Effect of coupling between pH and composite synovial fluid components on tribological behavior of PEEK-XLPE hip joint materials

The tribological performance of hip joint materials in the synovial fluid is substantially influenced by environmental factors. In this study, the tribological properties of polyether-ether-ketone (PEEK)-highly crosslinked polyethylene (XLPE) hip joint materials were investigated in composite synovial fluids with varying pH conditions, revealing the coupling mechanism between pH and composite synovial fluid components. The lubrication efficacy of the composite synovial fluid under physiological conditions was validated through a 2 million-cycle hip joint simulation test. Results indicated that the coefficient of friction (COF) decreased with the increasing pH, while the wear factor remained stable at pH = 7.5 and pH = 8.0 but decreased progressively at pH = 8.5. Notably, the Fluid C demonstrated significant pH sensitivity, reducing the wear factor by 89.12 % when pH increased from 8.0 to 8.5. Moreover, the results of the hip joint simulation tests were consistent with the sliding tribology tests. The component concentration regulated the lubrication efficiency, with amplified effects during long-term service. Hence, this study elucidated wear mechanisms in “soft-soft” hip joint materials under simulated physiological conditions and provided critical insights for predicting the lifespan of polymer-based artificial joints.