Accelerated aqueous aging simulation of in vivo oxidation for gamma-sterilized UHMWPE

In vivo oxidation of gamma air-sterilized ultrahigh-molecular-weight polyethylene (UHMWPE) has been observed when joint replacement hip and knee components are explanted during revision surgery. The purpose of the present study was to extend a previously published accelerated aging protocol for gamma-sterilized UHMWPE. Unsterilized and gamma-sterilized GUR 1150 resin samples were aged in phosphate-buffered saline (PBS) at 40 or 50 degrees C for up to 52 weeks. Under these conditions, slower changes in oxidation index (OI) occurred than those previously observed by aging at 60 degrees C. Reduction of aging temperature below 60 degrees C also changed the kinetics of oxidation such that the aldehyde peak (1732 cm(-1)) present at higher temperature was eliminated making the ketone/carboxylic acid region (1713-1718 cm(-1)) the primary region contributing to the calculation of the OIs for each group. The oxidation profiles obtained after 52 weeks at 40 and 50 degrees C were consistent with retrievals that have undergone low oxidation, associated with maximum OI values of less than 1. Aging at 50 degrees C represents a compromise between the slower oxidation rate of in vivo temperatures and the nonphysiological kinetics of elevated temperatures in an aqueous environment. However, even at 50 degrees C over a year of in vitro aqueous aging will be necessary to reproduce the oxidation levels observed in long-term implanted acetabular retrievals. (