Micro- and nanoscopic biotribological behaviours in natural synovial joints and artificial joints

To maintain low friction and low wear in natural synovial joints and joint prostheses with artificial cartilage, adsorbed film formation at micro- and nanoscopic levels appears to play an important role in mixed or boundary lubrication regime where local direct contact occurs. In natural synovial joints, the lubricating gel film is likely to preserve low friction and to protect the bulk cartilage even after the removal of the adsorbed film. For poly (vinyl alcohol) (PVA) hydrogel as artificial cartilage without lubricating gel layer, the adsorbed film is a single protective barrier. In the previous researches on the rubbing pair of PVA against itself or glass plate, the coexistence of albumin (A) and γ-globulin (G) as A:G = 1: 2 at total protein concentration of 2.1 wt% in hyaluronate solution showed the lowest wear. In this study, in situ observation of adsorption of proteins was conducted to clarify the dynamic changes in adsorptional behaviours in lubricants containing different protein constituents. In the mixed lubrication regime, the coexistence of albumin and γ-globulin as A:G = 1:2 showed the lowest friction. The role of appropriate constituents of proteins is discussed on low friction and low wear at micro- and nanoscopic levels on the basis of previous and present results.