THE APPLICATION OF SHEAR AND EXTENSIONAL VISCOSITY MEASUREMENTS TO ASSESS THE POTENTIAL OF HYLAN IN VISCOSUPPLEMENTATION

The shear and extensional viscosity characteristics have been compared for hyaluronan and two samples of a cross-linked derivative, hylan, o f different molecular weights, While shear thinning behavior was obser ved for all systems in shear flow, strain thickening was observed in e xtensional flow for the relatively dilute systems, However, there was a progressive transition to shear thinning behavior as the polymer con centration was increased, It is evident from the results that the shea r flow techniques alone provide an incomplete picture of the rheologic al properties of these materials and that extensional flow characteris tics are potentially dominant, For example, at relatively high deforma tion rates of 500 s(-1) and above, our results show that the extension al viscosities of aqueous solutions of the various polymers are at lea st two orders of magnitude greater than their corresponding shear flow viscosities. The incremental differences in viscosity with concentrat ion increased with increasing molecular mass of the polymers and were greater in exensional flow than shear flow, These results demonstrate that the dynamic network structure formed by the higher molecular mass hylans offer potentially better physical and mechanical properties fo r visco supplementation of diseased osteoarthritis joints compared wit h the parent hyaluronan. Copyright (C) 1996 Elsevier Science Ltd