark experiences on fascia reinforcement and
replacement biomaterials and worked with engineers to develop an optimal, novel hernia
repair material polypropylene mesh, which showed great success in animals [3], From
his work, the three main types of modern meshes were introduced: derivatives of
polypropylene; polyester; and expanded polytetrafluorethylene (ePTFE) [3], Many newer
types of meshes also combine absorbable, non-absorbable and composite materials.
Absorbable meshes are designed to break down over time, and are comprised of
4


resorbable materials like polyglycolic acid (PGA) or collagen. Composite meshes also
exist, such as combining ePTFE and polypropylene, or polyester and PGA. The later
would be considered a partially absorbable composite mesh, using a synthetic material
for strength and resorbable material to aid in tissue integration. Examples of partially
absorbable meshes include Ethicon UltraPro (polypropylene and PGA) and Covidien
Parietex optimized composite mesh (polyester and collagen film).
As previously noted, minimally invasive laparoscopic surgery has become
increasingly popular in recent years and is often used to decrease surgical trauma and
recovery time, including in hernia repair procedures [2],[1], In the United States, 4 to 5
million laparotomies are performed annually; approximately 20% of these involve
incisional/ventral hernias (-400,000 to 500,000 / year) [10], Evaluating post laparoscopic
surgery outcomes has confirmed that significantly reduced morbidity and lower
recurrence rates can be achieved by reinforcing the tissue with a surgical mesh [3], A 10-
year follow-up showed the cumulative rate of recurrence was 63% for suture only repair
and 32% for repairs including mesh [10], In patients with small incisional hernias, the
recurrence rate was 67% with a suture repair and 17% with a repair including mesh [10],
Clearly, the use of mesh and laparoscopic techniques has made an important impact in
reducing recurrence and surgical complications of hernia repair procedures.
2.1 Surgical Methods
Common surgical methods used to repair hernias included the Trans Abdominal Pre-
Peritoneal laparoscopic approach, the Total Extra Peritoneal laparoscopic approach, and
5


the traditional open repair method. These methods are described in further detail in the
following sections.
2.1.1 Laparoscopic Intra-Peritoneal Prosthetic Patch (LIPP) Approach
The Intra-Peritoneal laparoscopic repair method is the primary procedure used for ventral
hernia repair, has been well documented [11], [12], This is the primary method
referenced in this dissertation. The hernia repair is performed in a space created between
the peritoneum and the intestines, leaving the peritoneum attached to the abdominal wall.
An endoscope is inserted into the peritoneal cavity, which is then insufflated to separate
the peritoneum from the internal organs, creating a working space which is
intraoperatively maintained with insufflation through laparoscopic ports. The hernia sac
and any abdominal wall adhesions are dissected, and an appropriate sized mesh is chosen
to overlap the hernia defect. The mesh is then tacked and sutured to the abdominal wall to
cover the defect. Anteriorly the mesh is in contact with peritoneum and muscle wall and
posteriorly the mesh is in contact with the intestines. As the inflammatory process
proceeds during healing, this direct contact between mesh and bowel can lead to
adhesions, making mesh design an important consideration.
2.1.2 Trans Abdominal Pre-Peritoneal (TAPP) Laparoscopic Approach
In the Trans Abdominal Pre-Peritoneal (TAPP) laparoscopic repair method, the
hernia repair is performed in a space created between the peritoneum and the intestines.
An endoscope is inserted into the pre-peritoneal space, which is then insufflated to
separate the peritoneum from the internal organs, creating a working space which is
6


intraoperatively maintained with insufflation through laparoscopic ports. Abdominal
wall adhesions are divided and the hernia sac is reduced. The peritoneum is dissected to
reveal the defect, which is to be repaired with hernia mesh. Appropriate sized mesh is
chosen to allow overlap with the defect, and it is fixed to the abdominal wall with tacks
and sutures. Peritoneal flaps are then sutured back together, placing the peritoneum
between the mesh and the intestines, which acts as barrier to prevent adhesions. This is a
common repair approach in inguinal hernia repair procedures [13], but recent studies
have shown this as an option for ventral hernia procedures as well [14], An illustration of
the TAPP approach is shown in Figure 1.
Figure 1 Trans Abdominal Pre-Peritoneal (TAPP) Laparoscopic repair method [A]
2.1.3 Totally Extra Peritoneal (TEP) Laparoscopic Approach
The primary difference of the Total Extra Peritoneal (TEP) laparoscopic repair
method is that the hernia repair is performed in a space created between the muscle wall
and the peritoneum. An endoscope with balloon is inserted into the peritoneal space,
which is then inflated to separate the peritoneum from the interior muscle wall, creating a
7


pre-peritoneal working space which is intraoperatively maintained with insufflation. The
hernia sac is dissected and the defect is repaired with hernia mesh similar to the TAPP
procedure. This method does not disturb the peritoneum and does not require entering
the intra-peritoneal space. This is a common repair approach in inguinal hernia repairs
[13], An illustration the TEP approach is shown in Figure 2.
Peritoneum
Endoscope with balloon in
preperitoneal space
Endoscope with balloon advanced
interiorly in preperitoneal space^
Peritoneum
Pubis
Bladder
Expanded preperitoneal space
maintained with insufflation
Figure from Sabiston Textbook
of Surgery, 18th Ed, Pgll67
Figure 2 Total Extra Peritoneal (TEP) laparoscopic repair method [1]
2.1.4 Open Hernia Repair
Open hernia repair is performed by making an incision to dissect through the
subcutaneous tissues and fascia. The external muscles and other local anatomy are
8


identified and the dissection continues until the hernia sac is identified. The hernia sac is
dissected away from any adjacent structures and examined for contents. Contents, such
as intestine, are inserted back into the peritoneal space. A piece of synthetic mesh is cut
to fit the defect, ensuring a 5-6 cm boarder overlap with tissue surrounding the defect.
The mesh may be secured using sutures or tacks, or a combination of the two, however
many surgeons rely on intra-abdominal pressure alone to hold the mesh in place [1], [15],
[16].
2.2 Conventional Repair Options
Evaluations of post-laparoscopic surgery outcomes has confirmed that significantly
reduced morbidity and lower recurrence rates can be achieved by reinforcing the tissue
with a surgical mesh [3], A 10-year follow-up showed the cumulative rate of recurrence
was 63% for suture only repair and 32% for repairs including mesh [10], In patients with
small incisional hernias, the recurrence rate was 67% with a suture repair and 17% with a
repair including mesh [10], Due to these results, suture-only repairs have been largely
abandoned. Clearly, the use of mesh and laparoscopic techniques has made an important
impact in reducing recurrence and surgical complications of hernia repair procedures.
2.2.1 Polypropylene Mesh
The use of polypropylene mesh was first introduced by Usher in 1963 [17], It saw
some success, but in 1989 Lichtenstein introduced the tension-free repair, using
polypropylene mesh, which showed excellent results [18], Atension-free repair
involves using mesh to strengthen the defect, without suturing the sides of the defect


together, thereby eliminating tension in the adjacent muscles. This surgical approach has
since become the preferred method of treatment, making polypropylene into one of the
most common mesh materials in the United States of America. Examples of
polypropylene mesh common in the hernia repair marketplace include Marlex (C.R.
Bard/Davol, Inc), Prolene (Ethicon, Inc) and Parietene (Covidien Ltd).
2.2.2 Polyester (polyethylene terephthalate) Mesh
The use of polyester mesh was introduced as a competitor to polypropylene. It has
been used in similar indications as polypropylene mesh. Some data published during
from the 1980s to 1990s suggested that polyester had higher infection rates compared to
polypropylene [19], However, more recently studies have shown polyester to be safe for
hernia repairs [20], In fact, because polyester is a more pliable material with good
strength, recent studies demonstrate that it may be more appropriate than polypropylene
for hernia repairs [21], [22], As a result, polyester has become the preferred material in
Europe and has surpassed polypropylene. Examples of polyester mesh common in the
hernia repair marketplace include Mersilene (Ethicon, Inc) and Parietex (Covidien
Ltd).
2.2.3 Expanded polytetrafluoroethylene (ePTFE)
The use of expanded polytetrafluorethylene (ePTFE) was introduced as a competitor
to both polyester and polypropylene. It is also been used in similar indications as the
other two materials. ePTFE meshes, like those offered by Gore Medical, have
significantly smaller pore sizes, which prevent tissue adhesion, so they are often used in
10


applications where bowel adhesion and the risk of fistula is of concern. Unfortunately,
the small pores which prevent tissue adhesion also prevent immune cells from fighting
infections which may arise in ePTFE meshes [23], Examples of ePTFE mesh common in
the hernia repair marketplace include Dulex (C.R. Bard/Davol, Inc), DualMesh (W.
L. Gore & Associates), and Parietex Composite (Covidien Ltd).
2.3 Existing Mesh Placement Options
Surgical mesh placement during ventral hernia repair continues to present a
challenge to many surgeons. Traditional laparoscopic placement techniques involve
marking the mesh, using orientation sutures and unfolding the mesh systematically in
vivo. Two systems are currently available to aid in mesh placement the Bard Echo PS
Positioning System, and the Covidien AccuMesh Positioning System.
2.3.1 Traditional Mesh Placement Technique
Traditional laparoscopic ventral hernia repair starts with port insertion. Typically,
this repair involves the use of three ports, however additional ports may be inserted if
necessary. Generally, a camera port is placed laterally in the upper left or right quadrant
of the abdomen. Additional tool ports are generally placed in as far apart laterally as
possible. The ventral hernia defect is identified, and the contents are dissected away from
the hernia sac. Internally, the defect is measured using a sterile ruler, or externally the
defect is measured by probing with a spinal needle. When measuring externally, a marker
is used to draw the outline of the defect on the skin. Once the defect size has been
determined, a mesh of the appropriate size is chosen to provide approximately 5 cm of
11


overlap with healthy tissue. If necessary, the mesh is cut to fit. An orientation suture is
placed in the center of the mesh, and additional lateral orientation sutures may also be
attached to the mesh before insertion. A marker may also be used to identify anatomical
orientation. The mesh is then rolled lengthwise and inserted through the largest
laparoscopic port. After insertion into the abdominal cavity, the mesh is unrolled and
manipulated into position so that the orientation sutures face anteriorly toward the defect.
A suture passer is inserted through the abdominal wall from the outside, used to grasp the
orientation sutures and raise the mesh into position over the defect. Alternatively, a
mechanical fixation device utilizing tacks may be used to secure the mesh against the
inside of the abdominal wall. Once fixed to the abdominal wall, the laparoscopic cavity
can be deflated and the wounds can be closed.
2.3.2 Bard Echo PS Positioning System
The steps of mesh placement are similar to the traditional technique, but modified for
the use of the Bard Echo PS Positioning System. This system is designed for
laparoscopic placement of their Ventralight ST or Composix L/P mesh. It utilizes a
balloon scaffold system attached to the mesh, which is inflated in vivo for mesh
placement, and later removed. The mesh and balloon are pre-packaged in tight roll inside
an introducer tool. The introducer tool is centered over the defect site to facilitate mesh
placement and defect repair, eliminating the need for orienting sutures. This device
however requires extra steps to deflate the balloon and remove the balloon scaffold,
making this a potentially cumbersome solution to mesh placement. The Bard Echo PS
system is shown in Figure 3.
12


Inflation line
www.davol.com
Figure 3 Bard Echo PS Positioning System, with inflation balloon (green) attached to
mesh (white) [B]
2.3.3 Covidien AccuMesh Positioning System
The Covidien AccuMesh Positioning System is designed for laparoscopic
placement of the Covidien Parietex Optimized Composite Mesh. This positioning
system uses a complicated mechanically expanding frame to facilitate mesh placement.
The frame and mesh are inserted through a laparoscopic port in a compact form using a
deployment tool. Inside the abdominal cavity, the frame is actuated using levers and
sliders on the deployment tool to unroll the mesh and position it over the defect. The
multitude of complex mechanical moving parts inherently makes this system prone to
problems. The Covidien AccuMesh system is shown in Figure 4.
13


Figure 4 Covidien AccuMesh Positioning System [C]
2.4 Proposed Shape Memory Polymer System
The aim of this work was to develop a SMP formula that could be integrated into
surgical mesh and provide the capability of laparoscopic deployment, with unassisted in
vivo unrolling. SMPs are defined by the ability to recover large deformations from a
storage state in response to an environmental stimulus [8], which may be beneficial for a
hernia mesh application. Design criteria for the SMP to be integrated into surgical mesh
required an ability to activate upon exposure to body temperature with high strain-to-
failure while imposing minimal change on the native mechanical strength of the mesh.
Several SMP formulas were evaluated using the following tests: uniaxial tensile tests,
dynamic mechanical analysis, and measurement of time-to-unroll. Using these tests, SMP
formulas were identified which showed useful glass transition temperature (Tg) and
higher strain-to-failure. A SMP formula with a Tg around body temperature is most
useful in this application. These SMP formulas were then tested in vivo using a porcine
model to evaluate efficacy of laparoscopic deployment and unassisted unrolling.
14


3 Stage 1 Device Development: Synthesis and In Vitro Testing
Creating the modified surgical mesh specimens was accomplished by integrating the
novel shape memory polymer (SMP) into a commercially available polyester mesh
(PETKM14001 or PETKM7001, Textile Development Associates). Modified and
unmodified surgical meshes were evaluated using dynamic mechanical analysis, tensile
strength, time to unroll and cytotoxicity tests.
3.1 Chemistry
Chemicals tert-Butyl acrylate (tBA), poly(ethylene glycol) dimethacrylate
(PEGDMA), 2,2-dimethoxy-2-phenylacetophenone (DMPA) photo-initiator, and other
polymer components were combined to create multiple polymer solutions. Chemical
structures of the three primary components are shown in Table 1. A complete list of
polymer solutions is shown in Appendix A, Table 7.
15


Table 1 Chemical Structure of Primary Components
Component Structure
PEGDMA v O CM X ch3 'o^-'y^ch2 n 0
tBA 0 ch3 CH3 ch3
DMPA (initiator) 0 och3 -och3
SMP creation proceeds by reacting networks of initiator, backbone and cross-linkers
together. The reaction occurs by free-radical polymerization initiated by ultra-violet (UV)
radiation. UV cleaves the bonds of the initiator DMPA homolytically, creating free-
radicals that attack vinyl groups (carbon-carbon double bonds) of the backbone and
cross-linker. Backbone and cross-linker connect together in a random network, and
finally the reaction terminates as all radicals have been reacted. This reaction is
demonstrated in Table 2.
16


17


3.2 Synthesis
Polymer synthesis for each test was performed using a free radical UV-
polymerization process. Specific parameters are described below for each phase of
synthesis.
For initial DMA, Tensile and Time-to-Unroll testing, four polymer solutions were
selected for testing and prepared as shown in Table 3. A complete list of polymer
networks tested is shown in Appendix A, Table 7.
Table 3 Polymer Networks Tested
tBA (wt%) nBA (wt%) PEGDMA (wt%)
Formula A 80 0 20 (Mn = 550)
Formula B 65 15 20 (Mn = 550)
Formula C 75 10 15 (Mn = 550)
Formula D 80 0 20 (Mn = 1000)
For cytotoxicity testing, three polymer solutions were selected for testing and
prepared as shown in Table 4.
Table 4 -Polymer Networks for Cytotoxicity Testing
tBA (wt%) iBA (wt%) EHA (wt%) PEGDMA (wt%)
Formula F 78 0 0 22 (Mn = 1000)
Formula M 79 0 2 19 (Mn= 1000)
Formula P 79 2 0 19 (Mn= 1000)
Polymer solution was applied to commercially available surgical meshes using a free
radical UV-polymerization process. Similar combinations have been previously
described by our group [8],[24], Surgical meshes were placed in glass molds (75 mm by
25 mm) in a flat configuration, and SMP solution was injected. The molds were then
18


placed under a 365nm UV lamp (Model B100AP; Black-Ray) for 10 minutes for photo-
curing.
3.3 Dynamic Mechanical Analysis
Dynamic Mechanical Analysis (DMA) was performed in tensile loading to
determine glass transition temperature (Tg) and storage modulus of all SMP
formulations. A graphical representation of the DMA test is shown in Figure 5a. Using
Formula F, an additional DMA study was performed using samples of SMP alone and
with non-porous SMP-integrated mesh in both the lengthwise and widthwise directions to
evaluate any potential change in Tg resulting from the SMP-mesh composite formulation.
All samples were cut to approximately 25 mm long x 5.5 mm wide x 1 mm thick, and
DMA was performed using a TA Q800 DMA. The samples were thermally equilibrated
at 0C for 5 minutes and then heated to 100C at a rate of 3C per minute. Testing was
performed in cyclic strain control at 0.1% strain and at a frequency of 1.0 Hz. A preload
force of 0.01N and a force track setting of 125% were used. Tg was defined at the peak of
the tan delta curve.
3.4 Uniaxial Tensile Tests
SMP formulas alone, unmodified mesh materials and modified mesh materials with
integrated SMP were tested. Uniaxial tensile tests were based upon ASTM Test Method
D638-03, using Type V specimen geometry. This test procedure was similar to that
outlined by Deeken et al. in 2011 [12], Specimens measuring approximately 9.5 mm x
63.5 mm x 1 mm were cut using a D638-03 Type-V cast steel die (North East Cutting Die
19


Corp., Portsmouth, NH). A graphical representation of the uniaxial tensile test is shown
in Figure 5b.
A
Test .
Sample
Fixed
Upper Grip
Tensile
Force
1
Aqueous
environment
at 37C
Upper Grip
Moving
Lower
Grip
D638-V
Sample
Cyclic
Load Applied
Fixed
Lower Grip
Figure 5 (a) Dynamic Mechanical Analysis diagram (b) Uniaxial Tensile Test
diagram
Tensile tests were performed using an Insight 5SL test machine (MTS, Eden Prairie,
MN), in an aqueous environmental chamber at 37C with the specimen immersed in
deionized water, using a tension rate of 5 mm/min.
3.5 Time to Unroll in Water
Developing a useful shape memory polymer for deploying a surgical mesh
necessitates in vivo unrolling within a reasonable time, however the mesh should not
unroll readily at typical operating room temperatures. The amount of time required for
modified meshes to unroll was evaluated to determine the impact of adding shape
memory polymer, as a function of temperature, similar to protocols previously described
[9], [13], [14], SMP modified mesh specimens approximately 75 mm by 25 mm were
20


prepared as previously described. Each specimen was heated using hot water (>65C) to
bring the sample into the rubbery region. The sample was rolled tightly by hand and
cooled using cold water (< 7C) to bring the sample into the glassy region to retain the
rolled configuration. Using soft tipped forceps, each rolled mesh formula was
individually deployed into a deionized water bath held at approximately 37C, to
simulate introduction into a wet surgical environment. The elapsed time for unassisted
unrolling was recorded by video. A schematic of this process is shown in Figure 6.
SMP
unrolls
37C
Cooled SMP
Retains shape
Figure 6 Time to unroll test procedure
3.6 Moisture Absorption
Moisture absorption was measured using a submersion method at three different
temperatures. A total of nine samples were submerged in IX Phosphate Buffer Solution
(PBS): three samples at room temperature, three samples at 37C, and three samples at
70C. These temperatures test in the glassy region, body temperature and the rubbery
21


region of the SMP. Each sample was weighed before submersion, and again at 24 hours,
48 hours, and 96 hours after submersion. The percentage of weight change is reported.
3.7 Cytotoxicity Study
Cytotoxicity testing was performed by WuXi AppTec, Inc (St. Paul, MN) using a
MEM elution method compliant with ISO 10993-5:2009. Non-porous SMP-meshes
utilizing Formula F, M and P were used in this test to maximize sample exposure and
sterilized by autoclave. The test consists of an extraction process, an exposure process
and experimental evaluation. The elution consists of placing 30 cm2 of SMP-mesh
sample in 10 mL of Eagles MEM +5% fetal bovine serum. The sample was extracted at
37 C for 24 hours. The media was then inoculated into a L-929 mouse fibroblast cell line
and the cells are incubated at 37 C. Cultures were evaluated for cytotoxic effects by
microscopic observation at 24, 48 and 72 hour incubation periods.
Criteria for evaluating cytotoxicity included morphologic changes in cells, such as
granulation, crenation, or rounding, and loss of viable cells from the monolayer by lysis
or detachment. Evaluation scoring was performed according to the ISO standards,
wherein test results ofO, 1 or 2 are considered non-toxic and results of3 or 4 are
considered toxic.
22


4 In vivo Animal Testing
Unrolling behavior of modified surgical meshes was evaluated using in an acute
porcine model and chronic biocompatibility was evaluated using a rat model.
Experiments were conducted under test protocols approved by the Institutional Animal
Care and Use Committee (IACUC Protocol # 87912(04)1D and # 43812(08)1D).
4.1 Synthesis
Polymer solution was applied to commercially available surgical meshes using UV-
polymerization. Similar SMP combinations and shape memory polymer surgical meshes
have been previously described by our group [25], [26], Surgical meshes were placed in
glass molds (100 mm by 100 mm) in a flat configuration and SMP solution was injected
and subsequently cured using a Dymax 2000-PC ultraviolet lamp. Non-porous SMP
modified meshes were created by filling the mold with SMP, resulting in a mesh
embedded in SMP. Porous SMP modified meshes were created by first purging the mold
with nitrogen gas, injecting enough SMP solution to coat the mesh fibers, and continually
purging the mold with nitrogen gas during polymerization process to prevent oxygen
inhibition. Excellent retention of the original pore size of the unmodified mesh was
obtained using this process. A photomicrograph comparing an unmodified mesh with a
porous SMP-mesh is shown in Figure 7. A photomicrograph of a non-porous SMP
modified mesh is shown in Figure 8.
23


4.2 Acute Porcine Studies
This study was conducted under a test protocol approved by the Institutional Animal
Care and Use Committee (IACUC protocol #87912(04)1D), and was performed in live
female pigs weighing approximately 100 lbs. Each swine was anesthetized using
ketamine and xylazine for induction and isoflurane for maintenance, and secured in a
supine position. Several laparoscopic ports were inserted to perform experiments within
24


the abdominal cavity. At the completion of testing, the animal was euthanized by
anesthesia overdose. Formula C and D were chosen for the acute swine model test due to
characteristics identified in tensile and DMA testing (Chapter 3). Surgical meshes were
placed in glass molds (100 mm by 100 mm) in a flat configuration, and SMP solution
was injected, and subsequently cured using UV energy to create non-porous SMP-
integrated meshes. After synthesis, modified and unmodified surgical mesh specimens
were cut to approximately 70mm x 70mm to ensure uniform shape and size. Formula C
specimen had a thickness of 0.68 mm, and Formula D specimen had a thickness of 1.0
mm. Final specimens were steam sterilized by a standard autoclave system.
4.2.1 Stage 1 Porcine Studies
The surgical procedure consisted of placing two SMP modified meshes (Formula C
and D) against the porcine abdominal wall using standard intraperitoneal laparoscopic
approach. Intra-abdominal cavity temperature was monitored before insertion of each
mesh using a thermometer (HH506RA, Omega). No peritoneal defect was created in this
study. Modified surgical meshes were submerged in sterile water heated to 50C, rolled
to fit into a cannula port and cooled by submerging in sterile water cooled to less than
20C. The SMP modified meshes retained the rolled shape, and were inserted into the
abdominal cavity of the swine using a 12mm laparoscopic cannula port. The surgeon (Dr.
Schoen) positioned the modified mesh on the intestines, and awaited automated unrolling
as the temperature of the modified mesh increased to that of the abdominal cavity. Both
meshes were then secured using 5mm tacks (Protack, Covidien) at four corners to
evaluate feasibility of tack usage with added thickness of SMP. The thicker Formula D
25


modified mesh was punctured twice using a suture grasper (Proxy Biomedical) to
evaluate feasibility of penetration properties.
4.2.2 Stage 2 Porcine Studies
In the second stage of porcine studies, the surgical procedure consisted of placing
three hernia meshes approximately 80 mm x 80 mm in size (fully SMP coated, porous
SMP coated, and unmodified) were placed against the porcine abdominal wall using an
intraperitoneal laparoscopic approach. No peritoneal defect was created in this study.
Modified surgical meshes were submerged in water heated to approximately 50C, rolled
to fit into a cannula port and cooled by submerging in water cooled to approximately
20C. Each SMP modified mesh retained a rolled shape once cooled, and was inserted
into the abdominal cavity of the swine using a 12mm laparoscopic cannula port. The
surgeon (Dr. Schoen) again positioned each mesh on the intestines and began
manipulation for placement. Similar to stage 1, all surgical meshes were secured using
5 mm tacks (Protack, Covidien).
4.3 Chronic Rat Studies
The investigate in vivo biocompatibility, a chronic rat study was completed. This
study was conducted under a test protocol approved by the Institutional Animal Care and
Use Committee (IACUC protocol 43812(08)1D) and the experiment was performed
using female Sprague Dawley rats weighing approximately 310-370g obtained from
Charles River Laboratories. Experimental procedure was based upon a procedure
outlined by Horan et al in 2009 [27], The porous SMP-mesh samples (Formula F) were


synthesized as previously described. Each rat was anesthetized before surgery using
ketamine and xylazine, or inhaled isoflurane. For pain relief, carprofen was administered
once a day subcutaneously the day of surgery, and for two days post-op.
Once anesthetized, each rat was placed in a supine position. Using surgical
dissection techniques, an opening in skin was created with a scalpel to expose the
abdominal muscle wall underneath. The scalpel was then used to create two small
punctures (0.5 cm x 1 cm or smaller) in the muscle wall to simulate a defect. The
punctures were positioned on each side of the animal abdominal wall, inferior to the
costal margin and superior to the pelvis. The implanted surgical meshes implanted
measured approximately 1 cm x 2 cm. The left side of the animal received the
experimental SMP-integrated porous mesh, and the right side of the animal received the
unmodified control mesh. Each surgical mesh was positioned subcutaneously over the
defect and secured to the muscle wall using non-absorbable sutures. The opening of skin
previously exposed was closed to cover the surgical mesh and abdominal wall using
sutures and surgical clips. An example of the puncture created is shown in Figure 9a, and
implantation of the surgical mesh is shown in Figure 9b.
27


Figure 9 (a) abdominal wall defect is created; (b) repaired with implanted surgical mesh
and the wound is closed with clips.
28


5 Experimental Results
Experimental results for Dynamic Mechanical Analysis, Uniaxial Tensile Testing,
Time-To-Unroll, Cytotoxicity, Acute Porcine Studies, and Chronic Rat Studies are
presented in this chapter.
5.1 Dynamic Mechanical Analysis
A sample of each SMP formula was characterized by storage modulus and the tan delta
curve. The glass transition temperature (Tg) was determined to be the peak of the tan
delta curve. Selected results are shown in Figure 10. A complete list of Tg results for all
polymer networks tested can be found in Appendix A, Table 7.
29


^ DMA Formula A (Tg= 57*C) 0 DMA Formula B (Tg= 37C)
Figure 10 Dynamic Mechanical Analysis (DMA) of formulas tested, (a) Formula A,
Tg=57C; (b) Formula B, Tg=37C; (c) Formula C, Tg=47C; (d) Formula D, Tg=44C.
The storage modulus of Formula A ranged from 1528.5 MPa to 3.6 MPa, Formula B
ranged from 1298.1 MPa to 4.1 MPa, Formula C ranged from 1176.7 MPa to 2.7 MPa,
and Formula D ranged from 970.7 MPa to 2.3 MPa. The glass transition temperature of
Formula A was found to be 57C, Formula B was found to be 37C, Formula C was
found to be 47C, and Formula D was found to be 44C. DMA analysis performed on
Formula F alone, Formula F + non-porous polyester mesh in the length and widthwise
directions are shown in Figure 11.
30
Tan-8 Tan-3


Figure 11 Formula F SMP/SMP-Mesh characteristics: a) SMP alone shows Tg = 41C;
b) SMP+Mesh tested in lengthwise direction shows Tg = 40C; c) SMP+Mesh tested in
widthwise direction shows Tg = 38. Indicates mesh has minimal effect on native SMP
Tg characteristics.
5.2 Uniaxial Tensile Tests
Uniaxial tensile tests were performed to characterize the tensile strength of SMP alone,
unmodified mesh alone, and SMP modified meshes. Tensile test results are shown in
Table 5, with sample size denoted n. A complete list of results for all formulations
tested is shown in Appendix A, Table 8.
31


Table 5 Selected Tensile Test Results
Tg (C) Tensile Strength (N) Strain to Failure (mm) n
Control PET mesh alone - 16.65 3.30 21.92 3.76 14
Formula A SMP alone 57 15.96 1.09 28.59 3.78 6
SMP + Mesh - 28.10 3.42 17.82 1.25 6
Formula B SMP alone 37 3.96 0.25 10.07 0.57 9
SMP + Mesh - 19.62 0.36 17.55 1.46 6
Formula C SMP alone 47 5.75 0.73 18.85 1.50 10
SMP + Mesh - 22.50 2.47 17.38 1.85 6
Formula D SMP alone 44 7.15 0.77 31.85 3.69 7
SMP + Mesh - 17.45 2.82 17.45 3.35 6
Formula F SMP alone 41 5.29 0.69 21.28 3.08 10
At high strain the SMP modified mesh behaved more like the control sample, in that
SMP began separating from the mesh and mesh fibers engaged similar to that of the
tensile test of the unmodified mesh. For this reason, SMP alone was tested to ensure
maximization of strain-to-failure. The strain-to-failure of SMP itself is shown in Figure
12.
32


40.00
35.00
E 30.00
E_
2 25.00
ro 20.00
LL
15.00
| 1000
5.00
0.00
Control
Mesh Only
Formula A
Tg = 57C
Formula B Formu,a c Formula D
Tg-37C jg = 47c Tg = 44C
Figure 12 Strain to Failure of SMP alone; Formula C and D show superior Tg and
strain-to-failure
It was observed that higher strain-to-failure reduced the separation observed between
SMP and mesh. Combining lower tensile strength and higher strain-to-failure in SMP
modified meshes suggests the SMP has less impact on the mechanical strength of the
mesh itself, allowing deformation to occur in a similar manner to that of unmodified
mesh. A Students T-test was used to compare strain-to-failure of the control (mesh
alone) and each SMP-modified mesh composite. No statistical difference between strain-
to-failure of the control and mesh modified with SMP was observed, as shown in Figure
13.
33


30.00
25.00
E
E 20.00
0)
'ro
15.00
o
+*
c
*(D
10.00
5.00
0.00
i
Formula A
Control (SMP+Mesh)
(Mesh Only) p=0.019
Formula B
(SMP+Mesh)
p=0.014
Formula C Formula D
(SMP+mesh) (SMP+Mesh)
p=0.012 p=0.022
Figure 13 No statistical difference is observed between the SMP modified mesh and the
control
5.3 Time to Unroll in Water
The time required for each formula to actively unroll the surgical mesh from the rolled
configuration to the fully deployed configuration is shown in Figure 14.
34


time --------------------------------
Tg(C) Time to Unroll (s)
Formula A 57C 113
Formula B 37C 3
Formula C 47C 23
Formula D 44C 7
Figure 14 Demonstration of unrolling (top panel) and time to unroll (bottom panel)
for each of the formulas, in 37C water bath. As Tg decreases, time to unroll also
decreases.
5.4 Cytotoxicity Study
The SMP-modified meshes presented a largely non-toxic response, receiving a score of
0 or 1 at 24, 48 and 72 hour incubation periods. Little to no reduction of cell growth
or cell lysis was seen. The SMP-modified meshes were deemed non-cytotoxic under the
test conditions employed. Results are presented in Table 6.
Table 6 Cytotoxicity Results
Polymer Network Score (24/48/72 h)
Formula F 0/0/0
Formula M 0/0/0
Formula P 0/1/1
35


5.5 Moisture Absorption
The percentage moisture absorbed by each sample was found to be less than 10% at
96 hours, a minimal change. The results are shown in Figure 15.
Figure 15 Moisture Absorption of Formula F
5.6 Acute Porcine Studies
Experiments were conducted under a test protocol approved by the Institutional
Animal Care and Use Committee (IACUC protocol 87909(05)ID).
5.6.1 Stage 1 Porcine Studies
This acute animal study was performed to evaluate the feasibility of an SMP-
modified mesh, automated unrolling and the effect of the added SMP on tacking and
suturing the mesh. Each SMP-modified mesh was inserted through a 12mm laparoscopic
port, positioned and tacked in place at the discretion of the surgeon (Schoen). While
monitoring intra-abdominal cavity temperature over the duration of the procedure, a
36


nominal temperature of 37.5C was noted. Each modified mesh was submerged in sterile
water held at 50C, which allowed the modified mesh to be rolled into a tight
configuration. The rolled mesh was then cooled by submerging in sterile water cooled to
less than 20C. In the rolled configuration, both Formula C and Formula D meshes were
easily inserted through the cannula port and manipulated using common laparoscopic
tools. Upon insertion into the abdominal cavity, the Formula C mesh did not unroll
automatically, and required considerable manipulation to achieve a flat configuration
prior to tacking to the abdominal wall, believed to be a result of the higher Tg. The total
time-to-unroll, with manual assistance, for Formula C mesh was 150 seconds. The
Formula D mesh however, did unroll automatically and required significantly less
manipulation, taking 33 seconds to completely unroll. In vivo unrolling of Formula C
mesh is shown in Figure 16 and unrolling of Formula D mesh is shown in Figure 17. A
yellow arrow identifies the thermocouple.
Figure 16 Significant laparoscopic manipulation was required to facilitate unrolling of
the Formula C PET-SMP surgical mesh within 150 seconds time (Tg = 47C).
37


Figure 17 Significantly less laparoscopic manipulation was required to unroll the
Formula D PET-SMP surgical mesh (Tg = 44C).
5.6.2 Stage 2 Porcine Studies
This acute animal study was performed to evaluate unrolling and placement of
modified and unmodified surgical mesh in an in vivo environment. Three surgical
meshes were evaluated: an unmodified polyester mesh, a non-porous Formula F SMP-
modified polyester mesh, and a porous Formula F SMP-modified polyester mesh. Each
surgical mesh was inserted through a 12mm laparoscopic port, positioned and tacked in
place. Mesh unrolling time was monitored over the duration of the procedure. Each
modified mesh was submerged in water held at 50C, which allowed the modified mesh
to be rolled into a tight configuration. The rolled mesh was then cooled by submerging in
water cooled to approximately 20C. In the rolled configuration, each mesh was easily
inserted through the cannula port and manipulated using common laparoscopic tools.
Upon insertion into the abdominal cavity, both SMP-modified meshes unrolled
38


automatically and required little manipulation. The unmodified mesh however, required
more manipulation to unroll and position. The fully coated SMP mesh unrolled with
minimal assistance in approximately 25 seconds and the porous SMP mesh unrolled in
approximately 31 seconds. In vivo unrolling of the non-porous SMP-modified mesh is
shown in Figure 18, and unrolling of the porous SMP-modified mesh is shown in Figure
19.
Figure 18 Non-Porous fully coated SMP-mesh automatically unrolls after 25 seconds as
the sample reaches body temperature.
39


Figure 19 Porous SMP-mesh automatically unrolls after 31 seconds as the sample
reaches body temperature
5.7 Chronic Rat Studies
Tissue ingrowth in hernia meshes is extremely important for repair strength,
therefore a chronic small animal study was performed to evaluate in vivo tissue ingrowth
of the porous SMP-modified surgical mesh. All four animals survived to the end of the
study, with no outward signs of infection or complications. An anterior view of a shaved
rat abdomen after 30 days post-op is shown in Figure 20. The SMP-modified mesh
sutures are identified by blue arrows and the control mesh sutures are identified by red
arrows. Contraction of each mesh was qualitatively observed. The SMP-modified mesh
showed markedly less contraction than the unmodified control mesh, as can be seen in
Figure 20. Mesh contraction is a normal process in wound healing, but may contribute to
hernia reoccurrence.
40


y ^ 30 days
post-op UL

Ctrl X i 1 Exp. Mesh
Mesh d Sutures
Sutures > r^.
k y / '
\ _£J
Figure 20 Abdominal view of a shaved rat 30 days post-op; red arrows (left) indicate
unmodified (control) mesh suture locations and blue arrows (right) indicate SMP-mesh
(experimental) suture locations.
Hematoxylin and eosin stained micrographs of the tissue reaction towards the unmodified
mesh are shown in Figure 21. Tissue reaction toward the SMP-modified mesh is shown
in Figure 22. Inflammatory response is similar, demonstrating expected tissue ingrowth
into mesh pores.
PET*
fibers
Figure 21 Unmodified control mesh tissue ingrowth. Inflammatory response is as
expected, demonstrating tissue ingrowth into polyester fibers and mesh pores.
41


Figure 22 SMP-modified mesh demonstrates similar tissue ingrowth characteristics.
Foreign body giant cells (FBGC), SMP, mesh fibers and fibrous encapsulation details are
identified in Figure 21 and Figure 22 with arrows. Neither gross examination before
tissue removal nor the micrographic histological images show evidence of acute
inflammation. Only a chronic inflammation response is seen, with foreign body giant cell
formation and fibrous encapsulation. If infection were present evidence would be first
seen upon gross examination, observing tissue swelling and purulent exudate.
Histological slides would show evidence of dead leukocytes and cellular debris. If the
tissue showed an adverse reaction to the biomaterial, gross examination would show a
sick and lethargic animal with abscesses and swelling at the implant site. Histological
slides could show evidence of acute inflammation, cytoplasmic vacuoles (frothy cell
appearance), granuloma, necrosis, and large numbers of multi-nucleated giant cells [28],
[29], Histological slides may also show evidence of tissue layer separation, dead cellular
debris, extracellular particles and a lack of fibrous encapsulation.
42


Picrosirius red staining was used to visualize collagen ingrowth into mesh. Picrosirius red
stained micrographs of tissue samples using the unmodified mesh are shown in Figure 23.
Micrographs of tissue samples using SMP-modified mesh are shown in Figure 24.
Figure 23 Picrosirius red stain displays collagen (red) integration into unmodified mesh
Figure 24 Picrosirius red stain displays collage (red) integration into SMP-modified
mesh.
43


6 Manufacturing Mold Development
The SMP-integrated surgical mesh described herein has notable clinical relevance.
In order to bring this device to a clinical marketplace, manufacturing of the mesh must
become standardized and capable of large production quantities. To facilitate
manufacturing, a mold fixture was developed for production of clinically relevant sizes of
SMP-integrated mesh.
6.1 Mold Design
In over 120 laparoscopic ventral hernia repairs, Perrone et al reported the average
hernia defect size was 10.9 cm2 and the average mesh size required for repair was 25.6
cm2 [30], Using these parameters as design criteria, a mold was designed with
dimensions approximately 22.5 cm x 25.4 cm. This design can accommodate mesh sizes
up to 19 cm x 19 cm, yielding a surface area up to 36.1 cm2. This size should be
sufficient for the majority of clinical cases. If necessary, scaling this mold design to a
larger fixture for larger mesh production is possible. An image of the mold is shown in
Figure 25.
44


Figure 25 Mold with Mesh Sample
The manufacturing mold consists of a series of clamps to compress two layers of
glass between two rectangular frames made of Delrin. The space created between the
layers of glass is sealed with a silicone gasket, and this makes up the polymerization
environment. The cross section of the mold is shown in Figure 26.
clamp
top
cushion layer
glass
\
cushion layer
Figure 26 Mold Cross-Section
45


A gas port and gas vent is inserted through the gasket to allow purging with an inert
gas, such as nitrogen (N2) or argon. These ports are on opposite ends of the fixture to
allow gas flow across the mesh. It is necessary to purge the mold environment with inert
gas to displace oxygen, as oxygen will inhibit polymerization by disrupting free-radical
propagation. A solution well is positioned on one side of the fixture to allow for excess
accumulation of polymer solution during the coating process. Solution is injected through
the gasket into this mesh polymerization area using a hypodermic needle in excess.
Polymer solution is propagates across the mesh with surface tension, and excess polymer
solution is directed to the solution well area. The polymer solution in the well is
polymerized with the mesh during the UV curing process, providing SMP test samples
for analysis. A graphic of this design is shown in Figure 27.
Delrin frame
mesh
polymerization
polymer
solution
gasket well
N2 gas
port
Figure 27 Manufacturing Mold with Polymer Solution Well
A uniform coating across the mesh is ensured by gently tilting or shaking the
fixture, either mechanically or by hand, until the solution has coated the mesh fibers by
46


surface tension but the mesh pores remain unencumbered. After the mesh is coated, the
mold assembly is tilted so that excess polymer solution accumulates in the well area.
After these steps are complete, the UV-polymerization process can begin as described in
Chapter 4.1. An example of an SMP-integrated mesh coated with this method was
previously shown in Figure 7. Several molds can be assembled in series with inert gas
sources for large scale production of multiple meshes.
6.2 UV-Polymerization
The polymerization process is accomplished by using a single or a dual UV source
setup. When using a single UV source, the source is positioned above the mold sample
the necessary distance to achieve the desired intensity at the sample for adequate curing
characteristics. A mirror is placed under the sample to allow UV light to reflect back onto
the sample. An example of this is shown in Figure 28.
47


UV source
UV Intensity
9-10
mW/cmA2
mirror
sample
117 mW/cmA2
21 mW/cmA2
18 mW/cmA2
\
benchtop
Figure 28 Single Source UV Polymerization Setup
In a dual UV source application, one source is positioned above and the other below
the mold sample at the necessary distances to achieve the desired intensity at each side of
the sample needed to complete the reaction. An example of this is shown in Figure 29.
48


UV source
UV source
Figure 29 Dual Source UV Polymerization Setup
6.3 Post-Polymerization Annealing
During the polymerization process, stresses may be induced into the newly created
co-polymer. These stresses result from the polymerization process being induced first on
the side facing the UV source. Annealing can be used to eliminate post-polymerization
stresses and make internal structures more homogeneous. A dual source setup can help
reduce the induced stress, but it may still be necessary to anneal the sample as one would
for a single source setup. The annealing process begins by opening the manufacturing
mold and heating the assembly to 80-85C for 2-3 hours to ensure conversion of all
monomers. The mesh sample is then removed from the mold and rinsed with warm tap


water to remove any dust particles or surface irregularities. The sample is then
sandwiched between two pieces of glass and heated to 70C for 24-72 hours, and then
allowed to cool at room temperature for 24-72 hours.
6.4 Sterilization
After the annealing process is complete, the newly created SMP-integrated meshes
are prepared for surgical implantation by steam sterilization. The mesh sample is exposed
to 121C for no more than 30 minutes and then allowed to dry for 15 minutes. This
method has been shown to be sufficient based on in vivo studies discussed in Chapter 5.7.
6.5 Sample Verification
The solution well described previously provides an area to polymerize test samples.
These test samples can be used to verify polymer solution characteristics as it is applied
to a specific lot of meshes. To demonstrate this capability, a sample of Formula F
independently manufactured from the described mold was characterized by storage
modulus and tan delta curve. The glass transition temperature (Tg) was determined to be
the peak of the tan delta curve. This data was compared to previously established data
made using previously described techniques (Chapter 5.1). DMA results are shown in
Figure 30.
50


Old Technique Formula F SMP (Tg = 41 C) | New Mold Formula F SMP (Tg = 42 C)
Figure 30 Formula F made using original technique compared to Formula F
manufactured with new mold
The glass transition temperature of Formula F was found to be 42C for the new mold,
which is comparable to the 41C glass transition temperature found with the original
technique. Storage modulus and tan delta curves closely match in both cases. This data
corresponds with previously established standards for Formula F as shown in Appendix
A, Table 7, indicating the described manufacturing mold has been successful in
producing SMP equal to previously established techniques.
51
Tan-8


7 Discussion
The placement of surgical mesh can be difficult in ventral hernia repair procedures.
The surgeon must roll or compact the mesh, force it through a cannula port into the
laparoscopic cavity, unfold the mesh, position it vertically to the repair site on the
abdominal wall, form the mesh to the anatomy and suture or tack it in place. This process
can require significant time during surgery, which can potentially increase the risk of
complications. To overcome the mesh placement difficulties, we propose integrating a
shape memory polymer into polyester surgical meshes to provide automated unrolling in
ventral hernia repair applications. Little biocompatibility data of SMPs has been
published in the literature; so, in continuation with our previous studies [25], we
evaluated a fully coated non-porous SMP-modified mesh, a porous SMP-modified
medium-weight polyester surgical meshes and unmodified polyester meshes in in vivo
studies.
When developing an SMP modified surgical mesh, two important considerations are
activation temperature and tissue ingrowth. Activation temperature (Tg) of the SMP
(Formula F) used in this work was found to be 41C. As shown in Figure 11, the
polyester surgical mesh has very little impact on the thermomechanical characteristics of
the pure SMP. Figure 18 illustrates the tested surgical mesh, fully encapsulated in SMP,
similar to a mesh previously described by our group [25], This mesh was non-porous and
thicker than typical surgical meshes used in ventral hernia repair applications and not
feasible for long term implantation. However, this mesh serves as a proof-of-concept and
experimental control to compare with the porous SMP-modified mesh and unmodified
52


mesh. The non-porous SMP-mesh took approximately 25 seconds to unroll and the
porous SMP-mesh took approximately 31 seconds to unroll. While the non-porous SMP-
mesh unrolled 9% faster than the porous SMP-mesh, the slight difference did not have a
noteworthy impact on mesh unrolling in vivo. This indicates the porous coating can be
applied in a minimalistic way, while achieving the desired unrolling effect and allowing
for tissue ingrowth.
In hernia repair applications, pore size of mesh is an important consideration for the
wound healing process. Fibroblasts, macrophages and other cells must infiltrate the mesh
pores to allow tissue reinforcing integration and prevent infection. To our knowledge, no
other research has been performed regarding biocompatibility of SMP integrated
composite surgical meshes. When creating a composite material which combines a new
SMP with an existing mesh, the biocompatibility and tissue ingrowth characteristics are
important considerations. As shown in Figure 21 and Figure 22, both experimental and
control meshes displayed similar characteristic fibrous encapsulation and presence of
foreign body giant cells, as expected with implantation. No notable differences with
chronic inflammatory response or tissue ingrowth were observed between the control and
experimental mesh implants.
The mechanism of tissue ingrowth into hernia meshes is thought to consist primarily
of collagen Type I and Type III, with the ratio between them having an effect on
reoccurrence of a hernia defect [31], How the mechanisms of collage ingrowth relate to
the unmodified and SMP-modified mesh is shown in Figure 31.
53


Cross-Section of unmodified mesh
Cross-Section of SMP-mesh
collagen ingrowth mesh
oo o0 o oo£oo ooo /oo o0o0p0oo0 OnOo00 o 0 ooOOo OOP O 0 ooo?,o OOoo 00
PET fibers SMP coating pore
size
Figure 31 Tissue ingrowth of: Unmodified mesh (top), with collagen fibers extending
between PET fibers and through mesh pores. SMP-modified mesh (bottom), with
collagen fibers extending through mesh pores only. SMP coating prevents thick scar
formation.
Tissue ingrowth is thought to occur in typical unmodified meshes by the creation of
a scar (collagen type I and III) encapsulating the mesh. Inflammatory cells and
fibroblasts migrate through mesh pores and between individual woven mesh strands,
laying down collagen to bind the mesh to surrounding tissue. In the SMP-modified mesh,
the SMP coating prevents ingrowth between individual mesh strands, but allows growth
through pores. By reducing the amount of cellular migration through individual mesh
fibers, scar formation appears thinner and less noticeable by touch. A thicker scar
54


formation suggests a patient may have more perceived foreign body sensation and
increased mesh contraction may be observed. Figure 23 and Figure 24 depict these
mechanisms, where red staining identifies collagen. In Figure 23, it can be observed that
individual woven mesh stands are separated and collagen fibers have been laid down as
fibroblasts migrate through the mesh. Conversely, in Figure 24, it can be observed that
collagen ingrowth has occurred between the pores, but not through individual mesh
strands. The SMP-modified mesh appears to create a thinner scar than the unmodified
mesh.
Mesh contraction was observed in both control and experimental groups; however,
the experimental group displayed markedly less contraction. This could potentially be
attributed to the SMP coating encapsulating the fine mesh fibers. The macroscopic pores
show similar tissue integration between the control and experimental groups, but in the
control group, individual mesh fibers begin to separate from the large weave as cells
infiltrate. In the experimental mesh, the SMP coats and penetrates the mesh fibers,
binding them together, and preventing cellular infiltration into individual fiber strands.
As was seen in the histologic slides, the SMP did not appear to hinder tissue ingrowth
between macroscopic pores however, and we hypothesize these factors may contribute to
a less severe inflammatory response, resulting in less perceptible scar formation, without
sacrificing reinforcing strength. It has been demonstrated that tissue contraction and
ingrowth characteristics change as implant size changes [32], [33]; therefore, larger
animal studies using a more clinically relevant mesh size would be a logical next step in
evaluating the SMP-modified mesh. These future studies should investigate conformity,
compliance, adhesion formation and ingrowth strength characteristics.
55


In order to bring this device to a clinical marketplace, manufacturing of the SMP-
integrated mesh must become standardized and capable of production in large quantities.
To facilitate manufacturing, a mold fixture was developed for production of clinically
relevant sizes up to 36.1 cm2. Samples of SMP-mesh were created with the mold fixture,
and these polymer samples had equal properties to those of samples made with
previously established methods. This fixture design can be scaled to larger sample sizes,
and provides a means for large scale batch production of SMP-integrated surgical mesh.
Arrays of molds could be connected to inert gas sources and polymerized using a dual
UV source setup. The multiple meshes polymerized could then be annealed in a large
oven, or series of ovens, and samples could subsequently be sterilized for clinical
packaging.
56


8 Future Directions
Future work will be centered on commercialization; developing this research-based
material into a commercially relevant medical device and product. According to a recent
report by Global Industry Analysts, Inc., the world market for hernia repair devices will
reach $1.5 billion by 2015 [34], Currently, surgical meshes are sold for approximately
$100 $1600 each; this technology will improve delivery functionality of these meshes,
which could command a 20 30% increase in price both due to the deployment
functionality but also the reduction in total surgical time. Further, given that there are a
small number of large, well-established players in this area, and that this technology
represents essentially a post-manufacturing step which does not require changes in the
original manufacturing process, it is possible attain acquisition interest in this technology.
This self-deploying surgical mesh would be an incremental improvement potentially
involving a 510(k) regulatory pathway. The FDA publishes a guidance document
specifically for hernia mesh devices, and using this document three categories of tests
have been identified to be included in any regulatory application: mechanical studies,
surgeon feedback studies, and a large animal survival study.
8.1 Mechanical Studies
Burst strength tests are a FDA requirement for 510(k) clearance of hernia meshes.
The ball-burst test should be performed using ASTM Test Method D3787-07, similar to a
test procedure outlined by Deeken et al. in 2011 [35], Consideration of mesh orientation
57


is not necessary because of the biaxial nature of this test. In this test, a one inch stainless
steel ball is applied in compression at 300 mm/min at room temperature in air and at body
temperature in water. A Students t-test can be used to evaluate any statistical difference
between the means of each group. The average bursting force the standard error of the
mean is documented. The ultimate tensile stress and strain at a stress of 16 N/cm is
documented for each sample. As outlined previously by Deeken et al., a ball-burst
strength of greater than 50 N/cm and a strain at 16N/cm of 10%-30% can be considered
acceptable [35],
Suture pull-out tests are a FDA requirement for 510(k) clearance of hernia meshes.
Suture pull-out strength tests should be performed using test methods similar to
procedures outlined by Deeken et al. in 2011 [35], This test measures the ability of the
mesh to retain sutures. A 0-polypropylene suture can be simulated by using a stainless
steel wire with a diameter of approximately 0.35mm. The stainless steel wire is passed
through the mesh specimen, and fixed to the base of the test frame. The mesh is pulled in
tension at a rate of 300 mm/minute until the stainless wire is pulled through the mesh.
The maximum load is recorded as the suture pull-out strength.
Tear resistance testing is a FDA requirement for 510(k) clearance of hernia meshes.
Tear resistance testing should be performed based on ASTM Test Method D2261-07a,
similar to a test procedure outlined by Deeken et al. in 2011 [35], This test measures the
force required to tear mesh fibers. Rectangular mesh specimens are partially cut along the
midline for half the length of the specimen, forming two tabs on a central backbone. One
tab is attached to the upper grip of the test frame, and the other tab is attached to the


lower grip of the test frame. The mesh is pulled in tension at a rate of 300 mm/minute
until the specimen is torn in half. The maximum load is recorded as the tear resistance
strength.
8.2 Direct Surgeon Feedback Studies
A Minimally Invasive Training System (3-DMed, Franklin, OH) should be used to
judge the effectiveness of manipulating and placing the modified meshes and unmodified
meshes. Twelve specimens should be evaluated, six modified meshes and six unmodified
meshes. Three examinees (volunteers surgeons and/or surgery fellows) that normally
perform minimally invasive hernia repair procedures would be required to complete
several tasks normally associated with laparoscopic procedures. Similar to a procedure
described by Derossis et al. in 1998 [36], the tasks should include positioning the mesh
specimen, cutting the specimen, positioning the specimen over a defect and suturing the
defect to a foam base material. The laparoscopic trainer environment should be heated to
approximately body temperature of 37C. Each examinee should be asked to perform the
cycle of tasks three times. The elapsed time for each cycle should be recorded, and the
surgeon should be asked to evaluate the level of difficulty of each task on a scale of 0-5,
with 0 being easy and 5 being very difficult. The average elapsed time and rating for each
task should be reported. The data should be analyzed using a linear regression method to
relate total performance scores and timing scores for each task.
59


8.3 Large Animal Studies
An in vivo survival porcine model should be used to evaluate automated unrolling,
placement and biocompatibility of the modified mesh in a human-like body size analog.
All porcine animal testing can be conducted at the University of Colorado Hospital
Animal Vivarium Operating Room. Each animal should undergo a surgical procedure to
compare two types of surgical meshes: one commercially available unmodified mesh as a
control, and one of the same type of mesh which has been modified with a novel shape
memory polymer. During the implantation surgery, both meshes can be secured using
transfascial sutures and tacking sutures as necessary. Surgical time should be monitored
as a metric to evaluate mesh placement efficiency, and intra-abdominal temperature
should be recorded if possible. This survival study should last 30 days, because based on
previous results from Majerik et. al. and Champault et. al., it has been shown that 30 days
is sufficient to evaluate tissue adhesion and surgical mesh effectiveness [37], [38], At the
completion of the study, the animals should be euthanized and each surgical mesh
previously implanted should be removed for evaluation. Histopathology studies should be
performed on excised mesh to investigate evidence of inflammation and foreign body
giant cells. A certain level of inflammation is required to recruit the cells necessary to
integrate surgical mesh into the abdominal wall. This animal model can serve as a proof-
of-concept evaluation of the surgical utility of the SMP-mesh concept, and provide a
building block toward a future FDA application.
60


9 Conclusion
Shape memory polymer integrated surgical meshes may provide a reduction in
surgical operating time. Shape memory polymers are synthesized by controlling
composition with two or more polymer components with specific cross-linking and glass
transition temperature characteristics. It is believed that integrating a shape memory
polymer could improve existing surgical mesh characteristics to facilitate automatic mesh
unrolling in vivo, without sacrificing the existing surgical mesh strength. Automated
mesh unrolling could greatly improve laparoscopic hernia repair outcomes and reduce
operating time. The SMP formulas developed for this application have shown excellent
preliminary in vivo biocompatibility in rats, and has shown excellent unrolling behavior
in vivo compared to unmodified mesh in an acute porcine model. It has also been
demonstrated that the SMP-integrated mesh can be produced reliably on a large scale
manufacturing platform. Next steps in the development of this SMP technology include
ball-burst mechanical studies, direct surgeon feedback studies and chronic large animal
studies using clinically relevant mesh sizes to evaluate longer term mesh contraction and
tissue ingrowth characteristics of SMP-modified meshes compared to unmodified
meshes.
61


BIBLIOGRAPHY
[A] The Surgical Clinic
< http://www.tsclinic.com/pg-laparoscopic-hernia-repair-tapp.html>
Image Retrieved 8/29/2013
[B] Davol, Inc
< http://www.davol.com/products/soft-tissue-reconstruction/hernia-repair/ventral-
hernia-repair/laparoscopic-repair-options/echo-ps/>
Image Retrieved 10/08/2013
[C] Covidien, Inc
< http://www.covidien.com/hernia/us/accumesh>
Image Retrieved 10/08/2013
62


REFERENCES
[1] C. M. Townsend, R. D. Beauchamp, B. M. Evers, and K. L. Mattox, Sabiston
Textbook of Surgery, 18th ed. .
[2] J. G. Hunter, Clinical trials and the development of laparoscopic surgery, Surg.
Endosc., vol. 15, pp. 1-3, Jan. 2001.
[3] J. A. Norton, P. S. Barie, R. R. Bollinger, A. E. Chang, S. F. Lowry, S. J. Mulvihill,
H. I. Pass, and R. W. Thompson, Eds., Surgery. New York, NY: Springer New
York, 2008.
[4] R. P. Tatum, S. Shalhub, B. K. Oelschlager, and C. A. Pellegrini, Complications of
PTFE Mesh at the Diaphragmatic Hiatus, J. Gastrointest. Surg., vol. 12, no. 5, pp.
953-957, Sep. 2007.
[5] W. W. Hope and D. A. Iannitti, An algorithm for managing patients who have
Composix Kugel ventral hernia mesh, Hernia, vol. 13, pp. 475-479, Apr. 2009.
[6] U.S. Food and Drug Administration (FDA): Center for Devices and Radiological
Health, Class 1 Recall: Bard Composix Kugel Mesh Patch Expansion, 22-
Dec-2005. [Online], Available:
http://www.fda.gov/MedicalDevices/Safety/RecallsCorrectionsRemovals/ListofRec
alls/ucm062944.htm. [Accessed: 05-Dec-2011],
[7] F. Berrevoet, C. Sommeling, S. Gendt, C. Breusegem, and B. Hemptinne, The
preperitoneal memory-ring patch for inguinal hernia: a prospective multicentric
feasibility study, Hernia, vol. 13, no. 3, pp. 243-249, Feb. 2009.
63


[8] C. Yakacki, R. Shandas, C. Lanning, B. Rech, A. Eckstein, and K. Gall,
Unconstrained recovery characterization of shape-memory polymer networks for
cardiovascular applications, BIOMATERIALS, vol. 28, no. 14, pp. 2255-2263, May
2007.
[9] A. Lendlein, M. Behl, B. Hiebl, and C. Wischke, Shape-memory polymers as a
technology platform for biomedical applications, EXPERT Rev. Med. DEVICES,
vol. 7, no. 3, pp. 357-379, May 2010.
[10] J. W. A. Burger, R. W. Luijendijk, W. C. J. Hop, J. A. Halm, E. G. G. Verdaasdonk,
and J. Jeekel, Long-term Follow-up of a Randomized Controlled Trial of Suture
Versus Mesh Repair of Incisional Hernia, Ann. Surg., vol. 240, no. 4, pp. 578-585,
Oct. 2004.
[11] E. J. DeMaria, J. M. Moss, and H. J. Sugerman, Laparoscopic intraperitoneal
polytetrafluoroethylene (PTFE) prosthetic patch repair of ventral hernia, Surg.
Endosc., vol. 14, no. 4, pp. 326-329, Apr. 2000.
[12] A. Park, M. Gagner, and A. Pomp, Laparoscopic repair of large incisional hernias,
Surg. Laparosc. Endosc., vol. 6, no. 2, pp. 123-128, Apr. 1996.
[13] B. L. Wake, K. McCormack, C. Fraser, L. Vale, J. Perez, and A. Grant,
Transabdominal pre-peritoneal (TAPP) vs totally extraperitoneal (TEP)
laparoscopic techniques for inguinal hernia repair., in Cochrane Database of
Systematic Reviews, The Cochrane Collaboration and K. McCormack, Eds.
Chichester, UK: John Wiley & Sons, Ltd, 2005.
64


[14] P. Prasad, O. Tantia, N. M. Patle, S. Khanna, and B. Sen, Laparoscopic
Transabdominal Preperitoneal Repair of Ventral Hernia: A Step Towards
Physiological Repair, Indian J. Surg., vol. 73, no. 6, pp. 403-408, Dec. 2011.
[15] J. Rives, J. C. Pire, J. B. Flament, J. P. Palot, and C. Body, Treatment of large
eventrations. New therapeutic indications apropos of 322 cases, Chir. Mem.
Academie Chir., vol. Ill, no. 3, pp. 215-225, 1985.
[16] R. E. Stoppa, The treatment of complicated groin and incisional hernias, World J.
Surg., vol. 13, no. 5, pp. 545-554, Sep. 1989.
[17] F. C. USHER, Hernia repair with knitted polypropylene mesh, Surg. Gynecol.
Obstet., vol. 117, pp. 239-240, Aug. 1963.
[18] I. L. Lichtenstein, A. G. Shulman, P. K. Amid, and M. M. Montllor, The tension-
free hernioplasty, Am. J. Surg., vol. 157, no. 2, pp. 188-193, Feb. 1989.
[19] Leber GE, Garb JL, Alexander AI, and Reed WP, Long-term complications
associated with prosthetic repair of incisional hernias, Arch. Surg., vol. 133, no. 4,
pp. 378-382, Apr. 1998.
[20] M. J. Rosen, Polyester-based mesh for ventral hernia repair: is it safe?, Am. J.
Surg., vol. 197, no. 3, pp. 353-359, Mar. 2009.
[21] A. Kingsnorth, M. Gingell-Littlejohn, S. Nienhuijs, S. Schiile, P. Appel, P. Ziprin,
A. Eklund, M. Miserez, and S. Smeds, Randomized controlled multicenter
international clinical trial of self-gripping Parietex ProGrip polyester mesh
versus lightweight polypropylene mesh in open inguinal hernia repair: interim
results at 3 months, Hernia, vol. 16, no. 3, pp. 287-294, Jun. 2012.
65


[22] C. Brown and J. Finch, Which mesh for hernia repair?, Ann. R. Coll. Surg. Engl.,
vol. 92, no. 4, pp. 272-278, May 2010.
[23] B. Lauren Paton, Y. W. Novitsky, M. Zerey, R. F. Sing, K. W. Kercher, and B.
Todd Heniford, Management of Infections of Polytetrafluoroethylene-Based
Mesh, Surg. Infect., vol. 8, no. 3, pp. 337-342, Jun. 2007.
[24] C. M. Yakacki, R. Shandas, D. Safranski, A. M. Ortega, K. Sassaman, and K. Gall,
Strong, tailored, biocompatible shape-memory polymer networks, Adv. Fund.
Mater., vol. 18, no. 16, pp. 2428-2435, Aug. 2008.
[25] M. M. Zimkowski, M. E. Rentschler, J. Schoen, B. A. Rech, N. Mandava, and R.
Shandas, Integrating a novel shape memory polymer into surgical meshes
decreases placement time in laparoscopic surgery: An in vitro and acute in vivo
study, J. Biomed. Mater. Res. A, pp. 2613-2620, 2013.
[26] C. M. Yakacki, R. Shandas, D. Safranski, A. M. Ortega, K. Sassaman, and K. Gall,
Strong, tailored, biocompatible shape-memory polymer networks, Adv. Fund.
Mater., vol. 18, no. 16, pp. 2428-2435, Aug. 2008.
[27] R. Horan, D. Bramono, J. Stanley, Q. Simmons, J. Chen, H. Boepple, and G.
Altman, Biological and biomechanical assessment of a long-term bioresorbable
silk-derived surgical mesh in an abdominal body wall defect model, HERNIA, vol.
13, no. 2, pp. 189-199, Apr. 2009.
[28] J. M. Anderson, Biological Responses to Materials, Annu. Rev. Mater. Res., vol.
31, no. 1, pp. 81-110, 2001.
66


[29] O. E. Dadzie, M. Mahalingam, M. Parada, T. El Helou, T. Philips, and J. Bhawan,
Adverse cutaneous reactions to soft tissue fillers a review of the histological
features, J. Cutan. Pathol., vol. 35, no. 6, pp. 536-548, 2008.
[30] J. M. Perrone, N. J. Soper, J. C. Eagon, M. E. Klingensmith, R. L. Aft, M. M.
Frisella, and L. M. Brunt, Perioperative outcomes and complications of
laparoscopic ventral hernia repair, Surgery, vol. 138, no. 4, pp. 708-716, Oct.
2005.
[31] A. Baktir, O. Dogru, M. Girgin, E. Aygen, B. H. Kanat, D. O. Dabak, and T.
Kuloglu, The effects of different prosthetic materials on the formation of collagen
types in incisional hernia, Hernia, vol. 17, no. 2, pp. 249-253, Apr. 2013.
[32] U. Klinge, J. Conze, B. Klosterhalfen, W. Limberg, B. Obolenski, A. P. Ottinger,
and V. Schumpelick, Changes in abdominal wall mechanics after mesh
implantation. Experimental changes in mesh stability, Langenbecks, vol. 381, no.
6, pp. 323-332, Nov. 1996.
[33] R. Gonzalez, K. Fugate, D. McClusky III, E. M. Ritter, A. Lederman, D. Dillehay,
C. D. Smith, and B. J. Ramshaw, Relationship Between Tissue Ingrowth and Mesh
Contraction, World J. Surg., vol. 29, no. 8, pp. 1038-1043, Aug. 2005.
[34] I. Global Industry Analysts, Hernia Repair Devices: A Global Market Report.
Jun-2010.
[35] C. Deeken, M. Abdo, M. Frisella, and B. Matthews, Physicomechanical Evaluation
of Polypropylene, Polyester, and Polytetrafluoroethylene Meshes for Inguinal
Hernia Repair, J. Am. Coll. Surg., vol. 212, no. 1, pp. 68-79, Jan. 2011.
67


[36] A. M. Derossis, G. M. Fried, M. Abrahamowicz, H. H. Sigman, J. S. Barkun, and J.
L. Meakins, Development of a Model for Training and Evaluation of Laparoscopic
Skills, Aw. J. Surg., vol. 175, no. 6, pp. 482-487, Jun. 1998.
[37] S. Majercik, V. Tsikitis, and D. A. Iannitti, Strength of tissue attachment to mesh
after ventral hernia repair with synthetic composite mesh in a porcine model, Surg.
Endosc. Interv. Tech., vol. 20, no. 11, pp. 1671-1674, Nov. 2006.
[38] G. Champault, C. Polliand, F. Dufour, M. Ziol, and L. Behr, A self adhering
prosthesis for hernia repair: experimental study, HERNIA, vol. 13, no. 1, pp. 49-
52, Feb. 2009.
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APPENDIX A: TABLES
Table 7 List of all polymer solutions prepared
Formulas Evaluated
Compositio n tBA nBA PEG DMA 550 PEG DMA 750 PEG DMA 1000 iBA EHA EBECR YL 8411 Tg (C) Strai n (mm)
Formula O 90% 10% 54 >45
Formula A 80% 20% 57 28.59
Formula B 65% 15% 20% 37 9.93
Formula C 75% 10% 15% 47 18.85
Formula D 80% 20% 44 31.85
Formula El 77% 23% 40 18.73
Formula E2 77% 23% 40 18.31
Formula F 78% 22% 41 21.28
Formula G 76% 4% 20% 38 20.05
Formula H 76% 4% 2% 18% 35 18.27
Formula J 75% 5% 1% 19% 36 20.01
Formula K 80% 15% 5% 47 37.62
Formula L 76% 19% 5% 42 23.60
Formula M 79% 19% 2% 40 26.98
Formula N 79% 19% 2% 43 26.43
Formula P 78% 15% 3.5% 3.5% 43 31.63
Table 8 Tensile results for all networks tested
Formulas Evaluated
SMP Tg (C) Tensile Strength (N) Strain to Failure (mm) n
Control mesh alone - 16.65 3.30 21.92 3.76 14
Formula SMP alone 57 15.96 1.09 28.59 3.78 6
A SMP + Mesh - 28.10 3.42 17.82 1.25 6
Formula SMP alone 37 3.96 0.25 9.93 0.64 9
B SMP + Mesh - 19.62 0.36 17.55 1.46 6
Formula SMP alone 47 5.75 0.73 18.85 1.50 10
C SMP + Mesh - 22.50 2.47 17.38 1.85 6
Formula SMP alone 44 7.15 0.77 31.85 3.69 7
D SMP + Mesh - 17.45 2.82 17.45 3.35 6
69


Formula El SMP alone 40 5.28 0.45 18.73 1.54 11
Formula E2 SMP alone 40 4.89 0.59 18.31 1.54 10
Formula F SMP alone 41 5.29 0.69 21.28 3.08 10
Formula G SMP alone 38 4.53 0.85 20.05 2.66 10
Formula H SMP alone 35 4.56 0.64 18.27 1.91 9
Formula J SMP alone 36 4.58 0.47 20.01 1.52 10
Formula K SMP alone 47 7.32 0.74 37.62 3.48 18
Formula L SMP alone 42 5.65 0.84 23.60 3.30 20
Formula M SMP alone 40 6.20 0.86 26.98 3.44 11
Formula N SMP alone 43 5.95 0.76 26.43 3.00 12
Formula O SMP alone 54 6.16 0.26 44.81 0.78 6
Formula P SMP alone 43 5.58 0.70 31.63 3.35 12
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Full Text

PAGE 1

INTEGRATING A NOVEL SHAPE MEMORY POLYMER INTO SURGICAL MESHES TO IMPROVE DEVICE PERFORMANCE DURING LAPAROSCOPIC HERNIA SURGERY by MICHAEL M. ZIMKOWSKI B.S., University of Toledo, 2005 M.S., University of Colorado Boulder, 2010 A thesis submitted to t he Faculty of the Graduate School of the University of Colorado Denver in partial fulfillment of the requirement for the degree of Doctor of Philosophy Bioengineering 2013

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ii This thesis for the Doctor of Philosophy degree by Michael M. Zimkowski has been approved for the Department of Bioengineering by Kendall H unter, Chair Robin Shandas, Advisor Daewon Park Mark E. Rentschler Jonathan Schoen November 14 2013

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iii Zimkowski, Mic hael M. (Ph.D., Bioengineering) Integrating a Novel Shape Memory Polymer into Surgical Meshes To Improve Device Performance During Laparoscopic Hernia Surgery Thesis dire cted by Professor Robin Shandas ABSTRACT About 600,000 hernia repair surgeries are performed each year. The use of laparoscopic minima lly invasive techniques has become increasingly popular in these operations. Use of surgical mesh in hernia repair has shown lower recurrence rates compared to other repair methods. However in many procedures, placement of surgical mesh can be challenging and even complicate the procedure, potentially leading to lengthy operating times. Various techniques have been attempted to improve mesh placement, including use of specialized systems to orient the mesh into a specific shape, with limited success and acc eptance. In this work, a programmed novel Shape Memory Polymer (SMP) was integrated into commercially available polyester surgical meshes to add automatic unrolling and tissue conforming functionalities, while preserving the intrinsic structural properties of the original surgical mesh. Tensile testing and Dynamic Mechanical Analysis was performed on four different SMP formulas to identify appropriate mechanical properties for surgical mesh integration. In vitro testing involved monitoring the time required for a modified surgical mesh to deploy in a 37C water bath. An acute porcine model was used to test the in vivo unrolling of SMP integrated surgical meshes. The SMP integrated surgical meshes produced an automated, temperature activated, controlled deplo yment of surgical mesh on the order of several seconds, via laparoscopy in the animal model. A 30 day chronic rat model was used to test initial in vivo subcutaneous biocompatibility. To produce large more clinical relevant sizes of mesh, a

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iv mold was develo ped to facilitate manufacturing of SMP integrated surgical mesh. The mold is capable of manufacturing mesh up to 361 cm 2 which is believed to accommodate the majority of clinical cases. Results indicate surgical mesh modified with SMP is capable of laparo scopic deployment in vivo activated by body temperature, and possesses the necessary strength and biocompatibility to function as suitable ventral hernia repair mesh, while offering a reduction in surgical operating time and improving mesh placement chara cteristics. Future work will include ball burst tests similar to ASTM D3787 07, direct surgeon feedback studies, and a 30 day chronic porcine model to evaluate the SMP surgical mesh in a realistic hernia repair environment, using laparoscopic techniques fo r typical ventral hernia repair. The form and content of this abstract are approved. I recommend its publication. Approved: Robin Shandas

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v ACKNOWLEDGEMENTS I would like to give special thanks to Professor Robin Shandas for his incredible directio n and guidance, Dr. Jonathan Schoen, Professor Kendall Hunter, Professor Mark Rentschler and Professor Daewon Park for serving on my committee. I would also like to thank Dr. Nageswara Mandava for initial concepts and input related to the medical device di scussed in this dissertation.

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vi CONTENTS Chapter 1 Introduction ................................ ................................ ................................ ....... 1 2 Background and Motivation ................................ ................................ ............... 4 2.1 Surgical Methods ................................ ................................ ....................... 5 2.1.1 Laparoscopic Intra Peritoneal Prosthetic Patch (LIPP) Approach ........ 6 2.1.2 Tr ans Abdominal Pre Peritoneal (TAPP) Laparoscopic Approach ...... 6 2.1.3 Totally Extra Peritoneal (TEP) Laparoscopic Approach ...................... 7 2.1.4 O pen Hernia Repair ................................ ................................ ............ 8 2.2 Conventional Repair Options ................................ ................................ ..... 9 2.2.1 Polypropylene Mesh ................................ ................................ ........... 9 2.2.2 Polyester (polyethylene terephthalate) Mesh ................................ ..... 10 2.2.3 Expanded polytetrafluoroethylene (ePTFE) ................................ ...... 10 2.3 Exis ting Mesh Placement Options ................................ ............................ 11 2.3.1 Traditional Mesh Placement Technique ................................ ............ 11 2.3.2 Bard Echo PS™ Positioning System ................................ ................. 12 2.3.3 Covidien AccuMesh Positioning System ................................ .......... 13 2.4 Proposed Shape Memory Polymer System ................................ ............... 14 3 Stage 1 Device Development: Synthesis and In Vitro Testing .......................... 15 3.1 Chemistry ................................ ................................ ................................ 15 3.2 Synthesis ................................ ................................ ................................ .. 18 3.3 Dynamic Mechanical Analysis ................................ ................................ 19

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vii 3.4 Uniaxial Tensile Tests ................................ ................................ .............. 19 3.5 Time to Unroll in Water ................................ ................................ ........... 20 3.6 Moisture Absorption ................................ ................................ ................ 21 3.7 Cytotoxicity Study ................................ ................................ ................... 22 4 In vivo Animal Testing ................................ ................................ ..................... 23 4.1 Synthesis ................................ ................................ ................................ .. 23 4.2 Acute Porcine Studies ................................ ................................ .............. 24 4.2.1 Stage 1 Porcine Studies ................................ ................................ .... 25 4.2.2 Stage 2 Porcine Studies ................................ ................................ .... 26 4.3 Chronic Rat Studies ................................ ................................ .................. 26 5 Experimental Results ................................ ................................ ....................... 29 5.1 Dynamic Mechanical Analysis ................................ ................................ 29 5.2 Uniaxial Tensile Tests ................................ ................................ .............. 31 5.3 Time to Unroll in Water ................................ ................................ ........... 34 5.4 Cytotoxicity Study ................................ ................................ ................... 35 5.5 Moisture Absorption ................................ ................................ ................ 36 5.6 Acute Porcine Studies ................................ ................................ .............. 36 5.6.1 Stage 1 Porcine Studies ................................ ................................ .... 36 5.6.2 Stage 2 Porcine Studies ................................ ................................ .... 38 5.7 Chronic Rat Studies ................................ ................................ .................. 40 6 Manufacturing Mold Development ................................ ................................ .. 44 6.1 Mold Design ................................ ................................ ............................ 44 6.2 UV Polymerization ................................ ................................ .................. 47

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viii 6.3 Post Polymerization Annealing ................................ ................................ 49 6.4 Sterilization ................................ ................................ .............................. 50 6.5 Sample Verification ................................ ................................ ................. 50 7 D iscussion ................................ ................................ ................................ ....... 52 8 Future Directions ................................ ................................ ............................. 57 8.1 Mechanical Studies ................................ ................................ .................. 57 8. 2 Direct Surgeon Feedback Studies ................................ ............................. 59 8.3 Large Animal Studies ................................ ................................ ............... 60 9 Conclusion ................................ ................................ ................................ ....... 61 B ibliography ................................ ................................ ................................ ............ 62 R eferences ................................ ................................ ................................ ............... 63 A ppendix A. Tables ................................ ................................ ................................ ................. 69

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ix LIST OF TABLES Table 1 Chemical Structure of Primary Components ................................ ............................. 16 2 SMP Polymerization Chemistry ................................ ................................ ................ 17 3 Polymer Networks Tested ................................ ................................ ......................... 18 4 – Polymer Networks for Cytotoxicity Testing ................................ .............................. 18 5 – Selected Tensile Test Results ................................ ................................ ................... 32 6 Cytotoxicity Results ................................ ................................ ................................ 35 7 – List of all polymer solutions prepared ................................ ................................ ...... 69 8 – Tensile results for all networks tested ................................ ................................ ....... 6 9

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x LIST OF FIGURES Figure 1 Trans Abdominal Pre Peritoneal (TAPP) Laparoscopic repair method [A] .................. 7 2 Total Extra Peritoneal (TEP) laparoscopic repair method [1] ................................ ...... 8 3 Bard Echo PS™ Positioning System, with inflation balloon (green) attached to mesh (wh ite) [B] ................................ ................................ ................................ ..................... 13 4 Covidien AccuMesh Positioning System [C] ................................ ............................ 14 5 – (a) Dynamic Mechanical Analysis diagram (b) Uniaxial Tensile Tes t diagram ......... 20 6 Time to unroll test procedure ................................ ................................ .................... 21 7 – (A) unmodified mesh; (B) SMP coated porous polyester surgical mesh .................... 24 8 Non porous SMP modified polyester surgical mesh ................................ .................. 24 9 (a) abdominal wall defect is created; (b) repaired with implanted surgica l mesh ....... 28 10 Dynamic Mechanical Analysis (DMA) of formulas tested, (a) Formula A, Tg=57C; (b) Formula B, Tg=37C; (c) Formula C, Tg=47C; (d) Formula D, Tg=44C. .............. 30 11 – Formula F SMP/SMP Mesh characteristics: a) SMP alone shows Tg = 41C; b) SMP+Mesh tested in lengthwise direction shows Tg = 40C; c) SMP+Mesh tested in widthwise direction shows Tg = 38. Indicates mesh has mini mal effect on native SMP Tg characteristics. ................................ ................................ ................................ .......... 31 12 Strain to Failure of SMP alone; Formula C and D show superior Tg and strain to failure ................................ ................................ ................................ ............................ 33 13 No statistical difference is observed between the SMP modified mesh and the control ................................ ................................ ................................ ................................ ...... 34

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xi 14 Demonstration of unrolling (top panel) and time to unroll (bottom panel) for eac h of the formulas, in 37C water bath. As Tg decreases, time to unroll also decreases. .......... 35 15 – Moisture Absorption of Formula F ................................ ................................ ......... 36 16 – Significant laparoscopic manipulation was required to facilitate unrolling of the C PET SMP surgical mesh within 150 seconds time (Tg = 47C). ................................ ..... 37 17 – Significantly less laparoscopic m anipulation was required to unroll the Formula D PET SMP surgical mesh (Tg = 44C). ................................ ................................ ........... 38 18 Non Porous fully coated SMP mesh automatically unrolls after 25 seconds as the sample reaches body t emperature. ................................ ................................ .................. 39 19 Porous SMP mesh automatically unrolls after 31 seconds as the sample reaches body temperature ................................ ................................ ................................ .................... 40 20 Abdomi nal view of a shaved rat 30 days post op; red arrows (left) indicate unmodified (control) mesh suture locations and blue arrows (right) indicate SMP mesh (experimental) suture locations. ................................ ................................ ..................... 41 21 Unmodified control mesh tissue ingrowth. Inflammatory response is as expected, demonstrating tissue ingrowth into polyester fibers and mesh pores. .............................. 41 22 – SMP modified mesh demonstrates sim ilar tissue ingrowth characteristics. ............. 42 23 Picrosirius red stain displays collagen (red) integration into unmodified mesh ........ 43 24 Picrosirius red stain displays collage (red) integration into SMP modified mesh. .... 43 25 – Mold with Mesh Sample ................................ ................................ ........................ 45 26 Mold Cross Section ................................ ................................ ................................ 45 27 Manufacturing Mold with Polymer Solution Well ................................ ................... 46 28 – Single Source UV Polymerization Setup ................................ ................................ 48

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xii 29 Dual Source UV Polymerization Setup ................................ ................................ ... 49 30 Formula F made using original technique compared to Formula F manufactured with new mold ................................ ................................ ................................ ....................... 51 31 Tissue ingrowth of: Unmodified mesh (top), with collagen fibers extending between PET fibers and through mesh pores. SMP modified mesh (bottom), with collagen fibers extending through mesh pores only. SMP coating prevents thick scar formation. ........... 54

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xiii LIST OF ABBREVIATION S DMA – Dynamic Mechanical Analysis ePTFE expanded polytetrafluorethylene FBGC – foreign body giant cell FDA – Food and Drug Administrati on IACUC – Institutional Animal Care and Use Committee PET – polyethylene terephthalate (commonly called polyester) SMP – Shape Memory Polymer TAPP – Trans Abdominal Pre Peritoneal TEP – Total Extra Peritoneal laparoscopic approach Tg – Glass Transition Te mperature (or “Activation Temperature”) UV – ultra violet

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1 1 Introduction Hernia repair surgery is one of the more common surgical procedures, with more than 600,000 hernia repair operations performed annually in the United States [1] Hernia repair often involves abdominal wall tissue reinforcement as it is widely accepted to reduce hern ia recurrence rates. Minimally invasive laparoscopic surgery has become increasingly popular in recent years and is often used to decrease surgical trauma and recovery time, including in hernia repair procedures [2] [1] S ynthetic meshes have become popular as a tissue reinforcement material in both open and laparoscopic procedures because these materials provide flexibility and strength. Newer meshes may also include absorbab le and composite types. Absorbable meshes are designed to break down over time, eventually being replaced with natural tissue. Composite types combine two materials, such as synthetic material and an absorbable material. Many laparotomies performed each ye ar involve incisional/ventral hernias, where reinforcing mesh can be challenging for the surgeon to position. Despite the challenges of mesh, surgical outcomes has confirmed that reduced morbidity and lower recurrence rates can be achieved by reinforcing the tissue with a surgical mesh [3] As mentioned, in many laparoscopic hernia repair procedures the placement of surgical mesh can present a challenge and even complicated the procedure [4] The surgical mesh must be rolled and folded into a cannula port, inserted into an abdominal port and released near the abdominal area to be repaired. Once in the a bdominal cavity, the surgical mesh must be unrolled, formed to fit the anatomy and attached with sutures

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2 or a variety of other means. Unrolling and tamping of the surgical mesh can require significant amounts of time, which may increase surgical complicati ons such as recurrence, infection or pain. Various techniques have been attempted to make mesh placement easier, including the introduction of a shape memory functionality. One of example of this has been the use of specialized geometry or manufacturing r einforcement rings to push mesh into a specific shape, all of which have had limited success [5] Perhaps the most well known example is the Davol Bard Composix Kugel patch, which was voluntarily recalled due to risk of breakage resulting in potent ially dangerous complications [6] This patch incorporated a stiff polymer which must be bent to accommodate the cannula port and then is rel eased into the abdominal cavity wherein elastic memory snapped the mesh into place. Reports of patient injury began to surface in 2002 and problems ultimately led to a series of FDA recalls from 2005 to 2007 [6] The cause of failure was eventually traced to a weld of the polyethylene terephthalate (PET – commonly called polyester) ring [6] The weld can break, causing the stiff wire to protrude from the repair site, resulting in fistula or other serious complications [6] Another example of a similar product is the Davol Bard Polysoft surgical mesh, which also utilizes a polyester/PET ring inside a polypropylene mesh [7] Products of this nature utilize elastic memory to “snap” the hernia me sh into position, an intrinsically dangerous process since the deployment is uncontrolled. A shape memory polymer (SMP) can be used to obtain controlled deployment. A SMP is a classification of polymers that provide tailorable mechanical functionalities, are

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3 capable of active movement into pre programmed shapes, and can be compressed into a small shape and later unfolded into a functional shape using a trigger, such as temperature [8] [9] SMPs have gained increased notice over the past several years as potential biomaterials for minimally invasive surgical devices [8] [9] They have already been used in orthopedic, cardiovascular and ophthalmic applications, showing good biocompatibility and tissue in growth [8] This work introduces a novel thermally activated SMP, which can be applied to commercially available surgical meshes using an ultra violet (UV) polymerization process.

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4 2 Background and Motivation A her nia is defined as a “protrusion or projection of an organ or part of an organ through the wall of the cavity that normally contains it” [3] Hernia repair often involves tissue reinforcement. The development of abd ominal wall reinforcements can be traced back to 1894, when Phelps introduced the concept of using a silver wire coil on the floor of the inguinal canal [3] In the more modern age, stainless steel was used to form w ire rings for use as reinforcements, but these systems were plagued with reports of fragmentation and erosion into abdominal structures [3] As polymers became more popular as biomaterials, their use as a reinforceme nt mesh became a natural step due to the increased flexibility compared to metal ring predecessors. Polymeric materials have included regenerated cellulose (Fortisan), polyvinyl alcohol (Ivalon), nylon, acrylic cloth (Orlon), fiberglass, polyester sheeti ng (Mylar), polytetrafluoroethylene (Teflon) and carbon fiber [3] When used in hernia repairs, many of these materials led to disintegration, rejection and required additional surgery for removal. The modern era o f hernia repair is often considered to have begun in 1958 when Francis Cowgill Usher published landmark experiences on fascia reinforcement and replacement biomaterials and worked with engineers to develop an optimal, novel hernia repair material – polypro pylene mesh, which showed great success in animals [3] From his work, the three main types of modern meshes were introduced: derivatives of polypropylene; polyester; and expanded polytetrafluorethylene (ePTFE) [3] Many newer types of meshes also combine absorbable, non absorbable and composite materials. Absorbable meshes are designed to break down over time, and are comprised of

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5 resorbable materials like polyglycolic acid (PG A) or collagen. Composite meshes also exist, such as combining ePTFE and polypropylene, or polyester and PGA. The later would be considered a partially absorbable composite mesh, using a synthetic material for strength and resorbable material to aid in tis sue integration. Examples of partially absorbable meshes include Ethicon UltraPro™ (polypropylene and PGA) and Covidien Parietex™ optimized composite mesh (polyester and collagen film). As previously noted, minimally invasive laparoscopic surgery has becom e increasingly popular in recent years and is often used to decrease surgical trauma and recovery time, including in hernia repair procedures [2] [1] In the United States, 4 to 5 million laparotomies are performed annually; approximately 20% of these involve incisional/ventral hernias (~400,000 to 500,000 / year) [10] Evaluating post laparoscopic surgery outcomes has confirmed that significantly reduced morbidity and lower recurrence rates can be achieved by reinforcin g the tissue with a surgical mesh [3] A 10 year follow up showed the cumulative rate of recurrence was 63% for suture only repair and 32% for repairs including mesh [10] In patients with small incisional hernias, the recurrence rate was 67% with a suture repair and 17% with a repair including mesh [10] Clearly, the use of mesh and laparoscopic techniques has made an important impact in reducing recurrence and surgical complications of hernia repair procedures. 2.1 Surgic al Methods Common surgical methods used to repair hernias included the Trans Abdominal Pre Peritoneal laparoscopic approach, the Total Extra Peritoneal laparoscopic approach, and

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6 the traditional open repair method. These methods are described in further de tail in the following sections. 2.1.1 Laparoscopic Intra Peritoneal Prosthetic Patch (LIPP) Approach T he Intra Peritoneal laparoscopic repair method is the primary procedure used for ventral hernia repair has been well documented [11], [12] This is the primary method referenced in this dissertation T he hernia repair is performed in a space created between the peritoneum and the intestines leaving the peritoneum attached to the abdominal wall An endoscope is inserted into the peritoneal cavity which is then insufflated to separate the peritoneum fr om the internal organs, creating a working space which is intraoperatively maintained with insufflation through laparoscopic ports. The hernia sac and any abdominal wall adhesions are dissected, and an appropriate sized mesh is chosen to overlap the hernia defect. The mesh is then tacked and sutured to the abdominal wall to cover the defect. Anteriorly the mesh is in contact with peritoneum and muscle wall and posteriorly the mesh is in contact with the intestines. As the inflammatory process proceeds durin g healing this direct contact between mesh and bowel can lead to adhesions, making mesh design an important consideration. 2.1.2 Trans Abdominal Pre Peritoneal (TAPP) Laparoscopic Approach In the Trans Abdominal Pre Peritoneal (TAPP) laparoscopic repair method the hernia repair is performed in a space created between the peritoneum and the intestines. An endoscope is inserted into the pre peritoneal space, which is then insufflated to separate the peritoneum from the internal organs, creating a working space w hich is

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7 intraoperatively maintained with insufflation through laparoscopic ports. Abdominal wall adhesions are divided and the hernia sac is reduced. T he peritoneum is dissected to reveal the defect, which is to be repaired with hernia mesh. Appropriate sized mesh is chosen to allow overlap with the defect, and it is fixed to the abdominal wall with tacks and sutures. Peritoneal flaps are then sutured back together, plac ing the peritoneum between the mesh and the intestines, which acts as barrier to preve nt adhesions. This is a common repair approach in inguinal hernia repair procedures [13] but recent studies have shown this as an option for ventral hernia procedures as well [14] An illustration of the TAPP approach is show n in Figure 1 Figure 1 Trans Abdominal Pre Peritoneal (TAPP) Laparoscopic repair method [A] 2.1.3 Totally Extra Peritoneal (TEP) Laparoscopic Approach The primary difference of the Total E xtra Peritoneal (TEP) laparoscopic repair method is that the hernia repair is performed in a space created between the muscle wall and the peritoneum. An endoscope with balloon is inserted into the peritoneal space, which is then inflated to separate the p eritoneum from the interior muscle wall, creating a

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8 pre peritoneal working space which is intraoperatively maintained with insufflation. The hernia sac is dissected and the defect is repaired with hernia mesh similar to the TAPP procedure This method do es not disturb the peritoneum and does not require entering the intra peritoneal space. This is a common repair approach in inguinal hernia repairs [13] An illustration the TEP approach is shown in Figure 2 Figure 2 Total Extra Peritoneal (TEP) laparoscopic repair method [1] 2.1.4 Open Hernia Repair Open hernia repair is performed by making an incision to dissect through the subcutaneous tissues and fascia. The external muscles and other local anatomy are

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9 identified and the dissection continues until the hernia sac is ident ified. The hernia sac is dissected away from any adjacent structures and examined for contents. Contents, such as intestine, are inserted back into the peritoneal space. A piece of synthetic mesh is cut to fit the defect, ensuring a 5 6 cm boarder overlap with tissue surrounding the defect. The mesh may be secured using sutures or tacks, or a combination of the two, however many surgeons rely on intra abdominal pressure alone to hold the mesh in place [1] [15] [16] 2.2 Conventional Repair Options Evaluations of post laparosco pic surgery outcomes has confirmed that significantly reduced morbidity and lower recurrence rates can be achieved by reinforcing the tissue with a surgical mesh [3] A 10 year follow up showed the cumulative rate of recurrence was 63% for suture only repair and 32% for repairs including mesh [10] In patients with small incisional hernias, the recurrence rate was 67% with a suture repair and 17% with a repair including mesh [10] Due to these results, suture only repairs have been largely abandoned. Clearly, the use of mesh and laparoscopic techniques has made an important impact in reducing recurrence and surgical complications of hernia repair procedures. 2.2.1 Polypropylene Mesh The use of polypropylene mesh was first introd uced by Usher in 1963 [17] It saw some success, but in 1989 Lichtenstein introduced the “tension free” repair, using polypropylene mesh, which showed excellent results [ 18] A“tension free” repair involves using mesh to strengthen the defect, without suturing the sides of the defect

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10 together, thereby eliminating tension in the adjacent muscles. This surgical approach has since become the preferred method of treatment, ma king polypropylene into one of the most common mesh materials in the United States of America. Examples of polypropylene mesh common in the hernia repair marketplace include Marlex™ (C.R. Bard/Davol, Inc), Prolene™ (Ethicon, Inc) and Parietene™ (Covidien L td). 2.2.2 Polyester (polyethylene terephthalate) Mesh The use of polyester mesh was introduced as a competitor to polypropylene. It has been used in similar indications as polypropylene mesh. Some data published during from the 1980s to 1990s suggested that p olyester had higher infection rates compared to polypropylene [19] However, more recently studies have shown polyester to be safe for hernia repairs [20] In fact, because polyester is a more pliable material with good strength, recent studies demonstrate that it may be more appropriate than polypropylene for hernia repairs [21] [22] As a result, polyester has become the preferred material in Europe and has surpassed polypropylene. Examples of polyester mesh common in the hernia repair marketplace include Mersilene™ (Ethicon, Inc) and Parietex™ (Covidi en Ltd). 2.2.3 Expanded polytetrafluoroethylene (ePTFE) The use of expanded polytetrafluorethylene (ePTFE) was introduced as a competitor to both polyester and polypropylene. It is also been used in similar indications as the other two materials. ePTFE meshes, like those offered by Gore Medical, have significantly smaller pore sizes, which prevent tissue adhesion, so they are often used in

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11 applications where bowel adhesion and the risk of fistula is of concern. Unfortunately, the small pores which prevent tissu e adhesion also prevent immune cells from fighting infections which may arise in ePTFE meshes [23] Examples of ePTFE mesh common in the hernia repair marketplace include Dulex™ (C.R. Bard/Davol, Inc), DualMesh™ (W. L. Gore & Associates), and Parietex™ Composite (Covidien Ltd). 2.3 Existing Mesh Placemen t Options Surgical mesh placement during ventral hernia repair continues to present a challenge to many surgeons. Traditional laparoscopic placement techniques involve marking the mesh, using orientation sutures and unfolding the mesh systematically in viv o Two systems are currently available to aid in mesh placement – the Bard Echo PS Positioning System, and the Covidien AccuMesh Positioning System. 2.3.1 Traditional Mesh Placement Technique Traditional laparoscopic ventral hernia repair starts with port inser tion. Typically, this repair involves the use of three ports, however additional ports may be inserted if necessary. Generally, a camera port is placed laterally in the upper left or right quadrant of the abdomen. Additional tool ports are generally placed in as far apart laterally as possible. The ventral hernia defect is identified, and the contents are dissected away from the hernia sac. Internally, the defect is measured using a sterile ruler, or externally the defect is measured by probing with a spina l needle. When measuring externally, a marker is used to draw the outline of the defect on the skin. Once the defect size has been determined, a mesh of the appropriate size is chosen to provide approximately 5 cm of

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12 overlap with healthy tissue. If necessa ry, the mesh is cut to fit. An orientation suture is placed in the center of the mesh, and additional lateral orientation sutures may also be attached to the mesh before insertion. A marker may also be used to identify anatomical orientation. The mesh is t hen rolled lengthwise and inserted through the largest laparoscopic port. After insertion into the abdominal cavity, the mesh is unrolled and manipulated into position so that the orientation sutures face anteriorly toward the defect. A suture passer is in serted through the abdominal wall from the outside, used to grasp the orientation sutures and raise the mesh into position over the defect. Alternatively, a mechanical fixation device utilizing tacks may be used to secure the mesh against the inside of the abdominal wall. Once fixed to the abdominal wall, the laparoscopic cavity can be deflated and the wounds can be closed. 2.3.2 Bard Echo PS™ Positioning System The steps of mesh placement are similar to the traditional technique, but modified for the use of the Bard Echo PS™ Positioning System. This system is designed for laparoscopic placement of their Ventralight™ ST or Composix™ L/P mesh. It utilizes a balloon scaffold system attached to the mesh, which is inflated in vivo for mesh placement, and later removed The mesh and balloon are pre packaged in tight roll inside an introducer tool. The introducer tool is centered over the defect site to facilitate mesh placement and defect repair, eliminating the need for orienting sutures. This device however requires e xtra steps to deflate the balloon and remove the balloon scaffold, making this a potentially cumbersome solution to mesh placement. The Bard Echo PS™ system is shown in Figure 3

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13 Figure 3 Bard Echo PS™ Positioning System, with inflation balloon (green) attached to mesh (white) [B] 2.3.3 Covidien AccuMesh Positioning System The Covidien AccuMesh™ Positioning System is designed for laparoscopic placement of the Covidien Parietex™ Optimized Comp osite Mesh. This positioning system uses a complicated mechanically expanding frame to facilitate mesh placement. The frame and mesh are inserted through a laparoscopic port in a compact form using a deployment tool. Inside the abdominal cavity, the frame is actuated using levers and sliders on the deployment tool to unroll the mesh and position it over the defect. The multitude of complex mechanical moving parts inherently makes this system prone to problems. The Covidien AccuMesh™ system is shown in Figure 4

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14 Figure 4 Covidien AccuMesh Positioning System [C] 2.4 Proposed Shape Memory Polymer System The aim of this work was to develop a SMP formula that could be integrated into surgical me sh and provide the capability of laparoscopic deployment, with unassisted in vivo unrolling. SMPs are defined by the ability to recover large deformations from a storage state in response to an environmental stimulus [8] which may be beneficial for a hernia mesh application Design criteria for the SMP to be integrated into surgical mesh required an ability to activa te upon exposure to body temperature with high strain to failure while imposing minimal change on the native mechanical strength of the mesh. Several SMP formulas were evaluated using the following tests: uniaxial tensile tests, dynamic mechanical analysis and measurement of time to unroll. Using these tests, SMP formulas were identified which showed useful glass transition temperature (Tg) and higher strain to failure. A SMP formula with a Tg around body temperature is most useful in this application. The se SMP formulas were then tested in vivo using a porcine model to evaluate efficacy of laparoscopic deployment and unassisted unrolling.

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15 3 Stage 1 Device Development: Synthesis and In Vitro Testing Creating the modified surgical mesh specimens was accompli shed by integrating the novel shape memory polymer (SMP) into a commercially available polyester mesh (PETKM14001 or PETKM7001, Textile Development Associates). Modified and unmodified surgical meshes were evaluated using dynamic mechanical analysis, tensi le strength, time to unroll and cytotoxicity tests 3.1 Chemistry Chemicals tert Butyl acrylate (tBA) poly(ethylene glycol) dimethacrylate (PEGDMA) 2,2 dimethoxy 2 phenylacetophenone (DMPA) photo initiator and other polymer components were combined to cre ate multiple polymer solutions Chemical structures of the three primary components are shown in Table 1 A complete list of polymer solutions is shown in Appendix A, Table 7

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16 Table 1 Chemical Structure of Primary Components Component Structure PEGDMA tBA DMPA (initiator) SMP creation proceeds by reacting networks of initiator, backbone and cross linkers together. T he reaction occurs by free radical polymerization initiated by ultra violet (UV) radiation. UV cleaves the bonds of the initiator DMPA homolytically, creating free radicals that attack vinyl groups (carbon carbon double bonds) of the backbone and cross lin ker. Backbone and cross linker connect together in a random network, and finally the reaction terminates as all radicals have been reacted. This reaction is demonstrated in Table 2

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17 Table 2 SMP Polymerization Chemistry Decomposition Initiation Termination

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18 3.2 Synthesis Polymer synthesis for each test was performed using a free radical UV polymerization process. Specific parameters are described below for each phase of synthesis. For initial DMA, Tensile and Time to Unroll testing, f our polymer solutions were selected for testing and prepared as shown in Table 3 A compl ete list of polymer networks tested is shown in Appendix A, Table 7 Table 3 Polymer Networks Tested tBA (wt%) nBA (wt%) PEGDMA (wt%) Formula A 80 0 20 (M n = 550) Formula B 65 15 20 (M n = 550) Formula C 75 10 15 (M n = 550) Formula D 80 0 20 (M n = 1000) For cytotoxicity testing, three polymer solutions were selected for testing and prepared as shown in Table 4 Table 4 – Polymer Networks for Cytotoxicity Testing tBA (wt%) iBA (wt%) EHA (wt%) PEGDMA (wt%) Formula F 78 0 0 2 2 (M n = 1000 ) Formula M 79 0 2 19 (M n = 1000 ) Formula P 79 2 0 19 (M n = 1000 ) P olymer solution was applied to commercially available surgical meshes using a free ra dical UV polymerization process. Similar combinations have been previously described by our group [8] [24] Surgical meshes were placed in glass molds (75 mm by 25 mm) in a flat configuration, and SMP solution was injected. The molds were then

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19 placed under a 365nm UV lamp (Model B100AP; Black Ray) for 10 minutes for photo curing. 3.3 Dynamic Mechanical Analysis Dynamic Mechanical Analysis (DMA) was performed in te nsile loading to determine glass transition temperature (Tg) and storage modulus of all SMP formulations. A graphical representation of the DMA test is shown in Figure 5 a. Using Formula F, a n additional DMA study w as performed using samples of SMP alone and with non porous SMP integrated mesh in both the lengthwise and widthwise directions to evaluate any potential change in Tg resulting from the SMP mesh composite formulation. A ll samples were cut to approximately 25 mm long x 5.5 mm wide x 1 mm thick and DMA was performed using a TA Q800 DMA The samples were thermally equilibrated at 0C for 5 minutes and then heated to 100C at a rate of 3C per minute. Testing was performed in cyclic strain control at 0.1% stra in and at a frequency of 1.0 Hz. A preload force of 0.01N and a force track setting of 125% were used. Tg was defined at the peak of the tan delta curve. 3.4 Uniaxial Tensile Tests SMP formulas alone, unmodified mesh materials and modified mesh materials with integrated SMP were tested. Uniaxial tensile tests were based upon ASTM Test Method D638 03, using Type V specimen geometry. This test procedure was similar to that outlined by Deeken et al. in 2011 [12]. Specimens measuring approximately 9.5 mm x 63.5 mm x 1 mm were cut using a D638 03 Type V cast steel die (North East Cutting Die

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20 Corp., Portsmouth, NH). A graphical representation of the uniaxial tensile test is shown in Figure 5 b. Figure 5 – (a) Dynamic Mechanical Analysis diagram (b) Uniaxial Tensile Test diagram Tensile tests were performed using an Insight 5SL test machine (MTS, Eden Prairie, MN), in an aqueous environmental chamber at 37C with the specimen immersed in deionized wate r, using a tension rate of 5 mm/min. 3.5 Time to Unroll in Water Developing a useful shape memory polymer for deploying a surgical mesh necessitates in vivo unrolling within a reasonable time, however the mesh should not unroll readily at typical operating ro om temperatures. The amount of time required for modified meshes to unroll was evaluated to determine the impact of adding shape memory polymer, as a function of temperature, similar to protocols previously described [9], [13], [14]. SMP modified mesh spec imens approximately 75 mm by 25 mm were

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21 p repared as previously described. E ach specimen was heated using hot water (>65C) to bring the sample into the rubbery region. The sample was rolled tightly by hand and cooled using cold water (< 7C) to bring the s ample into the glassy region to retain the rolled configuration. Using soft tipped forceps, each rolled mesh formula was individually deployed into a deionized water bath held at approximately 37C, to simulate introduction into a wet surgical environment The elapsed time for unassisted unrolling was recorded by video. A schematic of this process is shown in Figure 6 Figure 6 Time to unroll test procedure 3.6 Moisture Absorption Moisture absorption was measured using a submersion method at three different temperatures. A total of nine samples were submerged in 1X Phosphate Buffer Solution (PBS): three samples at room temperature, three samples at 37C, and three samples at 70C. These tem peratures test in the glassy region, body temperature and the rubbery

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22 region of the SMP. Each sample was weighed before submersion, and again at 24 hours, 48 hours, and 96 hours after submersion. The percentage of weight change is reported. 3.7 Cytotoxicity St udy Cytotoxicity testing was performed by WuXi AppTec, Inc (St. Paul, MN) using a MEM elution method compliant with ISO 10993 5:2009. Non porous SMP mesh es utilizing Formula F, M and P were used in this test to maximize sample exposure and sterilized by a utoclave. The test consists of an extraction process, an exposure process and experimental evaluation. The elution consists of placing 30 cm 2 of SMP mesh sample in 10 mL of Eagle’s MEM +5% fetal bovine serum. The sample was extracted at 37 C for 24 hours. The media was then inoculated into a L 929 mouse fibroblast cell line and the cells are incubated at 37 C. Cultures were evaluated for cytotoxic effects by microsc opic observation at 24, 48 and 72 hour incubation periods. Criteria for evaluating cytotox icity included morphologic changes in cells, such as granulation, crenation, or rounding, and loss of viable cells from the monolayer by lysis or detachment. Evaluation scoring was performed according to the ISO standards, wherein test results of ‘0’, ‘1’ or ‘2’ are considered non toxic and results of ‘3’ or ‘4’ are considered toxic.

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23 4 In vivo Animal Testing Unrolling behavior of modified surgical meshes was evaluated using in an acute porcine model and chronic biocompatibility was evaluated using a rat mod el Experiments were conducted under test protocols approved by the Institutional Animal Care and Use Committee (IACUC Protocol # 87912(04)1D and # 43812(08)1D). 4.1 Synthesis P olymer solution was applied to commercially available surgical meshes using UV po lymerization. Similar SMP combinations and shape memory polymer surgical meshes have been previously described by our group [25] [26] Surgical meshes were placed in glass molds (100 mm by 100 mm) in a flat configuration and SMP solution was injected and subsequently cured using a Dymax 2000 PC ultraviolet lamp Non porous SMP modified m eshes were created by filling the mold with SMP, resulting in a mesh embedded in SMP. Porous SMP modified meshes were created by first purging the mold with nitrogen gas, injecting enough SMP solution to coat the mesh fibers, and continually purging the mo ld with nitrogen gas during polymerization process to prevent oxygen inhibition. Excellent retention of the original pore size of the unmodified mesh was obtained using this process. A photomicrograph comparing an unmodified mesh with a porous SMP mesh is shown in Figure 7 A photomicrograph of a non porous SMP modified mesh is shown in Figure 8

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24 Figure 7 – (A) unmodified m esh; (B) SMP coated poro us polyester surgical mesh Figure 8 Non porous SMP modified polyester surgical mesh 4.2 Acute Porcine Studies This study was conducted under a test protocol approved by the Institutional Animal Care and Use Committee (IACUC protoc ol #87912(04)1D), and was performed in live female pigs weighing approximately 100 lbs. Each swine was anesthetized using ketamine and xylazine for induction and isoflurane for maintenance, and secured in a supine position. Several laparoscopic ports were inserted to perform experiments within

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25 the abdominal cavity. At the completion of testing, the animal was euthanized by anesthesia overdose. Formula C and D were chosen for the acute swine model test due to characteristics identified in tensile and DMA tes ting (Chapter 3). Surgical meshes were placed in glass molds (100 mm by 100 mm) in a flat configuration, and SMP solution was injected, and subsequently cured using UV energy to create non porous SMP integrated meshes After synthesis, modified and unmodif ied surgical mesh specimens were cut to approximately 70mm x 70mm to ensure uniform shape and size. Formula C specimen had a thickness of 0.68 mm, and Formula D specimen had a thickness of 1.0 mm. Final specimens were steam sterilized by a standard autocla ve system. 4.2.1 Stage 1 Porcine Studies The surgical procedure consisted of placing two SMP modified meshes (Formula C and D) against the porcine abdominal wall using standard intraperitoneal laparoscopic approach. Intra abdominal cavity temperature was monito red before insertion of each mesh using a thermometer (HH506RA, Omega). No peritoneal defect was created in this study. Modified surgical meshes were submerged in sterile water heated to 50C, rolled to fit into a cannula port and cooled by submerging in s terile water cooled to less than 20C. The SMP modified meshes retained the rolled shape, and were inserted into the abdominal cavity of the swine using a 12mm laparoscopic cannula port. The surgeon ( Dr. Schoen) positioned the modified mesh on the intestin es, and awaited automated unrolling as the temperature of the modified mesh increased to that of the abdominal cavity. Both meshes were then secured using 5mm tacks (Protack, Covidien) at four corners to evaluate feasibility of tack usage with added thickn ess of SMP. The thicker Formula D

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26 modified mesh was punctured twice using a suture grasper (Proxy Biomedical) to evaluate feasibility of penetration properties. 4.2.2 Stage 2 Porcine Studies In the second stage of porcine studies, the surgical procedure consis ted of placing three hernia meshes approximately 80 mm x 80 mm in size (fully SMP coated, porous SMP coated, and unmodified) were placed against the porcine abdominal wall using an intraperitoneal laparoscopic approach. No peritoneal defect was created in this study. Modified surgical meshes were submerged in water heated to approximately 5 0C, rolled to fit into a cannula port and cooled by submerging in water cooled to approximately 20C. Each SMP modified mesh retained a rolled shape once cooled, and was inserted into the abdominal cavity of the swine using a 12mm laparoscopic cannula port. The surgeon ( Dr. Schoen) again positioned each mesh on the intestines and began manipulation for placement. Similar to stage 1, a ll surgical meshes were secured using 5mm tacks (Protack, Covidien). 4.3 Chronic Rat Studies The investigate in vivo biocompatibility, a chronic rat study was completed. This study was conducted under a test protocol approved by the Institutional Animal Care and Use Committ ee (IACUC protocol 438 12(08)1D) and the experiment was performed using f emale Sprague Dawley rats weighing approximately 310 370g obtained from Charles River Laboratories Experimental procedure was based upon a procedure outlined by Horan et al in 2009 [27] The porous SMP mesh samples (Formula F) were

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27 synthesized as previously described Each rat was anesthetized before surgery using ketamine and xylazine, or inhaled isoflurane. For pain relief, carprofen was administered once a day subcutaneously the day of surgery, and for two days post op. Once anesthetized, each rat was placed in a supine posit ion. U sing surgical dissection techniques, an opening in skin was created with a scalpel to expose the abdominal muscle wall underneath. The scalpel was then used to create t wo small punct ures (0.5 cm x 1 cm or smaller) in the muscle wall to s imulate a defect The punctures were positioned on each side of the animal abdominal wall, inferior to the costal margin and superior to the pelvis. The implanted s urgical meshes implanted measured approximately 1 cm x 2 cm. The left side of the animal rec eived the experimental SMP integrated porous mesh, and the right side of the animal received the unmodified control mesh. Each surgical mesh was positioned subcutaneously over the defect and secured to the muscle wall using non absorbable sutures. The open ing of skin previously exposed was closed to cover the surgical mesh and abdominal wall using sutures and surgical clips An example of the puncture created is shown in Figure 9 a, and implantation of the surgical m esh is shown in Figure 9 b.

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28 Figure 9 (a) abdominal wall defect is created; (b) repaired with implanted surgical mesh and the wound is closed with clips.

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29 5 Experimental Results Experimen tal results for Dynamic Mechanical Analysis, Uniaxial Tensile Testing, Time To Unroll, Cytotoxicity, Acute Porcine Studies, and Chronic Rat Studies are presented in this chapter. 5.1 Dynamic Mechanical Analysis A sample of each SMP formula was characterized b y storage modulus and the tan delta curve. The glass transition temperature (T g ) was determined to be the peak of the tan delta curve. Selected r esults are shown in Figure 10 A complete list of Tg results for all polymer networks tested can be found in Appendix A, Table 7

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30 Figure 10 Dynamic Mechanical Analysis (DMA) of formulas tested, (a) Formula A, Tg=57C; (b) Formula B, Tg=37C; (c) Formul a C, Tg=47C; (d) Formula D, Tg=44C. The storage modulus of Formula A ranged from 1528.5 MPa to 3.6 MPa, Formula B ranged from 1298.1 MPa to 4.1 MPa, Formula C ranged from 1176.7 MPa to 2.7 MPa, and Formula D ranged from 970.7 MPa to 2.3 MPa. The glass transition temperature of Formula A was found to be 57C, Formula B was found to be 37C, Formula C was found to be 47C, and Formula D was found to be 44C. DMA analysis performed on Formula F alone Formula F + non porous polyester mesh in the length and widthwise directions are shown in Figure 11

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31 Figure 11 – Formula F SMP/SMP Mesh characteristics: a) SMP alone shows Tg = 41C; b) SMP+Mesh tested in lengthwise direction shows Tg = 40C; c) SMP+Mesh tested in widthwise direction shows Tg = 38. Indicates mesh has minimal effect on native SMP Tg characteristics. 5.2 Uniaxial Tensile Tests Uniaxial tensile tests were performed to characterize the tensile strength of SMP alone, unmodified mesh alone, and SMP modified meshes. Tensile test results are shown in Table 5 with sample size denoted “n”. A complete list of results for all formulations tested is shown in Appendix A, Table 8

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32 Table 5 – Selected Tensile Test Results Tg (C) Tensile Strength (N) Strain to Failure (mm) n Control PET mesh alone 16.65 3.30 21.92 3.76 14 Formula A SMP alone 57 15.96 1.09 28.59 3.78 6 S MP + Mesh 28.10 3.42 17.82 1.25 6 Formula B SMP alone 37 3.96 0.25 10.07 0.57 9 SMP + Mesh 19.62 0.36 17.55 1.46 6 Formula C SMP alone 47 5.75 0.73 18.85 1.50 10 SMP + Mesh 22.50 2.47 17.38 1.85 6 Formula D SMP alone 44 7.15 0.77 31.85 3.69 7 SMP + Mesh 17.45 2.82 17.45 3.35 6 Formula F SMP alone 41 5.29 0.69 21.28 3.08 10 At high strain the SMP modified mesh behaved more like the control sample, in that SMP began separating from the mesh and mesh fibe rs engaged similar to that of the tensile test of the unmodified mesh. For this reason, SMP alone was tested to ensure maximization of strain to failure. The strain to failure of SMP itself is shown in Figure 12

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33 Figure 12 Strain to Failure of SMP alone; Formula C and D show superior Tg and strain to failure It was observed that higher strain to failure reduced the separation observed between SMP and mesh. Combining lower tensile stren gth and higher strain to failure in SMP modified meshes suggests the SMP has less impact on the mechanical strength of the mesh itself, allowing deformation to occur in a similar manner to that of unmodified mesh. A StudentÂ’s T test was used to compare str ain to failure of the control (mesh alone) and each SMP modified mesh composite. No statistical difference between strain to failure of the control and mesh modified with SMP was observed, as shown in Figure 13

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34 Figure 13 No statistical difference is observed between the SMP modified mesh and the control 5.3 Time to Unroll in Water The time required for each formula to actively unroll the surgical mesh from the rolled configuration to th e fully deployed configuration is shown in Figure 14

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35 Figure 14 Demonstration of unrolling (top panel) and time to unroll (bottom panel) for each of the formulas, in 37C water bath. As Tg decreases, time to unroll also decreases. 5.4 Cytotoxicity Study The SMP modified mesh es presented a largely non toxic response, receiving a score of “0” or “1” at 24, 48 and 72 hour incubation periods. Little to n o reduction of cell growth or cell lysi s was se en. The SMP modified meshes were deemed non cytotoxic under the test conditions employed. Results are presented in Table 6 Table 6 Cytotoxicity Results Polymer Network Score (24/ 48/72 h) Formula F 0/0/0 Formula M 0/0/0 Formula P 0/1/1

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36 5.5 Moisture Absorption The percentage moisture absorbed by each sample was found to be less than 10% at 96 hours, a minimal change. The results are shown in Figure 15 Figure 15 – Moisture Absorption of Formula F 5.6 Acute Porcine Studies Experiments were conducted under a test protocol approved by the Institutional Animal Care and Use Committee (IACUC protocol 87909(05)1D). 5.6.1 Stage 1 P orcine Studies This acute animal study was performed to evaluate the feasibility of an SMP modified mesh, automated unrolling and the effect of the added SMP on tacking and suturing the mesh. Each SMP modified mesh was inserted through a 12mm laparoscopic port, positioned and tacked in place at the discretion of the surgeon (Schoen). While monitoring intra abdominal cavity temperature over the duration of the procedure, a

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37 nominal temperature of 37.5C was noted. Each modified mesh was submerged in sterile w ater held at 50C, which allowed the modified mesh to be rolled into a tight configuration. The rolled mesh was then cooled by submerging in sterile water cooled to less than 20C. In the rolled configuration, both Formula C and Formula D meshes were easil y inserted through the cannula port and manipulated using common laparoscopic tools Upon insertion into the abdominal cavity, the Formula C mesh did not unroll automatically, and required considerable manipulation to achieve a flat configuration prior to tacking to the abdominal wall, believed to be a result of the higher Tg. The total time to unroll, with manual assistance, for Formula C mesh was 150 seconds. The Formula D mesh ho wever did unroll automatically and required significantly less manipulation taking 33 seconds to completely unroll In vivo unrolling of Formula C mesh is shown in Figure 16 and unrolling of Formula D mesh is shown in Figure 17 A yellow arrow i dentifies the thermocouple. Figure 16 – Significant laparoscopic manipulation was required to facilitate unrolling of the Formula C PET SMP surgical mesh within 150 seconds time (Tg = 47C).

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38 Figure 17 – Significantly less laparoscopic manipulation was required to unroll the Formula D PET SMP surgical mesh (Tg = 44C). 5.6.2 Stage 2 Porcine Studies This acute animal study was performed to evaluate unrolling and placement of modified and unmodified surgical me sh in an in vivo environment. Three surgical meshes were evaluated: an unmodified polyester mesh, a non porous Formula F SMP modified polyester mesh, and a porous Formula F SMP modified polyester mesh. Each surgical mesh was inserted through a 12mm laparo scopic port, positioned and tacked in place. Mesh unrolling time was monitored over the duration of the procedure. Each modified mesh was submerged in water held at 50 C, which allowed the modified mesh to be rolled into a tight configuration. The rolled m esh was then cooled by submerging in water cooled to approximately 20C. In the rolled configuration, each mesh was easily inserted through the cannula port and manipulated using common laparoscopic tools. Upon insertion into the abdominal cavity, both SMP modified meshes unrolled

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39 automatically and required little manipulation. The unmodified mesh however, required more manipulation to unroll and position. The fully coated SMP mesh unrolled with minimal assistance in approximately 25 seconds and the porous SMP mesh unrol led in approximately 31 seconds In vivo unrolling of the non porous SMP modified mesh is shown in Figure 18 and unrolling of the porous SMP modified mesh is shown in Figure 19 Figure 18 Non Porous fully coated SMP m esh automatically unrolls after 25 seconds as the sample reaches body temperature.

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40 Figure 19 Porous SMP m esh automatically unrolls after 31 seconds as the sample reaches body temperature 5.7 Chronic Rat Studies Tissue ingrowth in hernia meshes is extremely important for repair strength, therefore a chronic small animal study was performed to evaluate in vivo tissue ingrowth of the porous SMP m odified surgical mesh. All four animals survived to the end of the study, with no outward signs of infection or complications. An anterior view of a shaved rat abdomen after 30 days post op is shown in Figure 20 T he SMP modified mesh sutures are identified by blue arrows and the control mesh sutures are identified by red arrows. Contraction of each mesh was qualitatively observed T he SMP modified mesh showed markedly less contraction than the unmodified control me sh as can be seen in Figure 20 Mesh contraction is a normal process in wound healing, but may contribute to hernia reoccurrence.

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41 Figure 20 Abdominal view of a shaved rat 30 days post op; red arrows (left) indicate unmodified (control) mesh suture locations and blue arrows (right) indicate SMP mesh (experimental) suture locations. Hematoxylin and eosin stained micrographs of the tissue reaction towards the unmodified mesh are shown in Figure 21 Tissue reaction toward the SMP modified mesh is shown in F igure 22 Inflammatory response is similar, demonstrating expected tissue ingrowth into mesh pores. Figure 21 Unmodified control mesh tissue ingrowth. Inflammatory response is as expected, demonstrating tissue ingrowth into polyester fibers and mesh pores.

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42 F igure 22 – SMP modified mesh demonstrates similar tissue ingrowth characteristics. Foreign body giant cells (FBGC), SMP, mesh fibers and fibrous encapsulation details are identified in Figure 21 and F igure 22 with arrows. Neither gross examination before tissue removal nor the micrographic histological images show evidence of acute inflammation. Only a chronic inflammation response is seen, with foreign body giant cell formation and fibrous encapsulation. If infect ion were present evidence would be first seen upon gross examination, observing tissue swelling and purulent exudate Histological slides would show evidence of dead leukocytes a nd cellular debris. If the tissue showed an adverse reaction to the biomateria l, gross examination would show a sick and lethargic animal with abscesses and swelling at the implant site Histological slides c ould show evidence of acute inflammation, cytoplasmic vacuoles (frothy cell appearance), granuloma, necrosis and large number s of multi nucleate d giant cells [28], [29] Histological slides may also show evidence of tissue layer separation dead cellular debris, extracellular particles and a lack of fibrous encapsulation

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43 Picrosirius red staining was used to visualize collagen ingrowth into mesh. Picrosirius red stained micrographs of tissue samples using the unmodified mesh are shown in Figure 23 Micrographs of tissue samples using SMP modified mesh are shown in Figure 24 Figure 23 Picrosirius r ed stain displays collagen (red) integration into unmodified mesh Figure 24 Picrosirius r ed stain displays collage (red) integration into SMP modified mesh.

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44 6 Manufacturing Mold Development The SMP integrated surgical mesh described herein has not able clinical relevance. In order to bring this device to a clinical marketplace, manufacturing of th e mesh must become standardi zed and capable of large production quantities. To facilitate manufacturing a mold fixture was developed for production of clinically relevant sizes of SMP integrated mesh. 6.1 Mold Design In over 120 laparoscopic ventral hernia repairs, Perrone et al reporte d the average hernia defect size was 10.9 cm 2 and the average mesh size required for repair was 25.6 cm 2 [30] Using these parameters as design criteria, a mold was designed with dimensions approximately 22.5 cm x 25.4 cm. This design can accommodate mesh sizes up to 19 cm x 19 cm, yielding a surface area up to 36.1 cm 2 This size should be sufficient for the majority of clinical cases. If necessary, scaling this mol d design to a larger fixture for larger mesh production is possible. An image of the mold is shown in Figure 25

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45 Figure 25 – Mold with Mesh Sample The manufacturing mold consists of a se ries of clamps to compress two layers of glass between two rectangular frame s made of Delrin The space created between the layers of glass is sealed with a silicone gasket, and this make s up the polymerization environment. The cross section of the mold i s shown in Figure 26 Figure 26 Mold Cross Section

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46 A gas port and gas vent is inserted through the gasket to allow purging with an inert gas, such as nitrogen (N2) or argon. These port s are on opposite ends of the fixture to allow gas flow across the mesh. It is necessary to purge the mold environment with inert gas to displace oxygen, as oxygen will inhibit polymerization by disrupting free radical propagation A solution well is posit ioned on one side of the fixture to allow for excess accumulation of polymer solution during the coating process Solution is injected through the gasket into this mesh polymerization area using a hypodermic needle in excess. Polymer solution is propagates across the mesh with surface tension, and excess polymer solution is directed to the solution well area. The polymer solution in the well is polymerized with the mesh during the UV curing process, p rovid ing SMP test samples for analysis. A graphic of this design is shown in Figure 27 Figure 27 Manufacturing Mold with Polymer Solution Well A uniform coating across the mesh is ensured by gently tilting or shaking the fixture either mech anically or by han d, until the solution has coated the mesh fibers by

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47 surface tension but the mesh pores remain unencumbered. After the mesh is coated, the mold assembly is tilted so that excess polymer solution accumulate s in the well area. After these s teps are complete, the UV polymerization process can begin as described in Chapter 4.1 An example of an SMP integrated mesh coated with this method was previously shown in Figure 7 Se veral molds can be assembled in series with inert gas sources for large scale production of multiple meshes. 6.2 UV Polymerization The polymerization process is accomplished by using a single or a dual UV source setup When using a single UV source, the sour ce is positioned above the mold sample the necessary distance to achieve the desired intensity at the sample for adequate curing characteristics A mirror is placed under the sample to allow UV light to reflect back onto the sample. An example of this is s hown in Figure 28

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48 Figure 28 – Single Source UV Polymerization Setup In a dual UV source application, one source is positioned above and the other below the mold sample a t the necessary distance s to achieve the desired intensity at each side of the sample needed to complete the reaction An example of this is shown in Figure 29

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49 Figure 29 Dua l Source UV Polymerization Setup 6.3 Post Polymerization Annealing Duri ng the polymerization process stresses may be induced into the newly created co polymer. These stresses result from the polymerization process being induced first on the side facing the UV source. Annealing can be u sed to eliminate post polymerization stresses and make internal structures more homogeneous. A dual source setup can help reduce the induced stress, but it may still be necessary to anneal the sample as one would for a single source setup. The annealing pr ocess begins by opening the manufacturing mold and heating the assembly to 80 85C for 2 3 hours to ensure conversion of all monomers. The mesh sample is then removed from the mold and rinsed with warm tap

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50 water to remove any dust particles or surface irre gularities The sample is then sandwiched between two pieces of glass and heated to 70C for 24 72 hours, and then allowed to cool at room temperature for 24 72 hours. 6.4 Sterilization After the annealing process is complete, the newly crea ted SMP integrated meshes are prepared for surgical implantation by steam sterilization. The mesh sample is exposed to 12 1C for no more than 30 minutes and then allowed to dry for 15 minutes. This method has been shown to be sufficient based on in vivo studies discussed in Chapter 5.7 6.5 Sample Verification The solution well described previously provides an area to polymerize test samples. These test samples can be used to verify polymer solution characteristics as it is applied to a specific lot of meshes. To demonstrate this capability, a sample of Formula F independently manufactured from the described mold was characte rized by storage modulus and tan delta curve. The glass transition temperature (Tg) was determined to be the pea k of the tan delta curve. This data was compared to previously established data made using previously described techniques (Chapter 5.1 ). DMA results are shown in Figure 30

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51 Figure 30 Formula F made using original technique compared to Formula F manufactured with new mold The glass transition temperature of Formula F was found to be 42C for the new mold, which is comparable to the 41C glass transition temp erature found with the original technique. Storage modulus and tan delta curves closely match in both cases. This data corresponds with previously established standards for Formula F as shown in Appendix A, Table 7 indicating the described manufacturing mold has been successful in producing SMP equal to previously established techniques

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52 7 Discussion The placement of surgical mesh can be difficult in ventral hernia repair procedures. The surgeon must roll or compac t the mesh, force it through a cannula port into the laparoscopic cavity, unfold the mesh, position i t vertically to the repair site on the abdominal wall, form the mesh to the anatomy and suture or tack it in place. This process can require significant ti me during surgery, which can potentially increase the risk of complications. To overcome the mesh placement difficulties, we propose integrating a shape memory polymer into polyester surgical meshes to provide automated unrolling in ventral hernia repair a pplications. Little biocompatibility data of SMPs has been published in the literature; so, in continuation with our previous studies [25] we evaluated a fully coated non porous SMP modified mesh, a porous SMP modified medium weight polyester surgical meshes and unmodified polyester meshes in in vivo studies. When developing an SMP modified surgical mesh, two important considerations are activation temperature and tissue ingrowth. Activation temperature (Tg) of the SMP (Formula F) used in this work was found to be 41C. A s shown in Figure 11 the polyester surgical mesh has very little impact on the thermomechanical characteri stics of the pure SMP. Figure 18 i llustrates the tested surgical mesh, fully encapsulated i n SMP, similar to a mesh previously described by our group [25] This mesh was non porous and thicker than typical surgical meshes used in ventral hernia repair applications and not feasible for long term implantation. However, this mesh serves as a proof of concept and experimental control to com pare with the porous SMP modified mesh and unmodified

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53 mesh. The non porous SMP mesh took approximately 25 seconds to unroll and the porous SMP mesh took approximately 31 seconds to unroll. While the non porous SMP mesh unrolled 9% faster than the porous SM P mesh, the slight difference did not have a noteworthy impact on mesh unrolling in vivo This indicates the porous coating can be applied in a minimalistic way, while achieving the desired unrolling effect and allowing for tissue ingrowth. In hernia repai r applications, pore size of mesh is an important consideration for the wound healing process. Fibroblasts, macrophages and other cells must infiltrate the mesh pores to allow tissue reinforcing integration and prevent infection. To our knowledge, no other research has been performed regarding biocompatibility of SMP integrated composite surgical meshes. When creating a composite material which combines a new SMP with an existing mesh, the biocompatibility and tissue ingrowth characteristics are important c onsiderations. As shown in Figure 21 and F igure 22 both experimental and control meshes displayed similar characteristic fibrous encapsulation and presence of foreign bod y giant cells, as expected with implantation. No notable differences with chronic inflammatory response or tissue ingrowth were observed between the control and experimental mesh implants. The mechanism of tissue ingrowth into hernia meshes is thought to consist primarily of collagen Type I and Type III, with the ratio between them having an effect on reoccurrence of a hernia defect [31] How the mechanisms of collage ingrowth relate to the unmodified and SMP modified mesh is shown in Figure 31

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54 Figure 31 T issue ingrowth of: U nmodified mesh (top), with c ollagen fibers extending between PET fibers and through mesh pores. SMP modified mesh (bottom), with collagen fibers ex tending through mesh pores only. SMP coating prevents thick scar formation. Tissue ingrowth is thought to occur in typical unmodified mes hes by the creation of a scar (collagen type I and III) encapsulating the mesh. Inflammatory cells and fibroblasts migrate through mesh pores and between individual woven mesh strands, laying down collagen to bind the mesh to surrounding tissue. In the S MP modified mesh, the SMP coating prevents ingrowth between individual mesh strands, but allows growth through pores. By reducing the amount of cellular migration through individual mesh fibers, scar formation appears thinner and less noticeable by touch. A thicker scar

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55 formation suggests a patient may have more perceived foreign body sensation and increased mesh contraction may be observed. Figure 23 and Figure 24 depict these mechanisms, where red staining identifies collagen. In Figure 23 it can be observed that individual woven mesh stands are separated and collagen fibers have been laid down as fibroblasts migrate through the mesh. Conversely, in Figure 24 it can be observed that collagen ingrowth has occurred between the pores, but not through individual mesh strands. The SMP modified mesh appears to create a thinner scar than the un modified mesh. Mesh contraction was observed in both control and experimental groups; however, the experimental group displayed markedly less contraction. This could potentially be attributed to the SMP coating encapsulating the fine mesh fibers. The mac roscopic pores show similar tissue integration between the control and experimental groups, but in the control group, individual mesh fibers begin to separate from the large weave as cells infiltrate. In the experimental mesh, the SMP coats and penetrates the mesh fibers, binding them together, and preventing cellular infiltration into individual fiber strands. As was seen in the histologic slides, t he SMP did not appear to hinder tissue ingrowth between macroscopic pores however, and we hypothesize these f actors may contribute to a less severe inflammatory response resulting in less perceptible scar formation, without sacrificing reinforcing strength. It has been demonstrated that tissue contraction and ingrowth characteristics change as implant size chang es [32], [33] ; therefore, larger animal studies using a more clinically relevant mesh size would be a logical next step in evaluating the SMP modified mesh. These future studies should investigate conformity, compliance, adhesion formation and ingrowth strength characteristics

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56 In order to bring this device to a clinical marketplace, manufacturing of the SMP integrated mesh must become standardized and capable of production in large quantities. To facilitate manufacturing, a mold fixture was developed for production of clinically relevant sizes up to 36.1 cm 2 S amples of SMP mesh wer e created with the mold fixture and these polymer samples had equal properties to those of samples made with previously established methods. This fixture design can be scaled to larger sample sizes, and provides a means for large sca le batch production of SMP integrated surgical mesh. Arrays of molds could be connected to inert gas sources and polymerized using a dual UV source setup. The multiple meshes polymerized could then be annealed in a large oven, or series of ovens, and sampl es could subsequently be sterilized for clinical packaging.

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57 8 Future Directions Future work will be centered on commercializ ation; developing this research based material into a commercially relevant medical device and product. According to a recent repo rt by Global Industry Analysts, Inc., the world market for hernia repair devices will reach $1.5 billion by 2015 [34] Currently, surgical meshes are sold for approximately $ 100 $1600 each; this technology will improve delivery functionality of these meshes, which could command a 20 – 30% increase in price both due to the deployment functionality but also the reduction in total surgical time. Further, given that there are a small number of large, well established players in this area, and that this technology represents essentially a post manufacturing step which does not require changes in the original manufacturing process, it is possible attain acquisition interest in thi s technology. This self deploying surgical mesh would be an incremental improvement potentially involving a 510(k) regulatory pathway. The FDA publishes a guidance document specifically for hernia mesh devices, and using this document three categories of t ests have been identified to be included in any regulatory application: mechanical studies, surgeon feedback studies, and a large animal survival study. 8.1 Mechanical Studies Burst strength tests are a FDA requirement for 510(k) clearance of hernia meshes. T he ball burst test should be performed using ASTM Test Method D3787 07, similar to a test procedure outlined by Deeken et al. in 2011 [35] Consideration of mesh orientation

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58 is not necessary because of the biaxial nature of this test. In this test, a one inch stainless steel ball is a pplied in compression at 300 mm/min at room temperature in air and at body temperature in water. A StudentÂ’s t test can be used to evaluate any statistical difference between the means of each group. The average bursting force the standard error of the m ean is documented. The ultimate tensile stress and strain at a stress of 16 N/cm is documented for each sample. As outlined prev iously by Deeken et al., a ball burst strength of greater than 50 N/cm and a strain at 16N/cm of 10% 30% can be considered accep table [35] Suture pull out t ests are a FDA requirement for 510(k) clearance of hernia meshes. Suture pull out strength tests should be performed using test methods similar to procedures outlined by Deeken et al. in 2011 [35] This test measures the ability of the mesh to retain sutures. A 0 polypropylene suture can be simulated by using a stainless steel wire with a diameter of approximately 0.35mm. The stainless steel wire is passed through the mesh specimen, and fixed to the base of the test frame. The mesh is pulled in tension at a rate of 300 mm/minute until the stainless wire is pulled through the mesh. The maximum load is recorded as the suture pull out strength. Tear resistance testing is a FDA requirement for 510(k) clearance of hernia meshes. Tear resistance testing should be performed based on ASTM Test Method D2261 07a, similar to a test procedure outlined by Deeken et al. in 2011 [35] This test measures the force required to tear mesh fibers. Rectangular mesh specimens are partially cut along the midline for half the length of the specimen, forming two tabs on a central backbone. One tab is attached to the upper grip of the test frame, and the other tab is attached to the

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59 lower grip of the test frame. The mesh is pulled in tension at a rate of 300 mm/minute until the specimen is torn in half. The maximum load is recorded as the tea r resistance strength. 8.2 Direct Surgeon Feedback Studies A Minimally Invasive Training System (3 DMed, Franklin, OH) should be used to judge the effectiveness of manipulating and placing the modified meshes and unmodified meshes. Twelve specimens should be e valuated, six modified meshes and six unmodified meshes. Three examinees (volunteers – surgeons and/or surgery fellows) that normally perform minimally invasive hernia repair procedures would be required to complete several tasks normally associated with l aparoscopic procedures. Similar to a procedure described by Derossis et al. in 1998 [36] the tasks should include positioning the mesh specimen, cutting the specimen, positioning the specimen over a defect and suturing the defect to a foam base materi al. The laparoscopic trainer environment should be heated to approximately body temperature of 37C. Each examinee should be asked to perform the cycle of tasks three times. The elapsed time for each cycle should be recorded, and the surgeon should be aske d to evaluate the level of difficulty of each task on a scale of 0 5, with 0 being easy and 5 being very difficult. The average elapsed time and rating for each task should be reported. The data should be analyzed using a linear regression method to relate total performance scores and timing scores for each task.

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60 8.3 Large Animal Studies An in vivo survival porcine model should be used to evaluate automated unrolling, placement and biocompatibility of the modified mesh in a human like body size analog. All porc ine animal testing can be conducted at the University of Colorado Hospital Animal Vivarium Operating Room. Each animal should undergo a surgical procedure to compare two types of surgical meshes: one commercially available unmodified mesh as a control, a nd one of the same type of mesh which has been modified with a novel shape memory polymer. During the implantation surgery, both meshes can be secured using transfascial sutures and tacking sutures as necessary. Surgical time should be monitored as a metric to evaluate mesh placement efficiency, and intra abdominal temperature should be recorded if possible. This survival study should last 30 days, because based on previous results from Majerik et. al. and Champault et. al., it has been shown that 30 days is sufficient to evaluate tissue adhesion and surgical mesh effectiveness [37] [38] At the completion of the study, the animals should be euthanized and each surgical mesh previously implanted should be removed for evaluation. Histopathology studies should be performed on excised mesh to investigate evidence of inflammation and foreign bo dy giant cells. A certain level of inflammation is required to recruit the cells necessary to integrate surgical mesh into the abdominal wall. This animal model can serve as a proof of concept evaluation of the surgical utility of the SMP mesh concept, and provide a building block toward a future FDA application.

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61 9 Conclusion Shape memory polymer integrated surgical meshes may provide a reduction in surgical operating time. Shape memory polymers are synthesized by controlling composition with two or more po lymer components with specific cross linking and glass transition temperature characteristics. It is believe d that integrating a shape memory polymer could improve existing surgical mesh characteristics to facilitate automatic mesh unrolling in vivo, witho ut sacrificing the existing surgical mesh strength. Automated mesh unrolling could greatly improve laparoscopic hernia repair outcomes and reduce operating time. The SMP formulas de veloped for this application have shown excellent preliminary in vivo bioco mpatibility in rats, and has shown excellent unrolling behavior in vivo compared to unmodified mesh in an acute porcine model. It has also been demonstrated that the SMP integrated mesh can be produced reliably on a large scale manufacturing platform. Next steps in the development of this SMP technology include ball burst mechanical studies, direct surgeon feedback studies and chronic large animal studies using clinically relevant mesh sizes to evaluate longer term mesh contraction and tissue ingrowth chara ct eristics of SMP modified meshes compared to unmodified meshes.

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62 BIBLIOGRAPHY [A] The Surgical Clinic < http://www.tsclinic.com/pg laparoscopic hernia repair tapp.html> Image Retrieved 8/29/2013 [B] Davol, Inc < http://www.davol.com/products/soft tissue reconstruction/hernia repair/ventral hernia repair/laparoscopic repair options/echo ps/> Image Retrieved 10/08/2013 [C] Covidien, Inc < http://www.covidien.com/hernia/us/accumesh> Image Retrieved 10/08/2013

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63 REFERENCES [1] C. M. Townsend, R. D. Beauchamp, B. M. Evers, and K. L. Mattox, Sabiston Textbook of Surgery 18th ed. [2] J. G. Hunter, “Clinical trials and the development of laparoscopic surgery,” Surg. Endosc. vol. 15, pp. 1 – 3, Jan. 2001. [ 3] J. A. Norton, P. S. Barie, R. R. Bollinger, A. E. Chang, S. F. Lowry, S. J. Mulvihill, H. I. Pass, and R. W. Thompson, Eds., Surgery New York, NY: Springer New York, 2008. [4] R. P. Tatum, S. Shalhub, B. K. Oelschlager, and C. A. Pellegrini, “Complicat ions of PTFE Mesh at the Diaphragmatic Hiatus,” J. Gastrointest. Surg. vol. 12, no. 5, pp. 953 – 957, Sep. 2007. [5] W. W. Hope and D. A. Iannitti, “An algorithm for managing patients who have Composix Kugel ventral hernia mesh,” Hernia vol. 13, pp. 475 – 479, Apr. 2009. [6] U.S. Food and Drug Administration (FDA): Center for Devices and Radiological Health, “Class 1 Recall: Bard Composix Kugel Mesh Patch Expansion,” 22 Dec 2005. [Online]. Available: http://www.fda.gov/MedicalDevices/Safety/RecallsCorr ectionsRemovals/ListofRec alls/ucm062944.htm. [Accessed: 05 Dec 2011]. [7] F. Berrevoet, C. Sommeling, S. Gendt, C. Breusegem, and B. Hemptinne, “The preperitoneal memory ring patch for inguinal hernia: a prospective multicentric feasibility study,” Hernia vol. 13, no. 3, pp. 243 – 249, Feb. 2009.

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64 [8] C. Yakacki, R. Shandas, C. Lanning, B. Rech, A. Eckstein, and K. Gall, “Unconstrained recovery characterization of shape memory polymer networks for cardiovascular applications,” BIOMATERIALS vol. 28, no. 14, p p. 2255 – 2263, May 2007. [9] A. Lendlein, M. Behl, B. Hiebl, and C. Wischke, “Shape memory polymers as a technology platform for biomedical applications,” EXPERT Rev. Med. DEVICES vol. 7, no. 3, pp. 357 – 379, May 2010. [10] J. W. A. Burger, R. W. Luijendijk W. C. J. Hop, J. A. Halm, E. G. G. Verdaasdonk, and J. Jeekel, “Long term Follow up of a Randomized Controlled Trial of Suture Versus Mesh Repair of Incisional Hernia,” Ann. Surg. vol. 240, no. 4, pp. 578 – 585, Oct. 2004. [11] E. J. DeMaria, J. M. Moss, and H. J. Sugerman, “Laparoscopic intraperitoneal polytetrafluoroethylene (PTFE) prosthetic patch repair of ventral hernia,” Surg. Endosc. vol. 14, no. 4, pp. 326 – 329, Apr. 2000. [12] A. Park, M. Gagner, and A. Pomp, “Laparoscopic repair of large incision al hernias,” Surg. Laparosc. Endosc. vol. 6, no. 2, pp. 123 – 128, Apr. 1996. [13] B. L. Wake, K. McCormack, C. Fraser, L. Vale, J. Perez, and A. Grant, “Transabdominal pre peritoneal (TAPP) vs totally extraperitoneal (TEP) laparoscopic techniques for ingui nal hernia repair.,” in Cochrane Database of Systematic Reviews The Cochrane Collaboration and K. McCormack, Eds. Chichester, UK: John Wiley & Sons, Ltd, 2005.

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65 [14] P. Prasad, O. Tantia, N. M. Patle, S. Khanna, and B. Sen, “Laparoscopic Transabdominal Pre peritoneal Repair of Ventral Hernia: A Step Towards Physiological Repair,” Indian J. Surg. vol. 73, no. 6, pp. 403 – 408, Dec. 2011. [15] J. Rives, J. C. Pire, J. B. Flament, J. P. Palot, and C. Body, “Treatment of large eventrations. New therapeutic indica tions apropos of 322 cases,” Chir. Mm. Acadmie Chir. vol. 111, no. 3, pp. 215 – 225, 1985. [16] R. E. Stoppa, “The treatment of complicated groin and incisional hernias,” World J. Surg. vol. 13, no. 5, pp. 545 – 554, Sep. 1989. [17] F. C. USHER, “Hernia re pair with knitted polypropylene mesh,” Surg. Gynecol. Obstet. vol. 117, pp. 239 – 240, Aug. 1963. [18] I. L. Lichtenstein, A. G. Shulman, P. K. Amid, and M. M. Montllor, “The tension free hernioplasty,” Am. J. Surg. vol. 157, no. 2, pp. 188 – 193, Feb. 1989. [19] Leber GE, Garb JL, Alexander AI, and Reed WP, “Long term complications associated with prosthetic repair of incisional hernias,” Arch. Surg. vol. 133, no. 4, pp. 378 – 382, Apr. 1998. [20] M. J. Rosen, “Polyester based mesh for ventral hernia repair: is it safe?,” Am. J. Surg. vol. 197, no. 3, pp. 353 – 359, Mar. 2009. [21] A. Kingsnorth, M. Gingell Littlejohn, S. Nienhuijs, S. Schle, P. Appel, P. Ziprin, A. Eklund, M. Miserez, and S. Smeds, “Randomized controlled multicenter international clinical tri al of self gripping Parietex TM ProGrip TM polyester mesh versus lightweight polypropylene mesh in open inguinal hernia repair: interim results at 3 months,” Hernia vol. 16, no. 3, pp. 287 – 294, Jun. 2012.

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66 [22] C. Brown and J. Finch, “Which mesh for hernia r epair?,” Ann. R. Coll. Surg. Engl. vol. 92, no. 4, pp. 272 – 278, May 2010. [23] B. Lauren Paton, Y. W. Novitsky, M. Zerey, R. F. Sing, K. W. Kercher, and B. Todd Heniford, “Management of Infections of Polytetrafluoroethylene Based Mesh,” Surg. Infect. vol 8, no. 3, pp. 337 – 342, Jun. 2007. [24] C. M. Yakacki, R. Shandas, D. Safranski, A. M. Ortega, K. Sassaman, and K. Gall, “Strong, tailored, biocompatible shape memory polymer networks,” Adv. Funct. Mater. vol. 18, no. 16, pp. 2428 – 2435, Aug. 2008. [25] M M. Zimkowski, M. E. Rentschler, J. Schoen, B. A. Rech, N. Mandava, and R. Shandas, “Integrating a novel shape memory polymer into surgical meshes decreases placement time in laparoscopic surgery: An in vitro and acute in vivo study,” J. Biomed. Mater. Re s. A pp. 2613 – 2620, 2013. [26] C. M. Yakacki, R. Shandas, D. Safranski, A. M. Ortega, K. Sassaman, and K. Gall, “Strong, tailored, biocompatible shape memory polymer networks,” Adv. Funct. Mater. vol. 18, no. 16, pp. 2428 – 2435, Aug. 2008. [27] R. Horan, D. Bramono, J. Stanley, Q. Simmons, J. Chen, H. Boepple, and G. Altman, “Biological and biomechanical assessment of a long term bioresorbable silk derived surgical mesh in an abdominal body wall defect model,” HERNIA vol. 13, no. 2, pp. 189 – 199, Apr. 2009 [28] J. M. Anderson, “Biological Responses to Materials,” Annu. Rev. Mater. Res. vol. 31, no. 1, pp. 81 – 110, 2001.

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67 [29] O. E. Dadzie, M. Mahalingam, M. Parada, T. El Helou, T. Philips, and J. Bhawan, “Adverse cutaneous reactions to soft tissue fillers – a review of the histological features,” J. Cutan. Pathol. vol. 35, no. 6, pp. 536 – 548, 2008. [30] J. M. Perrone, N. J. Soper, J. C. Eagon, M. E. Klingensmith, R. L. Aft, M. M. Frisella, and L. M. Brunt, “Perioperative outcomes and complications of laparo scopic ventral hernia repair,” Surgery vol. 138, no. 4, pp. 708 – 716, Oct. 2005. [31] A. Baktir, O. Dogru, M. Girgin, E. Aygen, B. H. Kanat, D. O. Dabak, and T. Kuloglu, “The effects of different prosthetic materials on the formation of collagen types in i ncisional hernia,” Hernia vol. 17, no. 2, pp. 249 – 253, Apr. 2013. [32] U. Klinge, J. Conze, B. Klosterhalfen, W. Limberg, B. Obolenski, A. P. Ottinger, and V. Schumpelick, “Changes in abdominal wall mechanics after mesh implantation. Experimental changes in mesh stability,” Langenbecks vol. 381, no. 6, pp. 323 – 332, Nov. 1996. [33] R. Gonzalez, K. Fugate, D. McClusky III, E. M. Ritter, A. Lederman, D. Dillehay, C. D. Smith, and B. J. Ramshaw, “Relationship Between Tissue Ingrowth and Mesh Contraction,” Wor ld J. Surg. vol. 29, no. 8, pp. 1038 – 1043, Aug. 2005. [34] I. Global Industry Analysts, “Hernia Repair Devices: A Global Market Report.” Jun 2010. [35] C. Deeken, M. Abdo, M. Frisella, and B. Matthews, “Physicomechanical Evaluation of Polypropylene, Polye ster, and Polytetrafluoroethylene Meshes for Inguinal Hernia Repair,” J. Am. Coll. Surg. vol. 212, no. 1, pp. 68 – 79, Jan. 2011.

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68 [36] A. M. Derossis, G. M. Fried, M. Abrahamowicz, H. H. Sigman, J. S. Barkun, and J. L. Meakins, “Development of a Model for T raining and Evaluation of Laparoscopic Skills,” Am. J. Surg. vol. 175, no. 6, pp. 482 – 487, Jun. 1998. [37] S. Majercik, V. Tsikitis, and D. A. Iannitti, “Strength of tissue attachment to mesh after ventral hernia repair with synthetic composite mesh in a porcine model,” Surg. Endosc. Interv. Tech. vol. 20, no. 11, pp. 1671 – 1674, Nov. 2006. [38] G. Champault, C. Polliand, F. Dufour, M. Ziol, and L. Behr, “A ‘self adhering’ prosthesis for hernia repair: experimental study,” HERNIA vol. 13, no. 1, pp. 49 – 52 Feb. 2009.

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69 APPENDIX A: TABLES Table 7 – List of all polymer solutions prepared Formulas Evaluated Compositio n tBA nBA PEG DMA 550 PEG DMA 750 PEG DMA 1000 iBA EHA EBECR YL 8411 Tg (C) Strai n (mm) Formula O 90% 10% 54 > 45 Formula A 80% 20% 57 28.59 Formula B 65% 15% 20% 37 9.93 Formula C 75% 10% 15% 47 18.85 Formula D 80% 20% 44 31.85 Formula E1 77% 23% 40 18.73 Formula E2 77% 23% 40 18.31 Formula F 78% 22% 41 21.28 Formula G 76% 4% 20% 38 20.05 Formula H 76% 4% 2% 18% 35 18.27 Formula J 75% 5% 1% 19% 36 20.01 Formula K 80% 15% 5% 47 37.62 Formula L 76% 19% 5% 42 23.60 Formula M 79% 19% 2% 40 26.98 Formula N 79% 19% 2% 43 26.43 Formula P 78% 15% 3.5% 3.5% 43 31.63 Table 8 – Tensile results for all networks tested Formulas Evaluated SMP Tg (C) Tensile Strength (N) Strai n to Failure (mm) n Control mesh a lone 16.65 3.30 21.92 3.76 14 Formula A SMP alone 57 15.96 1.09 28.59 3.78 6 SMP + Mesh 28.10 3.42 17.82 1.25 6 Formula B SMP alone 37 3.96 0.25 9.93 0.64 9 SMP + Mesh 19.62 0.36 17.55 1. 46 6 Formula C SMP alone 47 5.75 0.73 18.85 1.50 10 SMP + Mesh 22.50 2.47 17.38 1.85 6 Formula D SMP alone 44 7.15 0.77 31.85 3.69 7 SMP + Mesh 17.45 2.82 17.45 3.35 6

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70 Formula E1 SMP alone 40 5.28 0.45 18.73 1.54 11 Formula E2 SMP alone 40 4.89 0.59 18.31 1.54 10 Formula F SMP alone 41 5.29 0.69 21.28 3.08 10 Formula G SMP alone 38 4.53 0.85 20.05 2.66 10 Formula H SMP alone 35 4.56 0.64 18.27 1.91 9 Formula J SMP alone 36 4.58 0.47 20.01 1.52 10 Formula K SMP alone 47 7.32 0.74 37.62 3.48 18 Formula L SMP alone 42 5.65 0.84 23.60 3.30 20 Formula M SMP alone 40 6.20 0.86 26.98 3.44 11 Formula N SMP alone 43 5.95 0.76 26.43 3.00 12 Formula O SMP alone 54 6.16 0.26 44.8 1 0.78 6 Formula P SMP alone 43 5.58 0.70 31.63 3.35 12