Abstract
The dependence of the intrinsic viscosities ([η]) of seven well-characterized sodium hyaluronate (HA) samples in 0.2 M NaCl solution on shear rates (γ^^·) was investigated using four kinds of viscometers with γ^^· values ranging from 0.1 to 2000 s-1. Molecular weight distributions of these samples were checked by a gel permeation chromatograph connected to a low-angle laser light scattering photometer. The determination of [η] at zero shear rate ([η]0) for high molecular weight HA had to be made using low shear viscometers with γ^^·<250s-1, since [η] showed remarkable shear thinning behavior with increasing molecular weight. Double logarithmic plots of [η]0 vs. Mw (the weight-average molecular weight) for HA in 0.2 M NaCl solution gave a relation expressed by [η]0=1.99×10-4·M0.829w for Mw≥40×104, where [η]0 was written in dl/g unit. The shear thinning behavior of [η] of HA in the solvent was analyzed by the Rouse-Zimm bead-spring model proposed by Fixman. Consequently, the γ^^·-dependence of HA in 0.2 M NaCl solution could be well described by this model of large viscosity expansion factors, and suggested that an HA chain in the solvent is a fairly expanded random coil by excluded volume effects.
