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, η 0 , the steady shear compliance, J   e 0and Δη defined as Δη = η 0 − η a (∞), where η a (∞) 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 M v < 35 × 10 4 HA chains are dispersed molecularly in solution; (II) 35 × 10 4 < M v < 100 × 10 4 , the polymer chains form a weak entanglement network observed only through η 0 (HI) 100 × 10 4 < M v < 160 × 10 4 , the network is strengthened with increasing molecular weight and becomes detectable through both η 0 and J   e 0and also through the overshoot phenomenon; and (IV) 160 × 10 4 < M v , the network is “saturated” or “completed” dynamically. This is the conjecture presented for the first time by the present work.