Investigation into the effects of proteins and lipids on the frictional properties of articular cartilage.

The aim of this study was to investigate the effects of the proteins and the lipids on the frictional properties of articular cartilage in the mixed and boundary lubricating regimes. Bovine articular cartilage that had been treated to remove the lipids, and cartilage that had been treated to remove the proteins, from the surface layer were studied in order to investigate differences in their lubricating abilities. Tests were carried out on a sliding friction rig under contact pressures of 0.5 and 4 MPa. The results of the friction tests carried out under the 4 MPa contact pressure showed a slight increase in friction coefficient for both the lipid and the protein deficient cartilage when compared with the control cartilage. These differences were more apparent at the shorter loading times but none of the differences were found to be statistically significant. The tests at the lower contact pressure of 0.5 MPa showed that removing the lipids by washing the surface with detergent increased the friction coefficient at the shorter loading times but had no effect at the longer loading times. Digesting the cartilage with trypsin to remove the proteins from the surface layer had no effect on the friction coefficient at the shorter loading times but reduced the friction coefficient at the longer loading times. Both these results were confirmed with specimens that had both the lipids and the proteins removed from the surface layer.