Design And Tribological Properties Of UHMWPE Surface Bionic Articular Cartilage

Ultra high molecular weight polyethylene(simplified as UHMWPE)is the most widely primary bearing material in artificial joint applications for over fifty years.More than 70%of the total artificial joint are composed of metal or ceramic femoral head and UHMWPE acetabular cup.However,the wear particles are produced by the worn of UHMWPE,which will be phagocytosed by the macrophages and a large number of bone-resorptive factors are released.Consequently,this leads to the aseptic loosening and eventual failure of artificial joints.Therefore,it is important to improve the tribological properties of UHMWPE to prolong the natural life of artificial joints.The Natural articular cartilage(AC)system is a special kind of tissue that is the porous collagenous network filled with interstitial fluid and the brush-like layer formed with proteoglycans and hyuronic acid(HA).These provide the extreme boundary lubrication and extraordinarily low friction(about 0.0005?0.04),with the average serive life of 70 years.It is important to investigate the multiple lubrication mechanisms of proteoglycans polymer brushes and porous structure in AC,which has important theoretical and practical applications for preparing the artificial joints and extending the life.In this study,we created the antifriction wear resisting bionic artificial joint materials by mimicking the polymer brushes and porous structure of AC.The UHMWPE was used as the base material.We mimicked the proteoglycans polymer brushes in AC first.The polymer brushes were grafted on the surface of UHMWPE powder with the method of ultraviolet(UV)irradiation grafting,and then the powders were hot pressed to form the bulk artificial joint with "sustainable" antifriction wear-resisting polymer brushes.The tribological properties,mechanical properties and microstructure were investigated.The MPDSAH polymer brushes with long molecular chains and charges,and the AM neutral polymer brushes with short chains and no charges,were used to prepare the artificial joint respectively.The performance and lubrication mechanism were compared and analyzed.Then the gamma irradiation crosslinking was used to modify the UHMWPE with polymer brushes structure.The microstructure,tribological properties and mechanical properties were investigated to determine the effects of irradiation crosslinking.Finally,based on the research of polymer brushes,mimicking the porous,polymer brushes structure and lubrication mechanisms of AC,an AC(articular cartilage)-like bionic material was designed via two steps:employing the sodium chloride leaching techniques to form a interconnected porous UHMWPE,and followed by the modification of MPC(2-methacryloyloxyethyl phosphorylcholine)with UV grafting.The bionic articular cartilage gradient materials have the porous and polymer brushes structure,and the multiple lubrication mechanisms were investigated.The friction coefficient and wear rate of grafted UHMWPE bionic artificial joint decreased.The wear resistance of UHMWPE with "sustainable" antifriction wear-resisting polymer brushes has been improved significantly under the long term test.The failure of polymer brushes in a short time was solved.The crystallinity,elasticity modulus,yield strength,breaking strength and ultimate strain decreased.The tribological properties of charged MPDSAH polymer brushes were superior to neutral AM polymer brushes,however,the mechanical properties of modified UHMWPE with short chains AM polymer brushes was better than that of modified UHMWPE with long chains MPDSAH polymer brushes.Gamma irradiation crosslinking improved the tribological properties of UHMWPE.However,the tribological properties of irradiation crosslinking UHMWPE-g-AM have not been improved.The friction coefficient and wear rate are higher than that of UHMWPE-g-AM without irradiation crosslinking.Compared with irradiation crosslinking,the grafted polymer brushes could effectively improve the tribological performance.After irradiation crosslinking,the toughness fracture is still the main fracture mechanisms.The wettability of bionic articular cartilage gradient materials with porous and polymer brush structure was improved and the conact angle was 0° with the increase of time.The friction coefficient decreased,which was lower than that of UHMWPE and porous UHMWPE.The lubricating properties have been efficiently improved through the hydrodynamic lubrication of porous UHMWPE structure and boundary lubrication by polymer brushes.The research will provide the foundation application,not only for total joint replacements but also as a platform technology in other biomedical contexts,in which lubrication plays a role.