© 2018 Vrushali Bhagat ALL RIGHTS RESERVED POLY(ESTER UREA) BASED BIOMIMETIC BONE AND SOFT TISSUE ADHESIVES A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Vrushali Bhagat May, 2018 POLY(ESTER UREA) BASED BIOMIMETIC BONE AND SOFT TISSUE ADHESIVES Vrushali Bhagat Dissertation Approved: Accepted: Advisor Department Chair Dr. Matthew L. Becker Dr. Coleen Pugh Committee Chair Dean of the College Dr. Ali Dhinojwala Dr. Eric J. Amis Committee Member Dean of the Graduate School Dr. Chrys Wesdemiotis Dr. Chand Midha Committee Member Date Dr. Mesfin Tsige Committee Member Dr. Bryan Vogt ii ABSTRACT Sutures and staples are an integral part of surgeries and also the gold standard for surgical closure techniques. Additionally, in the case of orthopedic surgeries, metallic implants like plates, pins or screws are usually inserted as bone grafts. However, these techniques are quite invasive in nature, may cause wound dehiscence, secondary tissue damage, microbial infection, poor cosmetic outcome and more importantly discomfort to the patient. In some cases, the patient has to undergo another surgery for removal or replacement of sutures or bone grafts. These shortcomings have led to an urgent need to develop alternative, less invasive surgical closure techniques. Use of tissue adhesives for wound closure is an attractive alternative over the invasive methods owing to ease of preparation and application, strong adhesion and gradual degradation with tissue reconstruction. However, their toxic degradation products and potentially harmful cross- linking strategies have limited their medical applications. Recently, biomimetic adhesives have become a popular choice for application as tissue adhesives. Biomimetic adhesives are inspired from examples of adhesion in nature like mussels, sandcastle worms, barnacles, caddisflies, geckos and spiders to name a few. The adhesion characteristics and adhesive properties of mussels are of particular interest due to their strong wet and reversible adhesion, steadfast hold under variation in temperature, pH and water currents. The mussel adhesive is rich in polyphenolic protein - 3,4- dihydroxyphenylalanine (DOPA). The catechol functionality in DOPA is assumed to be iii the source of strong underwater adhesion in mussels. In this work, we have synthesized a catechol functionalized ethanol soluble poly(ester urea) (poly(CA-Ser-co-Leu-co-PPG) copolymer for soft tissue application. Incorporation of 20 mol% PPG units in the polymer backbone facilitates ethanol solubility making these adhesives clinically relevant. The polymer was characterized using NMR, IR and UV-VIS spectroscopy to confirm its structure and catechol content. The physical properties of the polymer like Tg, Td, Mn, Mw and ÐM were characterized by DSC, TGA and SEC respectively. The lap shear adhesion strength of this polymer on aluminum adherends was ~ 3.2 ± 0.8 MPa after cross-linking with tetrabutylammonium periodate. On wet porcine skin, the adhesion strength was ~ 10.6 ± 2.1 kPa after 4 h of curing for a catechol:crosslinker = 10:1 with minimal to no toxicity. Moreover, the adhesion strength on wet porcine skin was much stronger than Tisseel – commercial fibrin glue. Caddisflies are aquatic organisms that spin their own adhesive silk underwater to form protective casing, capture prey and for locomotion. Caddisfly adhesive silk is comprised of H-fibroin and L-fibroin in a 1:1 ratio and has abundant divalent cations like Ca2+. The H-fibroin silk is heavily phosphorylated with repeating pSXn units where pS is phosphoserine and X is a more hydrophobic amino acid like valine or isoleucine. The phosphate groups play a role in underwater adhesion in addition to interacting with the divalent cations to impart stiffness and tensile strength to the fiber. Phosphate groups also have a strong electrostatic interaction with the Ca2+ on the bone surface which aids in promoting bone adhesion. To test this hypothesis, we synthesized phosphate functionalized poly(ester urea) – poly(pSer-co-Val) with 2% and 5% phosphate functionality. As confirmed via 1H, 13C, 31P NMR and ATR-IR spectroscopy. The iv physical properties of the polymers were characterized using DSC, TGA and SEC. The maximum lap shear adhesion strength on an aluminum adherend was 1.17 ± 0.19 MPa and 439 ± 203 kPa on wet bovine bone after cross-linking with Ca2+. The adhesion strength on bovine bone was comparable to the commercially available bone cement. These polymeric mimics are degradable, non-toxic and soluble in a clinically relevant solvent which sets them apart from the commercial options. v DEDICATION I would like to dedicate this work to my family – mom, dad, sister and brother-in-law for their patience and unending support. vi ACKNOWLEDGEMENT I would like to take this opportunity to express my gratitude towards people who have supported and helped me throughout this wonderful journey. I would first like to thank my advisor Prof. Matthew L. Becker for giving me excellent opportunities, his cooperation and valuable guidance during my graduate research. His constant support, creative ideas and profound knowledge have instilled me with a passion for my research. I would also like to extend my gratitude towards my committee members: Prof. Ali Dhinojwala, Prof. Mesfin Tsige, Prof. Chrys Wesdemiotis, Prof. Alamgir Karim and Prof. Bryan Vogt for their time, valuable suggestions, meaningful discussions and constructive ideas. I want to thank Dr. Jinjun Zhou for helping me kick-start my research and for being an incredible mentor during my graduate journey. I am very thankful to the Becker Research Group for their friendship and support which made this journey a smooth ride. I would also like to take this opportunity to thank my friends in Akron who have been like my extended family. With their love and encouragement I was able to stay committed to my goal. I would also like to thank my niece for cheering me up with her beautiful smiles and inspiring me every day to achieve my dream. Finally, I would like to convey my special thanks to my parents, sister and brother-in-law for constantly believing in me. Without their love, prayers and unconditional support I would not have achieved this feat. vii TABLE OF CONTENTS Page LIST OF TABLES .............................................................................................................. x LIST OF FIGURES ........................................................................................................... xi LIST OF SCHEMES ....................................................................................................... xxii CHAPTER I. INTRODUCTION .................................................................................................. 1 1.1. FIBRIN GLUE ............................................................................................ 4 1.2. GELATIN-RESORCINOL-FORMALDEHYDE/GLUTARALDEHYDE GLUE (GRFG) ............................................................................................ 7 1.3. CYANOACRYLATE GLUE ................................................................... 10 1.4. POLYSACCHARIDE, POLYPEPTIDE OR POLYMERIC ADHESIVES ................................................................................................................... 13 1.5. POLY(ETHYLENE GLYCOL) (PEG) BASED HYDROGEL ADHESIVES ............................................................................................ 32 1.6. BIOMIMETIC TISSUE ADHESIVES ..................................................... 40 II. MATERIALS AND INSTRUMENTS ................................................................ 73 2.1. MATERIALS ............................................................................................ 73 2.2. INSTRUMENTS....................................................................................... 74 III. POLY(ESTER UREA) BASED ADHESIVES: IMPROVED DEPLOYMENT AND ADHESION BY INCORPORATION OF POLY(PROPYLENE GLYCOL) SEGMENTS ......................................................................................................... 78 3.1. OUTLINE ................................................................................................. 78 viii 3.2. INTRODUCTION .................................................................................... 79 3.3. EXPERIMENTAL SECTION .................................................................. 81 3.4. RESULTS AND DISCUSSION ............................................................... 87 3.5. CONCLUSION ......................................................................................... 98 IV. CADDISFLY INSPIRED PHOSPHORYLATED POLY(ESTER UREA)- BASED DEGRADABLE BONE ADHESIVES ................................................ 100 4.1. OUTLINE ............................................................................................... 100 4.2. INTRODUCTION .................................................................................. 101 4.3. EXPERIMENTAL SECTION ................................................................ 103 4.4. RESULTS AND DISCUSSION ............................................................. 114 4.5. CONCLUSION ....................................................................................... 128 V. SUMMARY AND FUTURE SCOPE ............................................................... 130 APPENDIX ....................................................................................................................