Rheological evidence of the gelation behavior of hyaluronan–gellan mixtures

It was found that solutions of calcium hyaluronate (CaHA) (0.1∼0.5 wt%) could form a gel by mixing with solutions of sodium type gellan (0.1∼0.5 wt%), although neither polymer by itself forms a gel at low concentrations (0.1∼0.5 wt% in this experiment). The rheological properties of CaHA–gellan mixtures were investigated by dynamic and steady shear measurements. Both storage shear modulus G′ and loss shear modulus G″ for CaHA–gellan mixtures increased with increasing time, and tended to an equilibrium value after 1 h. After reaching steady values of G′ and G″, the frequency dependence of G′ and G″ was observed. G′ was always larger than G″ in the accessible frequency range from 10⁻² to 10² rad/s. The effects of pH and calcium ions were examined. Gel formation of the mixtures was promoted by decreasing pH and adding from 0.01 to 0.1 M calcium ions, but excessive calcium ions weakened the gel.