Lubrication within hip replacements - Implication for ceramic-on-hard bearing couples.

The objective of the present study is to clarify the lubrication processes within artificial joints considering the ceramic femoral heads focusing on the role of particular proteins. Two optical methods were employed; colorimetric interferometry and fluorescent microscopy. The experiments were conducted in ball-on-disc configuration, where the ball is made from ceramic (Sulox(TM), BIOLOX(®)delta) and the disc from optical glass. The measurements were realized under pure rolling, partial negative and partial positive sliding, to get a complex information about the protein film behaviour under various conditions. Moreover, two different speeds were investigated; 5.7 and 22 mm/s, respectively. The contact was lubricated by saline solutions containing albumin and γ-globulin in a ratio 2:1, while the total protein concentration was 10.5 mg/ml. Under pure rolling conditions, the film thickness gradually increases with time/rolling distance independently of material and rolling speed, while the dominant fluid constituent is albumin. In the case of negative sliding, the film formation is time/distance/speed dependent. At lower speed, both proteins contribute to film thickness; at higher speed, the effect of γ-globulin is not substantial. When the disc is faster, the character of film formation is similar to the metal component in the case of Sulox ceramic. Biolox ceramic shows a different behaviour, while for both materials, the contribution of γ-globulin increases with increasing speed. As most of the results can be well explained in terms of specific proteins, it can be concluded that the experimental approach is suitable for the investigation of protein film formation considering the ceramic materials.