Oxidation behaviour in prosthetic UHMWPE components sterilised with high energy radiation in a low-oxygen environment

Oxidation of the UHMWPE component during sterilisation with high energy radiation has been recognised as one of the main problems affecting the durability of orthopaedic implants. Oxidation is always present in radiation-sterilised polymeric components due to the oxygen diffused into UHMWPE. Hydroperoxides are the first products of the oxidation cycle and they are also a convenient species to follow for monitoring the oxidation. In the present study, the early stages of oxidation were investigated by assessing the hydroperoxide levels and distribution in a selection of ready-to-use UHMWPE prosthetic components. The samples included in the study were chosen from a larger group, according to the following criteria: they were packaged in a low-oxygen environment, radiation-sterilised and carbonyl free. FTIR spectroscopy and derivatisation techniques were used to characterize the hydroperoxide concentration and distribution. Hydroperoxides were detected in all samples, despite the sterilisation in inert atmosphere. Three different behaviours were identified and discussed and a correlation with the packaging and sterilisation conditions is proposed.