Oxidation Degradation And Biotribological Properties Of UHMWPE

Ultra-high molecular weight polyethylene(UHMWPE) has excellentbiocompatibility, chemical stability, impact resistance, wear resistance and corrosionresistance, and it is more desirable to the medical polymer materials and is widelyused in artificial joint replacement operation. During the long-term applicationprocess of UHMWPE artificial joint, body fluid plays the role of lubrication and alsoplays the role of degradation and corrosion. Body fluid causes oxidation, wear andwear debris accumulation easily leads to osteolysis and aseptic loosening, which increase the suffering of patients, and limit the longevity of artificial joints.In this paper, pharmaceutical grade UHMWPE powder and natural vitamin Ewere used as raw materials to prepare UHMWPE and UHMWPE/VEsamples bythermal compression molding method, and then they are soaked in simulated bodyfluid. Then, the oxidative degradation mechanism of UHMWPE and UHMWPE/VEwas studied.The UHMWPE sample cooling in air has a higher degree of crystallinity thanthat of rapid cooling method due to its slow cooling rate in thermal compressionmolding. The UHMWPE sample cooling in air has higher ball indentation hardness,yield strength, tensile strength, creep resistance and biotribological properties thanthat of cooling in water or liquid nitrogen, but its elongation and wettabilitydecreased.Large amounts of oxygen functional groups are formed on the surface ofUHMWPE sample when it is soaked in simulated body fluid for five years and thisincreases the oxygen content of UHMWPE sample surface. Wettability of UHMWPEsample surface becomes better and its crystallinity increases, the mechanical andbiotribological properties are reduced when soaked in simulated body fluid for fiveyears. The main wear mechanisms of UHMWPE are scratches, furrows and fatiguespalls. Anti fatigue performance of UHMWPE is worse when it is soaked in simulatedbody fluid for longer time and there are more spalls.Crystallinity of UHMWPE sample is improved and oxygen content is decreasedwhen added vitamin E in thermal compression molding. The mechanical andbiotribological properties of UHMWPE increase and surface wettability decreasesslightly when vitamin E was added in.Oxygen content of UHMWPE and UHMWPE/VEsample surface is increased when soaked in simulated body fluid for one year and this increased the wettabilityand crystallinity and reduces the mechanical and biotribological properties ofUHMWPE and UHMWPE/VEsample. The addition of vitamin E alleviates theoxidative degradation rate of UHMWPE sample and hinderes the increase ofcrystallinity and the decrease of biotribology. The mechanical properties which reflectthe overall performance of UHMWPE change a little, because the soaking time isshort.Oxygen content of UHMWPE and UHMWPE/VEsample surface is reduced andcrystallinity was increased when cycle2500000in simulated body fluid. There isfriction and wear when force acting on the surface of UHMWPE and UHMWPE/VEsample and formes a large number of furrows, this increases the mechanical andbiotribological properties of UHMWPE and UHMWPE/VEsample.Crystallinity and oxygen content of UHMWPE increase when used in vivo fortwo and a half years and this leads to the decrease of mechanical and biotribologicalproperties. Wettability of UHMWPE becomes better mainly due to the changes ofsurface atoms and atomic clusters.Free radicals will be formed when UHMWPE is molded, soaked in simulatedbody fluid and used in vivo. These free radicals can react with oxygen to form peroxyradicals. Peroxy radicals can absorb hydrogen atoms from the UHMWPE molecularchain nearby and hydrogen peroxide and free radicals are generated. New free radicalsparticipate in the formation of a series of new groups and reaction with oxygen andthen accelerate the oxidation of UHMWPE.Oxidative degradation products of UHMWPE include ketones, alcohols, estersand acids when it was soaked in simulated body fluid or used in vivo. The formationof ketone and ester reaction will not accelerate the degradation of UHMWPE, but theformation of alcohol and acid reaction will accelerate the oxidation of UHMWPEbecause there generates free radicals when alcohol or acid produce. The product ofacids and esters will be limited because there is low oxygen content in simulated bodyfluid and the main products of UHMWPE oxidation are ketone and alcohol. Oxidativedegradation rate of UHMWPE will be accelerated when used in vivo, because it wassuffers complex stress in the work process.Chroman in the molecular structure of vitamin E can absorb and stabilize peroxyand alkyl radical, forming phenoxy radical. Phenoxy radicals can react with alkyl ofitself and become more stable and then prevents the degradation of UHMWPE.