Friction and Lubrication of Articular Cartilage in Mild Conditions

In this work, we investigated the frictional behavior of the articular cartilage using surface force apparatus (SFA) in mild conditions such as the slow driving speed (0.3~60 μm/s) and the low pressure (0.1~2 atm). Specific enzymes (Hyaluronidase, Type II Collagenase and Chondroitinase ABC) are treated for further investigation of the role of each component (Hyaluronic acid, collagen and glycosaminoglycans). Cartilage surface was also imaged using light interferometer to quantify the roughness changes after digestion and shearing.

We observed stick-slip friction in articular cartilage for the first time, in a certain range of loads and speeds. We introduced ‘Dynamic (friction) phase diagram’ to visualize load and speed regimes of stick-slip friction. Significant increase in friction force was observed after digestion (~2 times for Hyaluronidase, ~5 times for Collagenase and ~10 times for Chondroitinase ABC) with apparent roughening (Hyaluronidase and Chondroitinase ABC) or smoothening (Collagenase) of cartilage surface. Moreover, we found that there is minor contribution of topography (roughness) to frictional behavior of articular cartilage.