Microwear phenomena of ultrahigh molecular weight polyethylene cups and debris morphology related to gamma radiation dose in simulator study.

Ultrahigh molecular weight polyethylene (PE) cups with 0, 2.5, 50, 100, and 150 Mrad radiation treatments were run in a hip simulator for comparison of the microwear phenomena on the cup surfaces with the corresponding debris morphology. In general, the size and frequency of the PE surface fibrils and the size of the retrieved PE debris decreased with increasing radiation dose. The fibril size and shape on the cup surfaces were well correlated with the radiation dose. The fibrillar shape and size were found to be proportional to the square root of the radiation dose. However, the trend for size and shape factors of the wear debris related to the radiation dose was weak at best. Thus, the morphology of the PE fibrils on the cup surfaces was more sensitive to variations in the radiation dose than the actual wear debris. The wear response appeared to be a three-step process, which was dependent on the formation of surface nodules or ripples, the teasing out of surface fibrils, and the toughness of the PE matrix in releasing a wear fibril to form a debris particle. The tougher PE became with increasing radiation dose, the harder it was for the PE fibrils to break out into wear particles.