Investigation of contact characteristics and frictional properties of natural articular cartilage at two different surface configurations.

Natural cartilage surfaces were macroscopically curved with multi-porous viscoelastic biologic materials with extremely high water, but whether curved surface configuration could play an important role on the contact and frictional properties of natural cartilages fails to be completely understood up to now. In this current study, cartilage samples came from the 18-24 month-old bovine femora. Contact characteristic and frictional properties at two cartilage configurations were investigated using the UMT-2 testing rig and the five-point sliding average method would be adopted to analyze these tested data. These results indicated the surface displacement was extremely associated with the plate cartilage surface and seemed to be a representative of cartilage surface configuration. The summit of the surface load lagged behind that of the surface displacement at the same condition. Coefficient of friction showed obviously different variation with time at two cartilage surface configurations due to the fact that these two surface displacements had different amplitudes and opposite directions as a function of the sliding length. Therefore, surface configuration played the main role on these variables of contact displacement, contact load and coefficient of friction due to the direction and magnitude of the surface displacement while applied load and sliding velocity had a secondary role. Natural cartilage surfaces were macroscopically curved with multi-porous viscoelastic biologic materials with extremely high water, but whether curved surface configuration could play an important role on the contact and frictional properties of natural cartilages fails to be completely understood up to now. In this study, two different cartilage configurations were adopted to investigate natural cartilage properties, and the five-point sliding average method would be used to analyze these tested data. These results indicated the contact displacement was consisted of cartilage deformation and surface displacement while contact load was composed of steady load and surface load (as shown in the figure, panels (a) and (b)). Surface displacement was greatly associated with the plate cartilage surface and seemed to be a representative of cartilage surface configuration. These two surface displacements had different amplitudes and opposite directions as a function of the sliding length (as shown in panel (c)). The summit of the surface load lagged behind that of the surface displacement at the same condition (as shown in panel (d)). Surface displacement and surface load in the contact characteristic of natural cartilages were extremely related with the cartilage configurations. and their correlation coefficients varied periodically with the moving time (as shown in panel (e)). Coefficient of friction showed obviously different variation with time (as shown in panel (f)). Therefore, surface configuration played the main role on these variables of contact displacement, contact load and coefficient of friction due to the direction and magnitude of the surface displacement while applied load and sliding velocity had a secondary role. Variation in contact and frictional properties of natural cartilage at two different surface configurations (a) Contact displacement and its parts varied with time; (b) Contact load and its parts varied with time; (c) Surface displacement varied with the sliding length at two CPSTs; (d) Surface load and surface displacement varied with time; (e) Variation in the relation coefficient with the moving time; (f) Coefficient of friction varied with time at two CPSTs.