Temporary network formation of hyaluronate under a physiological condition. 1. Molecular-weight dependence

The dynamic shear moduli at various frequencies and stress growth after the sudden start of steady shear were measured for 1% HA (hyaluronic acid) solutions with different molecular weights. From the results of the zero shear viscosity, eta 0, the steady shear compliance, J 0e, and delta eta defined as delta eta = eta 0 - eta a (infinity), where eta a (infinity) is the apparent viscosity at the steady state, it was shown that the molecular mechanism of flow of 1% HA solutions was classified into four regions with respect to molecular weight: (I) the viscosity-average molecular weight Mv less than 35 X 10(4), HA chains are dispersed molecularly in solution; (II) 35 X 10(4) less than Mv less than 100 X 10(4), the polymer chains form a weak entanglement network observed only through eta 0; (III) 100 X 10(4) less than Mv less than 160 X 10(4), the network is strengthened with increasing molecular weight and becomes detectable through both eta 0 and J 0e and also through the overshoot phenomenon; and (IV) 160 X 10(4) less than Mv, the network is "saturated" or "completed" dynamically. This is the conjecture presented for the first time by the present work.