Effect of radiation on the microstructure and mechanical property of ultrahigh molecular weight polyethylene used in orthopedic prostheses

The effect of radiation on the microstructure and mechanical property of ultra high molecular weight ployethylene (UHMWPE) used in orthopedic implants was investigated. The raw material used in this study was GUR 4150 ram extruded UHMWPE bar. The UHMWPE specimen was irradiated at 140□ in oil and room temperature under nitrogen with different dosages of an electron beam (EB) for the purposes of enhancing the crosslinking extent of the polymer. Following irradiation at room temperature, the UHMWPE specimens were thermally treated at various temperature to eliminate all the remaining free radicals. Surface oxidation of the UHMWPE samples according to the irradiation and thermal treating conditions were verified by FTIR-ATR. An electron spin resonance (ESR) spectroscopic study was Undertaken to investigate the remaining radicals in UHMWPE. The crystalline structure and mechanical properties of the irradiated UHMWPE were compared after the crosslinking of the EB. The crystalline structure and degree of crystallinity of irradiated UHMWPE were investigated using DSC, SAXS and WAXD. Mechanical properties such as the tensile strength were measured. The polymer pin on a metal plate type testing apparatus was used to test the wear property. The melt-irradiated samples had a higher crosslinking extent compared with the room temperature-irradiated and the UHMWPE control. The crystallinity and lamellar thickness of UHMWPE irradiated at room temperature increased much more comparing with specimens irradiated at 140□. The melt-irradiated UHMWPE had a better wear resistance than the room temperature-irradiated and the UHMWPE control