The Structure And Property Induced Byγ-ray Irradiation Crosslinking Of The Ultra-High-Molecular-Weight Polyethylene Used In Joint Arthroplasty

The wear of Ultra-High-Molecular-Weight Polyethylene (UHMWPE) is thecritical factor that limited the lifetime of artificial joint arthroplasty. The cross-linkingmodification for improving wear resistance changes the polymer structure, whichdirectly affects the mechanical properties and oxidation stability of the material. Inthis paper, UHMWPE was irradiated by γ-ray with four different irradiation doses(50kGy,75kGy,100kGy,200kGy) respectively, and then was post-irradiationheat-treated. The effects of irradiation and heat treatment on the structure, mechanicalproperties and oxidation stability of UHMWPE are investigated as well.According to ASTM F2565-2006specified standard test methods, the effects ofirradiation dose on molecular structure such as crystallinity, crosslinking degree andmechanical properties such as tensile properties, compression modulus, impactstrength and small punch are investigated with DSC, FTIR, in situ laser micrometer,electronic material testing machine and impact material machine. The effect ofirradiation doses on oxidation extent of the irradiation crosslinked UHMWPE whichwas accelerating aged is researched with oxygen bomb and FTIR as well. In addition,the irradiation crosslinked UHMWPE which was irradiated with specific irradiationdose was heat-treated, and then the effects of different heat treatments on thecrystallization behavior, mechanical properties and oxidation stability of highlycrosslinked UHMWPE are discussed.It is showed that the crystallinities of crosslinked UHMWPE of which wasirradiated with four doses (50kGy,75kGy,100kGy,200kGy)increased by6.4%,12.2%,16.3%and22.9%respectively; Meanwhile crosslinking density, bulkdensity, trans-vinylene index all increased monotonically as irradiation doseincreased. Besides that, all the parameters above except the trans-vinylene indexreached saturation after about100kGy irradiation. In the lower dose range from50kGy to100kGy, tensile strength increased slightly, elongation decreased by1%to10%, compression modulus increased by20%to49%, and impact strength decreasedby9.5%to23.5%. When irradiation dose reached200kGy, elongation decreased by28.5%sharply. In addition, small punch test results indicate that the material strength,ductility and toughness can be balanced with the irradiation dose of75kGy.Accelerated aging tests demonstrated that oxidation index increased monotonically with irradiation dose, the index increased significantly to615%of the non-irradiatiedsample with irradiation dose exceed100kGy. In addition, oxidation indexes ofcrosslinked UHMWPE can be reduced by post-irradiation heat treatment such asannealing and remelting. Remelting process deceased crystallinity, strength andstiffness of the material, and meanwhile maintained ductility and toughness, andoxidation index was the lowest; anneal process can maintain mechanical properties. Inconclusion, irradiation dose range from50kGy to100kGy, and the heat treatment forthe irradiation crosslinked UHMWPE can greatly contribute to optimizecomprehensive properties of UHMWPE.