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Prototyping and finite element analysis of tissue specific barbed sutures

ProQuest Dissertations and Theses, 2009
Dissertation
Author: Nilesh P Ingle
Abstract:
The project titled 'Prototyping and Finite Element Analysis of Tissue Specific Barbed Sutures' is focussed on understanding the relationship between barb geometry and mechanical behavior of barbed sutures. In this study size '0' polypropylene monofilament sutures of diameter 0.4mm were used for creating barbs at 150°, 160° and 170° cut angles and 0.07, 0.12 and 0.18mm cut depths. A new prototyping method was developed to create barbed sutures with precisely controlled geometries whichd used tMTS tensile testing machine to control cut depth. The cut samples were then characterized by image analysis to assess the reproducibility and the variability associated with the barbs geometric dimensions. Tensile testing and stress and bulk relaxation experiments were performed to obtain viscoelastic constants for finite element modeling. An experiment was run to quantify the peeling properties of a barb under point-pressure load by attaching a metal wire to the end of the barb. Suture/tissue pullout experiments were also performed using bovine tendon and porcine skin tissues. The finite element simulation of the point-pressure loading of a barb tip in ANSYS was validated by experimental results of the same materials by a margin of only 4%. Three sets of FEA simulations were then performed for each of the nine blocks of combination of barb geometries. The same three levels of cut angle and three levels of cut depth were selected. In addition point-pressure loading simulations were run and experimental suture/tissue pullout tests were performed on tendon and skin tissues. The experimental results revealed that since tendon tissue has a higher modulus than skin it needs a more rigid barb to penetrate and anchor into the surrounding tissue. A cut angle of 150° and 0.18mm cut depth are recommended. On the other hand for the softer skin tissue a cut angle of 170 degrees and 0.18 mm cut depth provided a more flexible barb that gives superior skin tissue anchoring. The simulations helped identify the areas of stress concentration. The cut line at the base of the cut appears to be the weakest part of the barb. So the geometry or design should be modified so that the stresses generated are lower. A new design with a circular cut line has been virtually prototyped and tested in ANSYS. This new and improved design helps to redistribute the stresses along the barb and its cut line so that peeling is initiated at higher stresses and improved anchoring performance.

vii TABLE OF CONTENTS LIST OF TABLES....................................................x LIST OF FIGURES...................................................xii 1 Introduction.......................................................1 1.1 Background..................................1 1.2 Objectives...................................2 1.3 Outline of Thesis...............................3 1.4 Abbreviations.................................4 2 Review of Literature...............................................5 2.1 Brief History.................................5 2.2 Suture Biomaterials.............................8 2.3 Classification of Sutures...........................13 2.4 Comparison of Knotted and Knotless Sutures...............14 2.5 Types of Knotless Sutures..........................14 2.6 Methods of Creating a Barb on a Monofilament Suture..........18 2.7 Suturing Techniques.............................23 2.8 Image Analysis of Barbed Sutures.....................26 2.9 Mechanical Properties............................28 2.9.1 Tensile.................................28 2.9.2 Suture/Tissue Pullout Test.....................31 2.9.3 Stress Relaxation...........................32 2.9.4 Cyclic Loading............................34 2.9.5 Surface Friction............................35 2.10 Chemical Stability..............................36 2.11 Antibacterial Sutures.............................38 2.12 Surgical Situations..............................38 2.12.1 Orthopedic..............................39 2.12.2 Dermal (Skin)............................43 2.12.3 Cardiovascular............................45 2.12.4 Gynecology..............................49 2.12.5 Pancreatic Fistula Surgery.....................50 2.12.6 Dermal Closures...........................51 2.12.7 Scalp Closure Wound........................51 2.12.8 Bone..................................51 2.12.9 Opthalmology.............................52 2.13 Structures of Tissues.............................54 2.13.1 Cardiovascular Tissues........................55 2.13.2 Respiratory and Digestive Tissues.................62 2.13.3 Urogenital Organ Tissues......................71 2.14 Biomechanics.................................73

viii 2.14.1 Symbols................................73 2.14.2 Vector Mathematics.........................75 2.14.3 Continuum Mechanics........................77 2.14.4 Constitutive Modeling........................80 2.14.5 Finite Element Modeling......................93 3 Barbed Suture Prototyping.........................................100 3.1 Principle....................................100 3.1.1 Methods to Mount Cutting Blade..................100 3.1.2 Batch Processes (Single and Multiple Barbs)...........100 3.2 Current Invention...............................101 3.2.1 Machine................................101 3.2.2 Continuous Process.........................101 3.2.3 Path of Suture............................101 3.2.4 Take-up Assembly..........................104 3.2.5 Let-off Assembly...........................105 3.2.6 Barb Suture Cutting Process Control...............105 3.2.7 Doffing................................106 3.2.8 Specimen Individualization.....................107 3.2.9 Horizontal Force Stabilizer (HFS)..................108 3.2.10 Zero Blade Calibration........................110 3.2.11 Cutting Zone (CZ)..........................115 3.2.12 Blade Assembly............................118 3.2.13 Cutting Base Assembly.......................122 3.2.14 Image Analysis System.......................124 3.2.15 Barb Quality.............................129 4 Materials and Methods.............................................132 4.1 Suture Material................................132 4.2 Image Analysis................................132 4.2.1 Barb geometry............................132 4.3 Design of Experiments............................133 4.4 Specimen Preparation............................134 4.4.1 Tensile test..............................134 4.4.2 Tissue Pullout Test.........................134 4.5 Experiments..................................137 4.5.1 Tensile Testing............................137 4.5.2 Single Barb Pressure Point Loading................138 4.5.3 Suture/Tissue Pullout Test.....................141 4.6 Finite Element Analysis...........................143 4.6.1 High Performance Computing Resources..............143 4.6.2 Suture material properties......................144 4.6.3 Tissue Material Properties......................152 4.6.4 Solid Modeling and Meshing....................154 4.6.5 New Design:’Geomcirc’......................166 4.6.6 Boundary conditions.........................168 4.7 Statistics...................................169

ix 4.7.1 Student T-test with Unequal Variance...............169 4.7.2 Analysis of Variance (ANOVA)...................169 5 Results and Discussion.............................................170 5.1 Images of Prototyped Barbed Sutures...................170 5.2 Image Analysis of Prototyped Barbed Sutures...............171 5.2.1 Diameter...............................171 5.2.2 Barb Geometry............................172 5.3 Tensile Testing................................174 5.3.1 Elongation at Peak Tensile Load..................174 5.3.2 Peak Tensile Load..........................177 5.4 Suture/Tissue Pullout Testing........................179 5.4.1 Skin Tissue..............................179 5.4.2 Tendon Tissue............................181 5.5 Finite Element Analysis...........................183 5.5.1 Point Loading of a Single Barb...................183 5.5.2 Effect of Varying the Cut Angle and Cut Depth.........185 5.5.3 New Design ’Geomcirc’.......................191 5.5.4 Tendon and Skin Tissue Pullout Test Simulations.........197 5.5.5 Limitations of FEA.........................210 5.5.6 Benefits of the FEA study......................211 6 Conclusions........................................................213 6.1 Prototyping..................................215 6.2 Experiments and Simulations........................215 7 Future Work.......................................................218 Appendices............................................................233 Appendix A..................................234 Appendix B..................................236 Appendix C..................................267 Appendix D..................................268 Appendix E..................................269 Appendix F..................................270 Appendix G..................................271 Appendix H..................................272 Appendix I..................................273 Appendix J..................................274 Appendix K..................................275 Appendix L..................................276 Appendix M..................................277 Appendix N..................................278 Appendix O..................................279 Appendix P..................................280

x LIST OF TABLES Table 2.1 Suture sizes [nSA:Nonsynthetic absorbable;nAaS:Nonabsorbable and synthetic absorbable AnA:Absorbable and nonabsorbable materials] [25]......7 Table 2.2 Suture sizes for different types of tissues................................7 Table 2.3 Suture biomaterials [86,25].............................................12 Table 2.4 Suture thermal properties [25]..........................................13 Table 2.5 Effect of diameter on tensile properties [112]...........................30 Table 2.6 Dynamic mechanical behavior of different polymers [25].................33 Table 2.7 Suture strength retention [25]...........................................37 Table 2.8 Blood pressure [12].....................................................46 Table 2.9 Default Parameters for Contact Analysis................................99 Table 4.1 Design of experiment for tissue specific barbed sutures..................133 Table 4.2 Barbed suture experiment:Tensile test.................................133 Table 4.3 Barbed suture experiment:Skin tissue pullout test......................133 Table 4.4 Barbed suture experiment:Tendon tissue pullout test..................134 Table 4.5 Prony coefficients for shear relaxation response.........................149 Table 4.6 Prony coefficients for bulk relaxation response..........................152

xi Table 4.7 Prony coefficients for tendon tissue relaxation...........................153 Table 4.8 Prony coefficients for skin tissue relaxation.............................154 Table 5.1 Comparison of simulated and experimental values.......................183

xii LIST OF FIGURES Figure 2.1 Polyglycolic acid......................................................8 Figure 2.2 Polydioxanone........................................................9 Figure 2.3 Maxon................................................................9 Figure 2.4 Monocryl.............................................................10 Figure 2.5 Nylon 6...............................................................10 Figure 2.6 Nylon 6,6.............................................................10 Figure 2.7 Polytetrafluoroethylene...............................................10 Figure 2.8 Polyethylene terephthalate............................................11 Figure 2.9 Classification chart for surgical sutures................................13 Figure 2.10 A type of knotless suture with spherical projections...................15 Figure 2.11 A knotless suturing device.............................................15 Figure 2.12 Slender barbed projections fixed on a center filament for tissue approx- imation......................................................................16 Figure 2.13 Barbed suturing apparatus............................................16 Figure 2.14 A photomicrograph of a polished surgical cat-gut suture showing grooves ..............................................................................17 Figure 2.15 Wavy filament surface a result of pulsatile polymer flow...............17 Figure 2.16 Different types projections on knotless suture designs..................18 Figure 2.17 A bi-directional suture (1) and a uni-directional suture (2).............18 Figure 2.18 Methods for creating barbs on a monofilament suture..................19 Figure 2.19 Laser cutting method for creating barb on a suture monofilament......20 Figure 2.20 Paths of blade while creating a barb on a monofilament suture........21 Figure 2.21 Monofilament suture clamping device for creating barbs...............22 Figure 2.22 Rotating disc with blades for creating barbs...........................22

xiii Figure 2.23 Rotating die for creating barbs........................................23 Figure 2.24 Suturing with bi-directional barbed suture............................24 Figure 2.25 Suturing techniques with a barbed suture.............................25 Figure 2.26 Zones at the left end of a bi-directional barbed suture.................26 Figure 2.27 Barb geometry........................................................26 Figure 2.28 Light microscopic images of barbed sutures...........................27 Figure 2.29 Core sheath structure of PDSII [B=sheath]...........................29 Figure 2.30 Suture tissue pullout test.............................................31 Figure 2.31 A soft barb unable to penetrate the tissue.............................33 Figure 2.32 Locking of barbed suture in anchor eyelet.............................36 Figure 2.33 Flexor tendon repair (A:4 strand;B:8 strand) with knotted sutures [2] 40 Figure 2.34 Suture anchor in tendon reconstruction.[99]..........................41 Figure 2.35 Suture anchor in tendon reconstruction.[105].........................42 Figure 2.36 Suture anchor in tendon reconstruction.[105].........................42 Figure 2.37 Suture with bead and anchor in bridge tendon repair.[115]...........43 Figure 2.38 Cross section of human skin (bar = 100 microns) [80].................45 Figure 2.39 Pressure expansion curve for the human abdominal skin in 10th lunar month of pregnancy [52].....................................................45 Figure 2.40 Protruding tail from suture knots made while suturing mitral valve tis- sue..........................................................................47 Figure 2.41 Suturing artery (A,B,C) and vein (D,E,F) [45]........................47 Figure 2.42 Fibrosis in vein and artery [45]........................................48 Figure 2.43 Suture anchors and tissue pullout test [88]............................52 Figure 2.44 Upper eyelid ptosis repair with knotted sutures [21]...................53 Figure 2.45 Different tissues in various organs of the human body [81].............54 Figure 2.46 Striated cardiac muscle of the heart [102].............................55

xiv Figure 2.47 Stress strain curve for cardiac muscle in persons 20 to 29 years of age [52]..........................................................................56 Figure 2.48 Cross section of a medium artery and medium vein (bar = 250 microns) [80]..........................................................................57 Figure 2.49 Cross section of an aorta (bar = 1 mm) [80]...........................57 Figure 2.50 Cross section of a medium artery (bar = 100 microns) [80]............58 Figure 2.51 Stress strain curve for arterial tissue in persons 20 to 29 years of age [52] 59 Figure 2.52 Cross section of a large vein (bar = 250 microns) [80].................60 Figure 2.53 Cross section of a medium vein (bar = 100 microns) [80]..............61 Figure 2.54 Stress strain curve of human venous tissue in persons of age group 20 to 29 years.[52]................................................................61 Figure 2.55 Cross section of larynx wall tissue (bar = 250 microns) [80]...........62 Figure 2.56 Cross section of the upper third of an oesophagus (bar = 1 mm) [80]..62 Figure 2.57 Stress strain curve of esophagus of persons 20 to 29 years of age [52]..63 Figure 2.58 Cross section of the fundus region of the stomach (bar = 250 microns) [80]..........................................................................64 Figure 2.59 Cross section of the pyloric region of the stomach (bar = 250 microns) [80]..........................................................................65 Figure 2.60 Stress strain curve of the human stomach tissue in the transverse direc- tion [52].....................................................................66 Figure 2.61 Stress strain curve of the human stomach tissue in the longitudinal di- rection [52]...................................................................66 Figure 2.62 Cross section of upper region of duodenum wall tissue (bar = 250 mi- crons) [80]...................................................................68 Figure 2.63 Cross section of lower region of duodenumwall tissue (bar =250 microns) [80]..........................................................................68 Figure 2.64 Stress strain curves for small intestine in persons between 20 to 29 years of age [52]....................................................................69 Figure 2.65 Cross section of jejunum/ileum wall tissue (bar = 250 microns) [80]...70 Figure 2.66 Stress strain curve for the large intestine of persons 20 to 29 years of age [52]..........................................................................70

xv Figure 2.67 Cross section of ureter (bar = 1 mm) [80].............................71 Figure 2.68 Stress strain curve of ureter tissue in persons between 20 to 29 years of age [52]......................................................................72 Figure 2.69 Unit vectors in 3D space..............................................75 Figure 2.70 Creep behavior in viscoelasticity......................................84 Figure 2.71 Relaxation behavior in viscoelasticity.................................85 Figure 2.72 Curve for Youngs modulus............................................85 Figure 2.73 Curves for storage and loss moduli....................................86 Figure 2.74 Crystalline and amorphous regions....................................86 Figure 2.75 Maxwell model of spring and dashpot.................................87 Figure 2.76 Voigt model of spring and dashpot....................................89 Figure 2.77 Kelvin/Standard linear model of springs and dashpot................90 Figure 2.78 Prony Series of springs and dashpots..................................91 Figure 2.79 Displacement based linear finite element method algorithm............94 Figure 2.80 SOLID187 - tetrahedral element [15]..................................97 Figure 2.81 TARGE170 - target element [15]......................................98 Figure 2.82 CONTA174 - contact element[15].....................................98 Figure 3.1 Path of suture:prototyping assembly.................................102 Figure 3.2 Central dark region (CDR)...........................................103 Figure 3.3 Take-up assembly with Reverse Lock (RL)............................104 Figure 3.4 HFS in action with blade at point zero................................109 Figure 3.5 Horizontal Force Stabilizer (HFS).....................................110 Figure 3.6 Edge profile of new blade (Surgical skin graft blade)..................111 Figure 3.7 Critical cut point (CCP) at zero contact..............................112 Figure 3.8 Concaving phenomenon in suture.....................................116 Figure 3.9 Elastic Tensioner (ET)................................................116

xvi Figure 3.10 A fractured barb......................................................117 Figure 3.11 Adjustable guide......................................................118 Figure 3.12 Steps in blade preparation............................................119 Figure 3.13 A surgical skin graft blade super-glued to metal plate.................120 Figure 3.14 Damaged blade profile (carpet blade).................................121 Figure 3.15 The base fixture and base-to-MTS connector assembly................122 Figure 3.16 Barbed Suture Imaging Clamp (BSIC)................................124 Figure 3.17 Barb geometry measurement in Matlab...............................127 Figure 3.18 A good quality barb..................................................129 Figure 3.19 Chipped suture due to unexpected blade contact......................130 Figure 3.20 Barb bent due to failure to release ET-2 at take-up...................131 Figure 3.21 A dead barb with no functional tip....................................131 Figure 4.1 Specimen preparation for skin and tendon tissue pullout test..........135 Figure 4.2 Threading the barb into the tissue for preparing the pullout specimen.136 Figure 4.3 Barb suture specimen mounting for tensile test using capstan clamping effect........................................................................138 Figure 4.4 Barb tip glued to rounded wire tip....................................139 Figure 4.5 Barb tip glued to a pointed barbed wire tip...........................139 Figure 4.6 Pure loading of single barb............................................140 Figure 4.7 Specimen mounted ready for a skin tissue pullout test.................141 Figure 4.8 Specimen mounted ready for a tendon tissue pullout test..............142 Figure 4.9 Suture specimen geometry for measuring shear relaxation modulus....146 Figure 4.10 Suture mounting for cutting specimens................................147 Figure 4.11 Method of cutting suture specimen....................................148 Figure 4.12 Calculating shear relaxation modulus for suture monofilament.........148 Figure 4.13 Measuring bulk relaxation modulus of monofilament sutures...........150

xvii Figure 4.14 Calculating shear relaxation modulus for suture monofilament.........151 Figure 4.15 Unbarbed suture bulk relaxation modulus in axial direction...........152 Figure 4.16 Human tendon tissue relaxation modulus [7]..........................153 Figure 4.17 Porcine skin tissue relaxation modulus [69]...........................154 Figure 4.18 Solid model of single barb for point loading of barb tip................156 Figure 4.19 Lines and areas of a single barbed suture..............................156 Figure 4.20 Meshed barb:150 o cut angle & 0.12mm cut depth....................158 Figure 4.21 Meshed barb:160 o cut angle & 0.12mm cut depth....................158 Figure 4.22 Meshed barb:170 o cut angle & 0.12mm cut depth....................159 Figure 4.23 Straight pullout of single barb anchored in tissue......................160 Figure 4.24 Lines and areas of a anchored single barb in tissue....................161 Figure 4.25 Straight pullout of single barb anchored in tissue......................161 Figure 4.26 Straight pullout test of single barb anchored in tissue.................162 Figure 4.27 Magnified view:Anchored tissue......................................163 Figure 4.28 Straight pullout test of single barb anchored in tissue.................164 Figure 4.29 Target:Barbed suture [TARGE170 elements].........................165 Figure 4.30 Contact:Tissue [CONTA174 elements]................................166 Figure 4.31 A ’Geomcirc’ barbed suture...........................................167 Figure 4.32 A meshed ’Geomcirc’ barbed suture...................................167 Figure 5.1 150 o at 0.07mm........................................................170 Figure 5.2 150 o at 0.12mm........................................................170 Figure 5.3 150 o at.18mm........................................................170 Figure 5.4 160 o at 0.07mm........................................................171 Figure 5.5 160 o at 0.12mm........................................................171 Figure 5.6 160 o at.18mm........................................................171 Figure 5.7 170 o at 0.07mm........................................................171

xviii Figure 5.8 170 o at 0.12mm........................................................171 Figure 5.9 170 o at.18mm........................................................171 Figure 5.10 Mean±S.E.for suture diameter.......................................172 Figure 5.11 Mean±S.E.for barb cut angle.........................................173 Figure 5.12 Mean±S.E.for barb cut depth........................................174 Figure 5.13 Mean±S.E.for elongation % at peak tensile load......................175 Figure 5.14 Profile of a barbed and unbarbed suture tensile curve.................176 Figure 5.15 Mean±S.E.for peak tensile load......................................177 Figure 5.16 Barbed suture peak tensile load [Mean±S.E.]..........................178 Figure 5.17 Peak tensile skin tissue pullout load (mean±S.E.).....................179 Figure 5.18 Chart.................................................................179 Figure 5.19 Peak tensile tendon tissue pullout load (mean±S.E.)..................181 Figure 5.20 Chart.................................................................181 Figure 5.21 Metal wire barb tip pull experimental curve...........................184 Figure 5.22 150 o at 0.07mm........................................................185 Figure 5.23 150 o at 0.12mm........................................................185 Figure 5.24 150 o at.18mm........................................................185 Figure 5.25 160 o at 0.07mm........................................................185 Figure 5.26 160 o at 0.12mm........................................................185 Figure 5.27 160 o at.18mm........................................................185 Figure 5.28 170 o at 0.07mm........................................................185 Figure 5.29 170 o at 0.12mm........................................................185 Figure 5.30 170 o at.18mm........................................................185 Figure 5.31 Barb tip displacement at point pressure load..........................186 Figure 5.32 Effect of cut angle on cut line stresses at 0.07mm cut depth...........187 Figure 5.33 Effect of cut angle on cut line stresses at 0.12mm cut depth...........187

xix Figure 5.34 Effect of cut angle on cut line stresses at 0.18mm cut depth...........188 Figure 5.35 Effect of cut depth on cut line stresses at 150 o cut angle...............189 Figure 5.36 Effect of cut depth on cut line stresses at 160 o cut angle...............189 Figure 5.37 Effect of cut depth on cut line stresses at 170 o cut angle...............190 Figure 5.38 Displacement (UZ) of new and original designs........................191 Figure 5.39 Increased resiliency of new design.....................................191 Figure 5.40 SYZ:New[c-150-07-10];Original[150-07] at 0.07mm...................192 Figure 5.41 SYZ:New[c-150-07-10];Original[150-07] at 0.12mm...................193 Figure 5.42 SYZ:New[c-150-07-10];Original[150-07] at 0.18mm...................193 Figure 5.43 ’Geomcirc’:Vector plot(displacement) [ca:160 o .cd;0.07mm]...........194 Figure 5.44 Original:Vector plot(displacement)[ca:160 o .cd;0.07mm]..............195 Figure 5.45 ’Geomcirc’:Peeling stress (SYZ) (ca:160 o .cd;0.07mm)................196 Figure 5.46 Original:Peeling stress (SYZ) (ca:160 o .cd;0.07mm)..................196 Figure 5.47 Tendon tissue pullout test simulation.................................198 Figure 5.48 UZ:Tendon tissue & barb (ca:150 o .cd;0.07mm)......................199 Figure 5.49 Skin tissue pullout test simulation....................................200 Figure 5.50 UZ:Skin tissue & barb (ca:150 o .cd;0.07mm).........................200 Figure 5.51 UY:Tendon tissue under barb (ca:150 o .cd;0.07mm)..................201 Figure 5.52 UY:Skin tissue under barb (ca:150 o .cd;0.07mm).....................202 Figure 5.53 Simulation comparison:Skin vs.Tendon tissue........................203 Figure 5.54 SYZ:skin [s-160-07] & tendon [t-160-07](cut depth 0.07mm)...........203 Figure 5.55 SYZ:skin [s-160-07] & tendon [t-160-07](cut depth 0.18mm)...........204 Figure 5.56 Displacement - symmetry-cut side (ca:150 o .cd;0.07mm)...............205 Figure 5.57 Direction of displacement - LEFT side (ca:150 o .cd;0.07mm)..........205 Figure 5.58 Wake of the barb (ca:150 o .cd;0.07mm)...............................206 Figure 5.59 Barb fracture:Tensile & bending effect (ca:150 o .cd;0.18mm).........207

xx Figure 5.60 Tendon tissue behavior in a pullout test (ca:150 o .cd;0.07mm).........208 Figure 5.61 Tendon tissue behavior in a pullout test (ca:150 o .cd;0.07mm).........209 Figure 5.62 Tendon tissue behavior in a pullout test (ca:150 o .cd;0.07mm).........210 Figure 7.1 Curved suture........................................................218 Figure 7.2 Meshed curved suture.................................................218 Figure 7.3 Magnified view of meshed barb in curved suture.......................219 Figure 7.4 A copper metal barb..................................................221 Figure 0.5 Variation in diameter for 150 o .........................................267 Figure 0.6 Variation in diameter for 160 o .........................................267 Figure 0.7 Variation in diameter for 170 o .........................................267 Figure 0.8 Variation in cut angle 150 o ............................................268 Figure 0.9 Variation in cut angle 160 o ............................................268 Figure 0.10 Variation in cut angle 170 o ............................................268 Figure 0.11 Variation in cut depth 150 o ...........................................269 Figure 0.12 Variation in cut depth 160 o ...........................................269 Figure 0.13 Variation in cut depth 170 o ...........................................269 Figure 0.14 150 o at 0.07mm........................................................270 Figure 0.15 150 o at 0.12mm........................................................270 Figure 0.16 150 o at.18mm........................................................270 Figure 0.17 160 o at 0.07mm........................................................270 Figure 0.18 160 o at 0.12mm........................................................270 Figure 0.19 160 o at.18mm........................................................270 Figure 0.20 170 o at 0.07mm........................................................270 Figure 0.21 170 o at 0.12mm........................................................270 Figure 0.22 170 o at.18mm........................................................270 Figure 0.23 150 o at 0.07mm........................................................271

xxi Figure 0.24 150 o at 0.12mm........................................................271 Figure 0.25 150 o at.18mm........................................................271 Figure 0.26 160 o at 0.07mm........................................................271 Figure 0.27 160 o at 0.12mm........................................................271 Figure 0.28 160 o at.18mm........................................................271 Figure 0.29 170 o at 0.07mm........................................................271 Figure 0.30 170 o at 0.12mm........................................................271 Figure 0.31 170 o at.18mm........................................................271 Figure 0.32 150 o at 0.07mm........................................................272 Figure 0.33 150 o at 0.12mm........................................................272 Figure 0.34 150 o at.18mm........................................................272 Figure 0.35 160 o at 0.07mm........................................................272 Figure 0.36 160 o at 0.12mm........................................................272 Figure 0.37 160 o at.18mm........................................................272 Figure 0.38 170 o at 0.07mm........................................................272 Figure 0.39 170 o at 0.12mm........................................................272 Figure 0.40 170 o at.18mm........................................................272 Figure 0.41 150 o at 0.07mm........................................................273 Figure 0.42 150 o at 0.12mm........................................................273 Figure 0.43 150 o at.18mm........................................................273 Figure 0.44 160 o at 0.07mm........................................................273 Figure 0.45 160 o at 0.12mm........................................................273 Figure 0.46 160 o at.18mm........................................................273 Figure 0.47 170 o at 0.07mm........................................................273 Figure 0.48 170 o at 0.12mm........................................................273 Figure 0.49 170 o at.18mm........................................................273

xxii Figure 0.50 150 o at 0.07mm........................................................274 Figure 0.51 150 o at 0.12mm........................................................274 Figure 0.52 150 o at.18mm........................................................274 Figure 0.53 160 o at 0.07mm........................................................274 Figure 0.54 160 o at 0.12mm........................................................274 Figure 0.55 160 o at.18mm........................................................274 Figure 0.56 170 o at 0.07mm........................................................274 Figure 0.57 170 o at 0.12mm........................................................274 Figure 0.58 170 o at.18mm........................................................274 Figure 0.59 150 o at 0.07mm........................................................275 Figure 0.60 150 o at 0.12mm........................................................275 Figure 0.61 150 o at.18mm........................................................275 Figure 0.62 160 o at 0.07mm........................................................275 Figure 0.63 160 o at 0.12mm........................................................275 Figure 0.64 160 o at.18mm........................................................275 Figure 0.65 170 o at 0.07mm........................................................275 Figure 0.66 170 o at 0.12mm........................................................275 Figure 0.67 170 o at.18mm........................................................275 Figure 0.68 150 o at 0.07mm........................................................276 Figure 0.69 150 o at 0.12mm........................................................276 Figure 0.70 150 o at.18mm........................................................276 Figure 0.71 160 o at 0.07mm........................................................276 Figure 0.72 160 o at 0.12mm........................................................276 Figure 0.73 160 o at.18mm........................................................276 Figure 0.74 170 o at 0.07mm........................................................276 Figure 0.75 170 o at 0.12mm........................................................276

xxiii Figure 0.76 170 o at.18mm........................................................276 Figure 0.77 150 o at 0.07mm........................................................277 Figure 0.78 150 o at 0.12mm........................................................277 Figure 0.79 150 o at.18mm........................................................277 Figure 0.80 160 o at 0.07mm........................................................277 Figure 0.81 160 o at 0.12mm........................................................277 Figure 0.82 160 o at.18mm........................................................277 Figure 0.83 170 o at 0.07mm........................................................277 Figure 0.84 170 o at 0.12mm........................................................277 Figure 0.85 170 o at.18mm........................................................277 Figure 0.86 150 o at 0.07mm........................................................278 Figure 0.87 150 o at 0.12mm........................................................278 Figure 0.88 150 o at.18mm........................................................278 Figure 0.89 160 o at 0.07mm........................................................278 Figure 0.90 160 o at 0.12mm........................................................278 Figure 0.91 160 o at.18mm........................................................278 Figure 0.92 170 o at 0.07mm........................................................278 Figure 0.93 170 o at 0.12mm........................................................278 Figure 0.94 170 o at.18mm........................................................278 Figure 0.95 150 o at 0.07...........................................................279 Figure 0.96 150 o at 0.12...........................................................279 Figure 0.97 150 o at.18............................................................279 Figure 0.98 160 o at 0.07...........................................................279 Figure 0.99 160 o at 0.12...........................................................279 Figure 0.100160 o at.18............................................................279 Figure 0.101170 o at 0.07...........................................................279

xxiv Figure 0.102170 o at 0.12...........................................................279 Figure 0.103170 o at.18............................................................279 Figure 0.104150 o at 0.07...........................................................280 Figure 0.105150 o at 0.12...........................................................280

1 Chapter 1 Introduction 1.1 Background The successful performance of a surgical suture has until recently depended on the clinicians’ ability to tie an efficient and secure knot.In fact suture performance has inevitably been closely associated with knot security.However,from time to time clin- icians have experimented with various types of knotless sutures,which,if mechanically secure,can provide certain advantages over the traditional knotted suture. One type of knotless suture is the ”barbed” suture,in which protruding barbs are placed in one or two directions along the length of a monofilament suture [79].In vitro studies have already reported incorporating image analysis to measure the barb geometry [82],comparing the tissue holding capacity of a barbed suture and a knotted suture [82,83],and the effect of suture polymer microstructure on barb tissue holding capacity in a suture tissue pullout test [86].In addition,in vivo animal studies have described the biostability of such sutures when exposed to body fluids [26].In fact barbed sutures have been found to be clinically successful in subdermal wound closure and in tendon repair in human patients.Currently they are used successfully by cosmetic surgeons such as Dr.Gregory Ruff,to undertake facelift and masklift procedures It would therefore be interesting to see if we could use barbed sutures for the repair and apposition of other organs and tissues having a wide range of different mechanical properties,and finding how this question might be answered is the ultimate goal of this study.For example,the geometric shape,frequency,alignment and sequence of barbs for a particular material may be optimized for use with skin tissue.However this same barbed design may not be optimal for a suture to be used in tendon tissue

2 or fatty tissue.It is therefore of great interest in this study to attempt to optimize the barb geometry and frequency for each type of suture material in each type of tissue. Finite element analysis is an important tool to do virtual prototyping and testing of the new designs and geometries of barbed sutures.Once the FEA model is optimized in the virtual environment,then manufacturing of that particular type of suture for a given tissue can be undertaken.This approach in the design and development of new tissue speicific variants of barbed sutures will improve the efficiency of the research and development process. 1.2 Objectives The primary objectives of this study are: 1.to design and establish a new prototyping method that will prepare barbed sutures with precisely controlled geometries and frequencies. 2.to quantify the effect of different independent variables in the geometry of a single barb,such as cut depth and cut angle,on the barb’s tissue holding capacity. 3.to create a 3D solid model for a single barb and run a finite element analysis simulation using Ansys software using point pressure loading at the tip of the barb and compare the results with the experimental result where the barb tip is pulled by metal wire.Optimize and validate the model so as to achieve a close approximation to and prediction of the experimental result. 4.to create and analyse 3D solid models so as to study the effect of varying cut angle and cut depth on the displacement under point pressure loading at the tip of the barb 5.to create and analyse 3D solid models of virtual suture/tissue pullout tests for skin and tendon tissue 6.to develop and test a virtual prototype of a new and improved design of barbed surgical suture The steps to achieve the above objectives are listed below: • experimentally determine the stress-strain and stress relaxation behavior of monofil- ament sutures under static conditions

3 • use curve fitting in Ansys to find the Prony series constants fromthe experimental data • create barbs with different designs and geometries for use with various tissue types with varying properties.Note some experimental data for tissue properties have already been reported in the literature • run experiments to find the tissue holding capacity of the specific design for a particular type of tissue or tissue simulant • undertake a solid model analysis of various barb designs • use finite element analysis software ANSYS to simulate the effect of loading on a single barb • compare the simulation results with experimental results with a view to validating the FEA model • analyse the results for barb deformation and areas of stress concentration with a view to optimizing and validating the design of the barb geometry suitable for particular tissue types. 1.3 Outline of Thesis This thesis is written in a series of chapters.The following list indicates the contents of each chapter: 1.Introduction:Describes in general the importance and relevance of barbed su- ture technology in health care.Lists the primary objectives of the study. 2.Review of Literature:Describes various types of knotless sutures,anchors, staples and methods of making the same.The clinical literature is also reviewed and examples of surgeries where barbed sutures have potential advantages are listed. 3.Barbed Suture Prototyping:Describes in detail the method of prototyping barbed suture how the equipment was developed for the preparation of barbed sutures for the current project

Full document contains 319 pages
Abstract: The project titled 'Prototyping and Finite Element Analysis of Tissue Specific Barbed Sutures' is focussed on understanding the relationship between barb geometry and mechanical behavior of barbed sutures. In this study size '0' polypropylene monofilament sutures of diameter 0.4mm were used for creating barbs at 150°, 160° and 170° cut angles and 0.07, 0.12 and 0.18mm cut depths. A new prototyping method was developed to create barbed sutures with precisely controlled geometries whichd used tMTS tensile testing machine to control cut depth. The cut samples were then characterized by image analysis to assess the reproducibility and the variability associated with the barbs geometric dimensions. Tensile testing and stress and bulk relaxation experiments were performed to obtain viscoelastic constants for finite element modeling. An experiment was run to quantify the peeling properties of a barb under point-pressure load by attaching a metal wire to the end of the barb. Suture/tissue pullout experiments were also performed using bovine tendon and porcine skin tissues. The finite element simulation of the point-pressure loading of a barb tip in ANSYS was validated by experimental results of the same materials by a margin of only 4%. Three sets of FEA simulations were then performed for each of the nine blocks of combination of barb geometries. The same three levels of cut angle and three levels of cut depth were selected. In addition point-pressure loading simulations were run and experimental suture/tissue pullout tests were performed on tendon and skin tissues. The experimental results revealed that since tendon tissue has a higher modulus than skin it needs a more rigid barb to penetrate and anchor into the surrounding tissue. A cut angle of 150° and 0.18mm cut depth are recommended. On the other hand for the softer skin tissue a cut angle of 170 degrees and 0.18 mm cut depth provided a more flexible barb that gives superior skin tissue anchoring. The simulations helped identify the areas of stress concentration. The cut line at the base of the cut appears to be the weakest part of the barb. So the geometry or design should be modified so that the stresses generated are lower. A new design with a circular cut line has been virtually prototyped and tested in ANSYS. This new and improved design helps to redistribute the stresses along the barb and its cut line so that peeling is initiated at higher stresses and improved anchoring performance.