Rheological properties of gels formed by physical interactions between hyaluronan and cationic surfactants.

The aim of this paper is the rheological characterization of the concentrated, gel-like phase, which arises from mixed solutions of sodium hyaluronate and oppositely charged surfactant above its critical micellar concentration. The effects of hyaluronan molecular weight (from 300 to 2kDa) and the concentration of initial solutions (0.5 and 2% for hyaluronan, 50 or 200mM for surfactant) were investigated. All systems demonstrated viscoelastic properties which can be modified over a broad range of several decades of both storage and loss moduli by the hyaluronan molecular weight and initial concentrations. The characteristic relaxation time increased with the molecular weight of hyaluronan at constant initial composition. The effect of molecular weight on characteristic moduli was dependent on initial composition - the modulus increased with molecular weight for systems with 50mM of the surfactant and decreased for the other systems. Whereas no correlation was found between gel rheological properties and the surfactant:hyaluronan charge ratio, the properties were sensitive to structural features of surfactant molecules, particularly when low and moderate hyaluronan molecular weight was used.