Fig. 3.

(A) The effect of the load on the change in friction force, ΔF = (F_{max ,undigested-}F_{max ,digested})/F_{max ,undigested}, and observed sliding behavior. (A, Inset) The sliding behavior of the cartilage before digestion. (B, Inset) Normal load, L, and friction force, F, before and after HA digestion in a cartilage sample under a normal load of approximately 12 mN. Before digestion, the cartilage exhibits stick–slip behavior and high friction force but little evidence of surface wear or damage. After HA digestion, stick–slip behavior disappears and the friction force decreases, but frequent “wear spikes” (darts) indicate significant wear and damage.