The effect of hydroxyl radicals on the rheological performance of hylan and hyaluronan

Shear flow, dynamic oscillation and extensional viscosity measurements were used to compare the rheological performance of several hylan samples (M-v 1.6, 3.2, 3.7, 4.7 and 5.6 x 10(6)) and hyaluronan (M-v 1.4 and 1.8 x 10(6) ) before and after hydroxyl radicals ((OH)-O-.) induced degradation. It was found that the higher molecular weight cross-linked structure of hylan was more resistant to degradation than hyaluronan and that this superior stabi lity was reflected in various rheological parameters. The (OH)-O-. degradat ion or the initial hylan and hyaluronan samples produced a range of polysac charides based on hylan and hyaluronan with molecular weight covering a ran ge from 0.5-5.6 x 10(6). The rheological parameters associated with the pol ysaccharides could then also be studied. Zero shear values of the complex v iscosity (eta*), dynamic viscosity (eta') and shear viscosity (eta) were ca lculated using the method of Morris(1) and shown to approach the same value at zero shear or frequency. An adaptation of the method of Gibbs et al.(2) gave a 'master curve' for the storage and loss modulus of hyaluronan and h ylan, which encompasses a 10-fold molecular weight and a 5-fold concentrati on variation. In all instances for hylan, the storage modulus predominates over the loss modulus, whereas for hyaluronan, the reverse is true, demonst rating the greater elasticity of hylan throughout the whole experimental ra nge of molecular weights and concentrations. (C) 2000 Elsevier Science B.V. All rights reserved.