Anti-Oxidation Treatment Of Uhmwpe And Its Biotribological Behavior

Ultra-high molecular weight polyethylene (UHMWPE) has excellent biocompatibility, chemical stability, impact resistance, wear resistance and corrosion resistance, and it is more desirable to the medical polymer materials. However, during the long-term application process, oxidation, wear and wear debris accumulation easily lead to osteolysis and aseptic loosening, which increase the suffering of patients, and limit the longevity of artificial joints. In this paper, medicine class UHMWPE powder and natural vitamin E were used as raw materials to prepare UHMWPE/VE composites by thermal compression molding method, and then they were irradiation crosslinked byγ-ray. Eventually, anti-oxidation and wear-resistant irradiation crosslinked UHMWPE/VE was made as a new type of artificial joint materials.Conventional atmosphere molding method will lead to the formation of residual internal porosity defects inside UHMWPE, which resulting in a decrease of its mechanical properties and biotribological properties; while low-vacuum environment molding method can effectively eliminate the internal porosity defects inside UHMWPE, and increase its mechanical properties and biotribological properties.Irradiation crosslinking could improve the comprehensive mechanical properties and the abrasive wear resistant properties of UHMWPE, but the increase in degree of crosslinking will reduce its plastic. VE doping can effectively reduce the oxidation of UHMWE in the process of irradiation crosslinking, improving its fatigue performance. However, high concentrations of VE doping will reduce the crosslinking degree of radiation crosslinked UHMWPE, which will reduce the mechanical properties and biotribological properties.Irradiation crosslinking results in the formation of a large number of residual free radicals existing inside the UHMWPE, which will react with oxygen. As a result, the extent of oxidation degradation is very serious during accelerated aging process. After accelerated aging, the mechanical properties and biotribological properties of irradiation crosslinked UHMWPE reduces significantly, while the VE doping can significantly enhance the anti-oxidation stability of irradiation crosslinked UHMWPE, and the change of its mechanical properties and biotribological properties is not obvious.The crystal structure of the surface of compression molded UHMWPE parallel to the surface of the specimen. Irradiation crosslinking improves the crystallinity of UHMWPE, increases the density of its crystal structure. After accelerated aging, there have been a large amount of fracture phenomena of crystal structure on the surface of irradiation crosslinked UHMWPE sample; while the crystal structure on the surface of irradiation crosslinked UHMWPE/VE sample has not changed significantly.The surface is the site which is affected by environmental factors most directly, and also in direct contact with oxygen in the air. After accelerated aging, the hardness and elastic modules of the surface of UHMWPE specimen increased, while the bulk hardness and bulk modulus of elasticity reduced.Irradiation crosslinking increases the anti-creep properties of UHMWPE, reduces its sensitivity to load response. Accelerated aging will lower the anti-creep properties of irradiation crosslinked UHMWPE; while the performance of irradiation crosslinked UHMWPE/VE has not changed obviously after accelerated aging.Irradiation crosslinking increases the surface free energy and enhances the wettability of UHMWPE, and a small amount of VE doping does not change its surface free energy and wettability. Water absorption of UHMWPE is very low, irradiation crosslinking and VE doping would further reduce its water absorption. After immersed in simulated body fluid for six months, VE content in irradiation crosslinked UHMWPE/VE does not show a significant change.Hip simulation test results indicate that the wear performance of irradiation crosslinked UHMWPE/VE improves significantly. Furthermore, irradiation crosslinked UHMWPE/VE could effectively control the size of wear debris, decrease the number of wear debris, as well as the extent of adverse reactions of cell caused by wear debris, and finally improve the reliability and stability of artificial joints.