The impact of superficial zone damage on the tribological performance of cartilage: Implications for early intervention in osteoarthritis

The superficial zone of the articular cartilage plays a vital role in maintaining low friction and wear within joints because of its excellent lubricating properties. While the tribological properties of cartilage with an intact superficial zone have been widely studied, it remains unclear how different degrees of superficial zone damage affect cartilage lubrication, friction, and wear. In this study, we conducted friction and wear experiments to assess changes in cartilage performance before and after damage and examined surface roughness and microstructure to understand lubrication and wear mechanisms. We also used finite element method (FEM) simulations to study the evolution of wear behavior in damaged cartilage. Research has shown that as damage to the superficial zone of cartilage worsens, its lubrication performance continuously decreases, leading to more severe wear. The cartilage friction coefficient exhibited varying degrees of dependence on pressure and speed at different periods, suggesting that superficial zone damage might cause a shift in the lubrication state of the cartilage. Furthermore, on the basis of the observed cartilage wear parameters and morphological features, we further confirmed that fatigue wear is the primary wear mode and proposed a numerical model for predicting cartilage wear volume on the basis of the degree of damage. These findings emphasize the importance of protecting and restoring the superficial zone in cartilage repair and regeneration strategies.