Experimental investigation of the dynamic properties of natural cartilage under reciprocating sliding at two typical rubbing pairs

Abstract

Natural cartilage is a multiporous viscoelastic biological material with extremely high water content and a macroscopically curved surface. Due to the sampling frequency limitations of typical data systems, the dynamic properties of the contact of cartilage against other surfaces, including rubbing surface characteristics and coefficient of friction, is still not completely understood. In this study, cartilage samples were retrieved from 18- to 24-month-old bovine femora. Contact displacement and coefficient of friction of two typical rubbing pairs of for cartilage-on-glass and cartilage-on-cartilage were recorded using a UMT-2 testing rig using a high sampling frequency data system. A five-point sliding average method was adopted to analyze the experimental data. The results showed that contact displacement comprised cartilage deformation and nominal rubbing profile. Cartilage deformation increased nonlinearly with time while nominal rubbing profile was associated with the rubbing configuration and appeared to be a factor in the low surface sample configuration. Higher cartilage deformation resulted in more load being carried by the solid phase and coefficient of friction with the time as a whole, but the surface characteristics played a role in determining the coefficient of friction in the cartilage-on-cartilage configuration but a lesser role for cartilage-on-glass. Therefore, surface characteristics have a clear role in defining the dynamic properties of natural viscoelastic soft biological materials and these research results will help to evaluate in future the frictional properties of artificial cartilage biomaterials.