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

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Abstract
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, η0, the steady shear compliance, J and Δη defined as Δη = η0 − ηa (∞), where ηa(∞) 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 < 35 × 104 HA chains are dispersed molecularly in solution; (II) 35 × 104 < Mv < 100 × 104, the polymer chains form a weak entanglement network observed only through η0 (HI) 100 × 104 < Mv < 160 × 104, the network is strengthened with increasing molecular weight and becomes detectable through both η0 and J and also through the overshoot phenomenon; and (IV) 160 × 104 < Mv, the network is “saturated” or “completed” dynamically. This is the conjecture presented for the first time by the present work.