Analysis of variables influencing the accelerated ageing behaviour of ultra-high molecular weight polyethylene (UHMWPE)

Ultra-high molecular weight polyethylene (UHMWPE), used in total joint replacements, undergoes oxidative degradation following gamma irradiation sterilisation. Methodologies are therefore required which can rapidly evaluate any newly developed material, processing or sterilisation technology. This study has investigated methodologies for the accelerated ageing of gamma irradiated UHMWPE that will simulate 3 or 5 years shelf ageing. These have been based around American Society for Testing and Materials Standard F2003-00, method B (70°C in 5 bar pressurised oxygen for 14 days). Within the scope of this study explanations for the unacceptably high level of interlaboratory uncertainty have been proposed. Variables within the accelerated ageing methodology which have been found to influence the level of oxidative degradation include temperature, heating rate, humidity, machining of specimens and time interval between gamma irradiation and accelerated ageing. The influence of these factors has been explored using a Taguchi analysis of variables.