Impact of Dose-Rate on Rheology,Structure and Wear of Irradiated UHMWPE

Ultrahigh molecular weight polyethylene (UHMWPE) is used as a bearing material in total joint replacements (TJR). UHMWPE for TJR is usually modified by irradiation and thermal treatment to increase wear resistance. We modified UHMWPE in three ways, differing in radiation dose-rate and/or atmosphere during irradiation. Rheological properties before and after irradiation were determined by means of oscillatory shear measurements. Structural changes were followed by X-ray diffraction, infrared spectroscopy, electron spin resonance, and solubility measurements. Wear resistance of selected samples was obtained by the pin-on-disk method. Rheological properties changed sensitively with modification conditions including radiation dose rate. Moreover, rheological results correlated well with both crosslinking extent and wear resistance. Finally, it was demonstrated that the optimal radiation dose, i.e. the dose leading to maximum crosslinking density and wear resistance, was different for each of the three modification procedures.