Coupling influence between environmental factors and synovial fluid components on tribological behavior of hip joint materials

Environmental factors greatly affect the tribological behavior of hip joint materials in synovial fluid. In this paper, four groups of the synovial fluid with different concentrations of albumin (Alb), γ-globulin (γ-Glo), hyaluronic acid (HA), and phospholipids (PLs) were prepared based on the concentration of each component of the synovial fluid after artificial joint replacement. Then, taking cobalt-chrome-molybdenum (CoCrMo) and high crosslinked polyethylene (XLPE) as research objects of the hip joint materials, the tribological behaviors in the synovial fluid with different pH values and temperature were systematically explored, elucidating the influence mechanisms of external conditions and synovial fluid components on friction and wear behaviors. Results indicated that the tribological behaviors of hip joint materials were significantly affected by the pH value and temperature of the synovial fluid. The coefficient of friction (COF) of the hip joint materials in the synovial fluid initially decreased and then increased with the pH value, reaching a minimum at pH= 8.0, and sample 4 was the most sensitive to pH change. The COF of the hip joint materials in the synovial fluid ascended with temperature, showing an opposite trend to calf serum (protein concentration of 30 mg/mL) in the standard experiment. In addition, the wear of the hip joint materials was more severe in the synovial fluid with lower pH (pH=7.5 and pH=8.0) and mild in the synovial fluid with higher pH (pH=8.5). Additionally, the wear of the hip joint materials in the synovial fluid and calf serum in the standard experiment increased with the ascend of temperature, and the wear in calf serum in the standard experiment was the most affected by temperature. In conclusion, this study sheds light on the tribological behaviors and mechanisms of artificial hip joints under simulated working conditions, providing a crucial foundation for accurately evaluating the bio-tribological characteristics of artificial joint materials.