Abstract
UHMWPE crosslinked using Gamma radiation is believed to have improved wear properties, and this has been extensively studied during the past 10 years. Mechanical properties, oxidation, and wear properties of UHMWPE materials subjected to various thermal treatments have been investigated immediately after irradiation as well as after several years of aging. Nevertheless, the relationship between all these parameters is not yet fully understood. The aim of this study was to investigate the relationship between the thermal treatments that could be applied to irradiated UHMWPE [lower (ฮณ60) or higher (ฮณ150) than 140ยฐC, the melting temperature of the polymer] and the mechanical properties, the oxidation and the fracture behavior of the material. The effect of artificial aging on these properties was also investigated. This study concludes that immediately after the annealing, the mechanical properties (UTS and ฯต) of the irradiated and annealed material are improved compared with those of nonirradiated material. Although nonirradiated material has higher fracture toughness than irradiated and annealed materials, the materials break according to the same mechanism of fracture. After aging, no changes could be observed in any of the measured properties for nonirradiated material. On the other hand, important changes could be seen in both irradiated and annealed material after aging. Both UTS and ฯต decreased, much more so in the case of ฮณ60. Furthermore, the aging induced a subsurface peak of oxidation in both irradiated and annealed materials, twice as intense for ฮณ60 than for ฮณ150. The mechanism of fracture of these materials changed drastically after aging, probably due to the presence of the oxidation peak, which seems to occur at a location where cracks initiate easily compared with the nonoxidized bulk of the material. In the case of ฮณ60, it seems clear that a correlation between mechanical property, oxidation, and fracture mechanism exists. Such a relationship could not be found for ฮณ150. ยฉ 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 908โ917, 2003