The development of protein-functionalised plasma polymer biointerfaces for orthopaedic applications

Abstract

Orthopaedic implants are an ever-growing global industry with hundreds of thousands of operations performed annually. Titanium is the standard material for load-bearing orthopaedics because of the biocompatibility and favourable mechanical properties. Despite a variety of surgical strategies, a significant number of implants experience post-operative complications or long-term implant loosening. Biomolecule functionalisation is a promising approach to create a biologically-active surface that reduces the potential for adverse post-operative complications and encourages bone formation. The biomolecules commonly utilised for enhancing bone formation either increase cell recruitment or accelerate mineralisation. An ideally functionalised surface would simultaneously enhance both. Biomolecule-functionalisation of Ti surfaces is performed through physical adsorption, chemical linker molecules, or plasma-based technologies that require subsequent chemical processing. Few techniques have provided a simple, reproducible, and scalable approach to transition from the laboratory into industry, and no approach that easily enables permanent immobilisation of multiple biomolecules to a surface. This thesis explores the application of radical-functionalised plasma polymers films (rPPFs) as multifunctional protein biointerfaces for orthopaedics. rPPFs are plasma deposited coatings that covalently bond biomolecules through embedded unpaired electrons. The mechanical and biological properties of rPPF coatings were optimised for titanium substrates, and the effects of the radical fluxes on surface chemistry and cell behaviour were investigated. Two multifunctional protein surfaces were developed and comparatively examined against the component proteins for bone formation potential with primary osteoblasts and mesenchymal stem cells. Overall, this work shows the versatility of rPPFs and opens a potential avenue for translating biomolecule-multifunctionalisation into industry settings.