Basic studies also were carried out to determine the effects of specific conditions, i.e., chemical interactions, heat and free-radical exposure, on HA vs. the cross-linked HA gel. Exposure of HA to free radicals (XO/HX, 1U/mL) caused notable degradation within 5 min, with maximum degradation after 60-90 min.28 The viscosity of the free radical-treated HA decreased to approximately that of the buffer (water) alone; i.e., 1 cps. In contrast, exposing the cross-linked HA gel to the same concentration of free radicals for 1 hr had a minimally degradative effect; a 2.3% increase in the formation of degradation products was observed, as shown by soluble, 0.2 μm filterable polysaccharide.