The present study introduces a tribological comparison of five polyvinyl alcohol (PVA) hydrogel specimens with different physiological properties and possible candidate materials for cartilage replacement. The superior lubrication of articular cartilage is believed to lie in solid-to-solid molecular interactions. Therefore, the focus was paid to the investigation of boundary lubrication with regard to interstitial fluid flow reduction. The experiments were carried out in a ball-on-plate (glass-on-hydrogel) configuration. Based on the experiments, we proposed a boundary lubrication mechanism, selected a hydrogel with the least surface damage, and highlighted the desired properties that should be considered when developing the artificial cartilage.

Hip joint replacements represent the most effective way of treatment for patients suffering from joint diseases. Despite the rapid improvement of implant materials over the last few decades, limited longevity associated with wear-related complications persists as the main drawback. Therefore, improved tribological performance is required in order to extend the service life of replacements. The effect of surface texturing of ultra- high molecular weight polyethylene (UHMWPE) acetabular cup was investigated in the present study. Unique tilling method was utilized for manufacturing the dimples with controlled diameter and depths on the contact surface of the cup. The experiments with four commercial femoral components and two model lubricants were realized. The main attention was paid to a coefficient of friction considering the differences between the original and the dimpled cups. Results showed remarkable lowering of friction, in general. Focusing on the simulated human synovial fluid, friction was reduced by 40% (alumina ceramic), 38.8% (zirconia toughened ceramic), 25.5% (metal), and 9.9% (oxinium). In addition, the dimples helped to keep the friction stable without fluctuations. To conclude, the paper brings a new insight into frictional behaviour of the hip replacements during running-in phase which is essential for overall implant lifespan. It is believed that proper surface texturing may rapidly improve the life quality of millions of patients and may lead to considerable financial savings.