Tribology of enzymatically degraded cartilage mimicking early osteoarthritis

Healthy cartilage is a water-filled super lubricious tissue. Collagen type II provides it structural stability, and proteoglycans absorb water to keep the cartilage in a swollen condition, providing it the ability to creep and provide weeping lubrication. Osteoarthritis (OA) is a degenerative and debilitating disorder of diarthrodial joints, where articular cartilage damage originates from enzymatic degradation and mechanical damage (wear). The objective of this research is to observe the level of cartilage damage present in knee arthroplasty patients and to understand the friction and creep behavior of enzymatically degraded bovine cartilage in vitro. Lateral (Lat) and medial (Med) condylar cartilages from OA patients undergoing total knee arthroplasty showed signs of enzymatic degradation and mechanical damage. Bovine cartilages were exposed to collagenase III and chondroitinase ABC to degrade collagen and proteoglycans, respectively. The loss of proteoglycans or collagen network and morphological changes were observed through histology and the atomic force microscope (AFM), respectively. A significant effect on creep due to enzymatic treatment was not observed. But the enzymatic treatment was found to significantly decrease the coefficient of friction (COF) at 4 N, while higher COF was shown from chondroitinase ABC degraded cartilage at 40 N. Collagenase III treatment leads to the release of intact proteoglycans at the sliding interface, while chondroitinase ABC treatment leads to the loss of chondroitin sulfate (CS) from the proteoglycans. Chondroitinase ABC-digested bovine cartilage mimicked patient samples the best because of the similar distributions of proteoglycans, collagen network, and friction behavior.