Contact Mechanics and Failure Modes of Compliant Polymeric Bearing Materials For Knee Cartilage Replacement A Thesis Submitted to the Faculty Of Drexel University By Mariya Shabbir Tohfafarosh in partial fulfillment of the requirements for the degree Of Doctor of Philosophy September 2016 © Copyright 2017 Mariya Shabbir Tohfafarosh. All Rights Reserved. ii And, when you want something, all the universe conspires in helping you to achieve it. - Paulo Coelho, The Alchemist iii Acknowledgements It takes a whole village to cultivate a Ph.D. I want to thank my advisor and mentor, Dr. Steven Kurtz, who placed faith in my abilities and provided valuable insights into my journey of exploring the convoluted world of finite element modeling and material failure analysis. I am grateful to my committee members, Dr. Sriram Balasubramariam, Dr. Michele Marcolongo, Dr. Margaret Wheatley, Dr. Judd Day and Dr. Rahmim Seliktar, for asking critical questions, providing constructive criticism and giving direction to improve this work. I also appreciate Dr. Doruk Baykal for being a great mentor, and for teaching me how to be a good researcher over friendly banters. Thanks to Ryan Siskey for his wisdom and accommodating my testing needs, and Dr. Jonathan Kiel for an insightful discussion about the fascinating world of polymer science. Thank you, Dr. Kevin Mansmann, for financially supporting my work and for giving me first-hand experience of the intricacy of human-centric product design. This work would not have been possible without the never-ending discussions, constant support, and encouragement from my friends and fellow Implant Research Center members – Daniel MacDonald, Josa Hanzlik, Sai Veruva, Sevi Kocagoz, James Peters, Genymphas Higgs and Christina Arnholt – you guys and gals made this journey bearable and memorable! Last but not the least, this expedition would not have been possible without the endless love and emotional support of my parents, my brother, my sister-in-law and my niece. iv Special thanks to my love, Mohammed, for helping me retain my sanity and reminding me to laugh during this interesting life-experiment of “pursuing a doctorate.” v Table of Contents LIST OF TABLES ............................................................................................................ IX LIST OF FIGURES ............................................................................................................ X ABSTRACT .................................................................................................................... XIII CHAPTER 1 : INTRODUCTION .......................................................................................1 HUMAN KNEE AND ARTICULAR CARTILAGE .................................................................... 1 OSTEOARTHRITIS ............................................................................................................. 2 CURRENT TREATMENTS ................................................................................................... 3 Total Knee Arthroplasty .............................................................................................. 3 Partial Knee Replacement ........................................................................................... 4 CURRENT ARTHROPLASTY MATERIALS ........................................................................... 5 COMPLIANT ARTHROPLASTY MATERIAL CANDIDATES .................................................... 6 Polyurethane/Polycarbonate Urethane ....................................................................... 7 Hydrogels................................................................................................................... 10 CHALLENGES IN DEVELOPMENT OF SYNTHETIC CARTILAGE IMPLANT .......................... 13 KNEE BIOMECHANICS .................................................................................................... 14 RESEARCH OVERVIEW ................................................................................................... 16 SPECIFIC AIMS................................................................................................................ 17 CHAPTER 2 : LITERATURE REVIEW – KNEE IMPLANT DESIGN PARAMETERS AND ARTHROPLASTY MATERIAL FAILURE THEORIES ......................................20 INTRODUCTION ............................................................................................................... 20 CURRENT IMPLANT DESIGNS .......................................................................................... 22 vi COMPLIANT BEARING MATERIAL IMPLANT DESIGN ...................................................... 24 COMPLIANT MATERIAL FAILURE CRITERIA AND MODES ............................................... 35 RESEARCH GAP AND GOAL OF THESIS ........................................................................... 40 CHAPTER 3 : EFFECT OF RADIATION STERILIZATION ON CHEMICAL, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF A NOVEL HYDROGEL.42 ABSTRACT ...................................................................................................................... 42 INTRODUCTION ............................................................................................................... 42 MATERIALS & METHOD ................................................................................................. 45 Swell Ratio Evaluation .............................................................................................. 45 Mechanical Testing.................................................................................................... 46 Finite Element Analysis ............................................................................................. 46 Chemical Evaluation ................................................................................................. 49 Wear Testing .............................................................................................................. 49 RESULTS ......................................................................................................................... 51 Material Model Verification ...................................................................................... 51 Chemical Evaluation ................................................................................................. 53 Tribological Properties ............................................................................................. 54 DISCUSSION .................................................................................................................... 57 CONCLUSION .................................................................................................................. 59 CHAPTER 4 : EFFECT OF CONFORMITY, THICKNESS AND MATERIAL PROPERTIES ON THE CONTACT MECHANICS OF COMPLIANT POLYMERIC MATERIALS FOR USE IN KNEE ARTHROPLASTY ..................................................61 ABSTRACT ...................................................................................................................... 61 INTRODUCTION ............................................................................................................... 62 vii MATERIALS & METHOD ................................................................................................. 66 Mechanical Testing.................................................................................................... 66 Model Construction and Validation .......................................................................... 67 Parametric Modeling ................................................................................................. 69 RESULTS ......................................................................................................................... 70 Mechanical Testing.................................................................................................... 70 Model Validation ....................................................................................................... 71 Parametric Evaluation .............................................................................................. 72 DISCUSSION .................................................................................................................... 84 CONCLUSION .................................................................................................................. 87 ACKNOWLEDGEMENT ..................................................................................................... 88 CHAPTER 5 : MECHANICAL FAILURE MODALITY OF COMPLIANT ARTHROPLASTY MATERIALS UNDER PHYSIOLOGICALLY RELEVANT LOADING CONDITIONS ................................................................................................89 ABSTRACT ...................................................................................................................... 89 INTRODUCTION ............................................................................................................... 90 MATERIALS & METHOD ................................................................................................. 92 Uniaxial Tensile Test to Failure ................................................................................ 93 Unconfined Compression Test ................................................................................... 93 Plane Strain Compression Test ................................................................................. 94 RESULTS ........................................................................................................................