Fig. 1.

The effect of HA digestion on the friction force between cartilage and glass in PBS. Step-load experiment showing how the friction force, F, and the friction coefficient, μ, changes with time, t, and following the in situ digestion of HA under a normal load of 170 mN, sliding velocity of approximately 50 μm/s, and peak-to-peak sliding amplitude of approximately 500 μm. The solid line at the top is the average friction coefficient of grafted HA gel on mica surfaces under similar load and shear conditions reported in ref. 4, shown for comparison. Solid lines indicate equilibrium values.