Carbon reinforced UHMWPE composites for orthopaedic applications : characterization and biological response to wear particles

Abstract: Joint replacements have considerably improved the quality of life of patients with joints damaged by disease or trauma. However, problems associated with wear particles generated due to the relative motion between the components of the bearing are still present and can lead to the eventual failure of the implant. Ultra high molecular weight polyethylene (UHMWPE) has been extensively used as a bearing surface in total joint replacements. Although in the short- to medium term UHMWPE provides excellent clinical performance, in the longer term, problems associated with its high wear characteristics and biological responses to polyethylene wear particles leads to the failure of the implants.The first part of the thesis focuses on the current status of total joint replacements (hard-on-soft and hard-on-hard bearings), with particular attention on implant wear debris and the biological response to wear debris, as well as on the tribological behaviour of the potential materials currently under investigation. The aim of the second part of the thesis consists of an analysis of the wear rate and the size and volume distributions, morphology and biocompatibility of the wear debris generated from a multiwalled carbon nanotube (MWCNT) reinforced polyethylene material compared with conventional UHMWPE. The results showed that MWCNT’s can improve the characteristics of UHMWPE, in terms of both wear rate and biocompatibility. UHMWPE-MWCNT composite material was shown to generate low wear rates and a reduced osteolytic and cytotoxic potential compared to conventional virgin polyethylene of the same grade.The final part of the thesis focuses on the possibilities of graphene oxide (GO) as reinforcement of UHMWPE. The aim of this work is to investigate the manufacturing procedure to prepare a homogeneous UHMWPE/GO composite under optimised conditions that might improve the performance of UHMWPE in artificial joints. In this study, composites prepared under different mixing conditions were thermally and morphologically characterised and compared with conventional UHMWPE. The results showed that, under optimized manufacturing conditions, GO has the ability to improve the performance of conventional UHMWPE. This thesis has provided an insight into the potential of carbon based composites as an alternative to conventional UHMWPE for use in total joint replacements and further work concerning the influence of graphene oxide on the tribological performance of UHMWPE/GO composites is currently under investigation.