Effect of Rotational and Sliding Motions on Friction and Degeneration of Articular Cartilage under Dry and Wet Friction

Understanding the tribological properties of articular cartilage allows scientists to evaluate degenerative joint diseases and develop new treatment techniques. The objectives of this study are to demonstrate the detrimental effect of rotational motion under both dry and wet friction and to evaluate the friction and wear behavior of bovine articular cartilage with sliding and rotational testing configurations that represent fluid film and boundary lubrication mechanisms, respectively. The articular cartilage pin and plate samples were harvested from healthy adult bovine and then tested on a self-made friction and wear simulator. Cartilage samples were subjected to sliding and rotational motions under constant load. Friction coefficients and wear factors were calculated under three conditions: using bovine serum, phosphate buffered saline and with no lubricant present. The friction coefficient and wear factor of the articular cartilage were significantly increased with rotational motion under both dry and wet friction. Using bovine serum as lubricant in the sliding testing configuration the friction coefficient and wear factor of articular cartilage were both decreased. A similar decrease in the tribological properties of cartilage was initially observed for the rotational testing configuration with bovine serum; however, the friction coefficient and wear factor were increased after 150,000 cycles. In the absence of lubricant, the articular cartilage was entirely worn on contact area in both sliding and rotational testing configurations. Bovine serum proved an effective fluid film lubricant for articular cartilage surfaces.