Effects of low tangential permeability in the superficial layer on the frictional property of articular cartilage

The biphasic characteristics of articular cartilage are known to play important roles in cartilage lubrication. However, it is still difficult to biotribologically explain the extremely low friction coefficient observed in articular cartilage. Previous studies have indicated that the surface layer of articular cartilage includes tangentailly-aligned dense collagen fibers while permeability of articular cartilage in tangential direction is dramatically reduced in response to compressive strain. Therefore, we hypothesized that the anisotropic structure and property in articular cartilage surface improve the lubrication and frictional properties. A fiber–reinforced poroelastic biphasic model was developed in Abaqus to determine the effect of low tangential permeability on the frictional property of articular cartilage. In the model, the tangential permeability in the superficial layer of 100 μm in thickness was reduced to 1/10 as compared with normal permeability. Results revealed that the permeability-reduced superficial layer plays an important role in decreasing friction coefficient in articular cartilage and the role is more significant in slower friction including the start-up friction. Results also revealed that there is a positive effect of the thickness of the low permeability layer on the start-up friction property, while the effect was almost negligible on the dynamic friction property.