Comparative rheological behavior of hyaluronan from bacterial and animal sources with cross-linked hyaluronan (hylan) in aqueous solution

Using a variety of rheological techniques. the behavior of hyaluronan (M-w 0.8-2.2 x 10(6)), cross-linked hyaluronan (hylan) (M-w 1.8-12.5 x 10(6)), a nd Healon (M-w similar to 5 x 10(6)) (a proprietary hyaluronan) was studied over a large range of molecular weights. The object was to study the effec t of the cross-links in hylan on the various rheological parameters, in com parison with linear hyaluronan. There are significant differences. The Hugg ins constant and the critical overlap parameter C*[eta] are considerably lo wer for hylan and an increase in moduli at low frequencies was observed for hylan compared with the hyaluronan samples at all molecular weights studie d. The results point to a difference in structure in dilute solution for hy lan due to the ability to form networks, which can be removed by pressure f iltration. In contrast, we do not find an increase of the steady shear visc osity and elastic modulus at higher concentrations when a homogeneous entan gled network is reached. We attribute this behavior to the semirigid charac ter of the hyaluronan chain and to the predominance of entanglements over t he cross-link points present in hylan in the semidilute domain. Due to the higher apparent molecular weights that are possible with hylan structures b ut not with the hyaluronans currently available, a wider range of applicati ons can be achieved with hylans when viscoelasticity is required, particula rly for the viscosupplementation of synovial fluid damaged by osteoarthriti s. (C) 2001 John Wiley & Sons, Inc.