Coupling mechanism of bioinspired artificial composite synovial fluid on the tribological behavior of artificial joints

Changes in the components of synovial fluid in the human body have an important influence on the tribological behavior of artificial joints. Based on the concentration of components in the synovial fluid after arthroplasty, “hard−soft” joint pair materials composed of cobalt‒chrome‒molybdenum (CoCrMo) and highly crosslinked polyethylene (XLPE) were used as the research objects. Composite synovial fluid containing different concentrations of albumin (Alb), γ-globulin (γ-Glo), hyaluronic acid (HA), and phospholipids (PLs) was prepared. By studying the influence mechanism of single component concentration changes on the tribological properties of joint pair materials, the friction and wear behavior of joint pair materials in different composite synovial fluids are systematically explored. The coupling mechanism among the components is clarified, and the wear mechanism of the joint pair materials under different composite synovial fluids is revealed. In addition, the results of 2 million in vitro simulated wear experiments of CoCrMo‒XLPE artificial joints in composite synovial fluid were further studied. Furthermore, this study validated the influence of the concentration of the composite synovial fluid on the friction and wear properties of artificial joints under actual working conditions. The results show that the four main components in the composite synovial fluid have a great influence on the friction and wear properties of the “hard–soft” joint pair materials. When the concentration of PL increased from 0 to 0.45 mg/mL, the wear rate decreased by 69.6%, and the coefficient of friction (COF) decreased by 63.3%. The coupling mechanism between PLs, HA, and proteins significantly affects the adsorption of the membrane and affects the tribological behavior of the artificial joint. In addition, the simulated wear results of artificial joints in composite synovial fluid are consistent with those of friction and wear testers. The concentration of each component in the composite synovial fluid significantly affects the lubrication of the artificial joint, and the degree of influence becomes more obvious during long-term service. In summary, this study provides a theoretical basis for the study of composite synovial fluid and the improvement of the lubrication performance of artificial joints and is highly important for prolonging the service life of artificial joints.