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

Abstract

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.

Keywords:

• joint replacement
• radiation dose rate
• rheology
• UHMWPE
• wear resistance

Acknowledgements

This work was supported through grants GACR 106/04/1118 (Grant Agency of the Czech Republic) and MSMT 2B06096 (Ministry of Education, Youth and Sports of the Czech Republic). The authors thank Dr. P. Bartoníček and his team from the Institute of Nuclear Research, Řež, for irradiation of samples and valuable consultations.