The synthesis and development of novel, easily processable poly (n-isopropylacrylamide)-based hyrdogels. BOYES, Victoria L. Available from Sheffield Hallam University Research Archive (SHURA) at: http://shura.shu.ac.uk/19381/ This document is the author deposited version. You are advised to consult the publisher's version if you wish to cite from it. Published version BOYES, Victoria L. (2012). The synthesis and development of novel, easily processable poly (n-isopropylacrylamide)-based hyrdogels. Doctoral, Sheffield Hallam University (United Kingdom).. Copyright and re-use policy See http://shura.shu.ac.uk/information.html Sheffield Hallam University Research Archive http://shura.shu.ac.uk 1 L.ceimiiiy ana inTQrmation Services I I Adsetts Centre, City Campus I | Sheffield S 1 1VVD _ _ | 102 019 751 X REFERENCE ProQuest Number: 10694262 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. 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Box 1346 Ann Arbor, Ml 48106- 1346 The Synthesis and Development of Novel, Easily Processable Poly{ N- Isopropylacrylamide)- Based Hydrogels Victoria Boyes A thesis submitted in partial fulfilment of the requirements of Sheffield Hallam University for the degree of Doctor of Philosophy September 2012 Collaborating Organisation: Smith & Nephew Extruded Films Declaration The work described in this thesis was carried out by the author in the Materials and Engineering Research Institute at Sheffield Hallam University, between October 2008 and August 2012. The author declares that this work has not been submitted for any other degree. The work is original except where acknowledged by reference. Author: I C^O'S/q (Victoria Boyes) Director of Studies: (Dr. Christopher Sammon) Acknowledgements First and foremost, I'd like to thank Dr. Chris Sammon for his guidance, advice, expertise, supervision and invaluable and copious words of wisdom throughout my PhD. I'd like to thank him for giving me this opportunity to develop as an academic and as a person. This experience has positively impacted my life beyond measure. I'd like to extend my thanks to my additional supervisor, Professor Chris Breen for his scientific input and continuous support and guidance. I feel very fortunate to have had such an influential supervisory team. I would like to thank Smith & Nephew Extruded Films and the HEFCE for funding this project. I'd like to extend specia] thanks to Jonathan Foulkes at SNEF for granting me this opportunity, for which I am eternally grateful. Special thanks must go to those who have kindly offered their assistance in some of the characterisation techniques used in this thesis - Professor Stephen Rimmer, Professor Stephen Armes, Lee Fielding and Melanie Hannah at the University of Sheffield, and Dr. Helen Willcock at the University of Warwick. I'd also like to thank all of the staff and students at MERI past and present, particularly Michael Barwood, who has been my confidante and co-conspirator here since day one. Our lengthy chats have often been an uplifting source of inspiration; you really have been a most excellent colleague and lfiend. Also, in no particular order, Francis Clegg, Khairuddin, Hakan Keles, Tom Smallwood, Kerstin Mader, Marianne Labet, Subodh Sabnis, Prakash Muthodoss, Wioletta Jablonska, Corrie Houton, Gillian Hill and Rachael Toogood. You are all exceptional people and I am grateful for the contribution you've all made to my experience at MERI. I'd like to thank my family - my parents, my sisters Kimberley and Kayleigh and my brothers James, Christopher, Jordan and Keiron, also the next generation of "Boyesies"- my handsome nephews Sebastian and Reuben, who are without doubt destined for great things. Thank you so much to my friends, those who have both offered words of encouragement and rolled eyes at me over the years through the elation and despair, and for making the last 4 years the best of my life. Extra special thanks to Emmanuel "Eman" Onafowokan, without whom this story would never have begun. Thank you for your encouragement and belief in me from the very beginning. I dedicate my thesis to my big sister Kerrie and my dad. I don't know what I'd have done without your love, support, and occasional nudge in the right direction. Thanks for believing in me and for the words of encouragement when I needed them most. Vicky B III Abstract This work describes the invention of a synthetic method which allows a fully-reacted PNIPAM/ clay nanocomposite system to remain a watery liquid until it is cooled to a predetermined temperature. Beyond this temperature, the polymer/ clay precursor hydrogel liquid (PCPH) spontaneously forms a cross-linked hydrogel that does not re-liquefy upon re-heating, but instead, possesses all of the highly utilisable stimuli-responsive properties typical of PNIPAM-based nanocomposite hydrogels synthesised in situ. This novel methodology simultaneously addresses issues including cytotoxicity, processability, injectability, cross-linking and mechanical stability. In addition, PCPH synthesis requires no specialist equipment, inexpensive and basic components typical of cross-linked hydrogels (water, monomer, clay and initiator), requires no purification steps and can be maintained as a fully-reacted liquid at evaluated temperatures for up to several weeks with no apparent loss of eventual functionality. The ability to create a fully polymerised hydrogel polymer with a liquid intermediate state has allowed the incorporation of biologically active dopants which can be dispersed and distributed homogeneously throughout the matrix prior to "phase transition triggered nanoparticle anchored gelation" (or PTTNAG) of the hydrogel. Human mesenchymal stem cells (MSCs), have been incorporated into the gel by i) placing them on the assembled gel surface - the cells responded by migrating and proliferating throughout the matrix of the gel, and more interestingly, ii) combining the MSCs with the PCPH in the liquid phase and allowing PTTNAG of the polymer matrix to occur around the cells. In both cases, cell viability was excellent throughout a series of 14-28 day experiments. The work was expanded by the exploration of PTTNAG temperature tailorability. This was achieved with the incorporation of the relatively polar comonomer dimethylacrylamide (DMAc), and non-polar comonomer glycedyl methacrylate (GMAc) which respectively increased and decreased the PTTNAG and lower-critical solution temperature (LCST) of the resulting gels. Crucially, it was found that the PTTNAG temperature can be tailored precisely and incorporation of DMAc did not affect cell viability. The process also opened several novel avenues for gel processing possibilities, including facile casting, extruding and electrospinning. Well defined and uniform electrospun fibres with diameters ~300nm are presented. The production of continuous, uniform flat PNIPAM/ clay sheets of 300pm -1000pm achieved using an industrial film extrusion line is detailed. This work represents an innovation in the way in which such hydrogels can be manufactured and produced safely and cleanly, with no additives, no energy input and no toxic by- products. Interactions between polymer and water are examined by monitoring the dehydration of 3 separate hydrogel formulations using ATR-FTIR. The pseudo diffusion coefficient (in this instance, the diffusion of water out of the polymer matrix) was not affected by dopant composition, but instead, the intercept of the slope was altered markedly. Cross-link type, cross-link density, initiation method and addition of dopants have a strong influence on the swelling/ deswelling behaviour of the hydrogels under study. PNIPAM/ clay gels exhibit much larger volume changes than those prepared with chemical cross-linking agent methylenebisacrylamide (BIS). Deswelling magnitude increases with decreasing cross-linker content for all gel types examined. Thermal deswelling is hindered in dopant-incorporated networks. The aqueous dilution of the nanocomposite in the liquid phase affects gel deswelling behaviour when clay concentration is.low. De/reswelling of PNIPAM/ clay, PNIPAM/ BIS and gelatine-doped PNIPAM/ clay gels can be induced by adjusting the alcohol volume fraction of the media. BIS cross-linked gels exert restricted swelling/ deswelling behaviours compared to those cross-linked with clay. Cross-link density within systems does not have a significant impact on cononsolvency behaviour, although the incorporation of gelatine imposes some restriction on it, directly relative to gelatine concentration. X-ray diffraction (XRD) data proved the exfoliation of clay in the nanocomposite system post- PTTNAG. DMA data revealed that the viscoelasticity of the gels can be tailored with varying the nature and quantity of dopant materials. Gels doped with hyaluronic acid (HA) most closely resemble the mechanical properties of bovine NP tissue. IV Table of Contents Declaration II Acknowledgements III Abstract IV Table of Contents V List of Abbreviations XIII Chapter 1 - Introduction 2 1.1 Polymers