Ultra High Molecular Weight Polyethylene (UHMWPE) for Orthopaedic Devices: Structure/Property Relationships

The following chapter details the structure property relationships in medical-grade polyethylene materials. The chapter is divided into the following sections: The first section is an introductory section on comparing medical grade polyethylenes with more conventional high density grades, and the second section deals with chain structure and alignments. The third section is devoted to describing crystallinity and melting behaviour using classical Avrami and Lauritzen - Hoffman theory. This is expanded to crystal growth regimes. The fourth and fifth sections are dedicated to molecular weight and mechanical performance with particular focus on creep behaviour as this is particularly pertinent for medical device materials. The final section describes radiation induced changes in the microstructure of polyethylene as a result of gamma sterilisation processes. These changes have been linked to wear rates and importantly wear debris has been implicated in joint loosening mechanisms. Latest research on heat treated "stabilised" polyethylenes is discussed and this is expected to influence medical device performance in vivo.