On the Bio-functionalisation of Polyether Ether Ketone using Plasma Immersion Ion Implantation

Abstract

Orthopaedic implantable devices face significant challenges to their long term stability and integration. One important reason for implant failure is mechanical incompatibility with surrounding tissues, leading to aseptic loosening. Polyether ether ketone (PEEK) is a promising candidate for the bulk material in orthopaedic devices due to its outstanding chemical stability and bone-like mechanical properties. Unfortunately, due to its chemical stability, PEEK is bioinert and does not interact favourably with cells and proteins. Plasma immersion ion implantation is used in this thesis to modify a surface layer of PEEK for improved bioactivity. This thesis explores the radical generation; subsequent chemical and mechanical modification; and reports cell culture studies that measure the attachment, proliferation, gene expression and rate of bone apposition on the surface. Radicals generated by PIII treatment in a sub-surface layer of a polymer can diffuse through the ion implanted region and are accurately modelled by Fick's second law of diffusion with temperature activation. The diffusion constant and activation energy allow for long lived radicals in the sub-surface layer, that react to form covalent bonds with proximate species once on the surface. Radicals at the surface react with atmospheric oxygen when aged in air, generating a more polar, hydrophilic surface that is permanent. Radical mediated cross-linking results in surface hardening with increasing treatment time, indicating that the mechanical properties can be tuned for specific biological sites and applications. Radicals emerging at the surface are capable of covalently immobilising biomolecules when incubated in solution. PIII treated PEEK surfaces decorated with tropoelastin display significantly more bioactive properties during cell culture, resulting in markedly improved bone deposition and morphology. This work presents a viable alternative to traditional metallic orthopaedic implants and provides a solid foundation for translational research and development of PEEK based iso-elastic orthopaedic devices.