Abstract
The aim of this study is to understand the mechanisms of wear reduction of PVA(poly(vinyl alcohol) hydrogel through in situ observation of forming boundary film composed of synovia constituents on the rubbing surface. In this study, reciprocating tester was constructed on the stage in inverted fluorescent microscope. A sliding pair of a spherical reciprocating upper specimen of PVA hydrogel and flat stationary lower specimen of cover glass was prepared. Solution of 0.5wt% sodium hyaluronate (HA) was used as base lubricant and fluorescent-labeled albumin and γ-globulin were used as additives. Rubbing surface was observed through a cover glass of lower specimen and images of rubbing surface were recorded at periodic interval. Lubricants with single protein showed that albumin adsorbed loosely on rubbing surface, whereas γ-globulin adsorbed tightly. When both of albumin and γ-globulin were added to lubricants, thickness of adsorbed layer was increased as compared to that for protein solutions without HA, and lubricant with 1:2 ratio of albumin to γ-globulin at total concentration of 2.1wt% formed the most uniform and stable boundary film. In addition, lubricants in which uniform boundary film was formed showed lower friction coefficient. These results indicate that coexistence of HA and proteins accelerate the formation of boundary film and it is considered that uniform boundary film that is effective in lowering friction is formed in lubricant with appropriate constituents.
