Development and tribological characterization of polyvinyl alcohol-based artificial cartilage for in vitro testing of viscosupplementation gels

Introduction: Viscosupplementation is a treatment commonly used to restore joint lubrication in moderate osteoarthritis, although the effect of different intra-articular lubricants in friction reduction remains to be fully understood and tested in vitro. The aim of this study was to develop an artificial cartilage that mimicked the mechanical and tribological behavior of human articular cartilage, enabling in vitro evaluation of novel hyaluronic acid (HA)-based gels for viscosupplementation. Methods: Poly (vinyl alcohol) (PVA) hydrogels were evaluated by comparing different polymer concentrations (15%, 20%, and 25%) in water to identify which most closely replicates the compressive and frictional behavior of native articular cartilage. Results and discussion: Scanning electron microscopy showed that higher polymer concentrations reduce pore size and increase surface irregularities, reflecting a denser network. Compressive testing indicated that the hydrogel stiffness rises progressively with polymer concentration, yielding compressive moduli within the physiological range of human cartilage. Tribological tests, performed using phosphate-buffered saline (PBS) as a lubricant under relevant loads and motion frequencies, revealed that friction also increases with polymer content. Among the tested concentration, 20% PVA hydrogel offers the most favorable combination of stiffness and lubricity, with a compressive modulus of approximately 300 kPa and a friction coefficient of about 0.14. Additional tests were performed by using four different HA-based viscosupplementation gels as lubricants. In all cases, a pronounced reduction in friction was observed, with coefficients decreasing to values between 0.02 and 0.06. In addition, microscopic surface analysis after testing showed a reduction in surface wear, confirming the protective and lubricating effect of HA-based gels. Overall, these findings indicated that PVA hydrogels, particularly at 20% concentration, can effectively be adopted as a reproducible and physiologically relevant equivalent of articular cartilage.