Characterization of hyaluronic acid by dynamic light scattering and rheological techniques

Hyaluronic acid (HA) solutions represent an important class of biomedical products, mostly used in viscosupplementation of joints and as fillers. In the present work the hydrodynamic and rheological properties of hyaluronic acid, of differing M¯_W(90-4000 kDa), in physiological saline were investigated. Firstly, the effective conformation taken by the polymer chains was studied using dynamic light scattering. It was observed that they behaved like random coils which dimension is higher increasing the molecular weight of the material. Secondly, combining a novel microrheological technique, based on the dynamic light scattering of tracer particles, with conventional rheometry, it was possible to study in which way the molecular weight and the concentration of the polymer influence the storage modulus (G'), loss modulus (G") and complex viscosity (η*) of its solutions, over an extended frequency range (typically 0.01-10000 Hz). This extended characterization allowed determination of the mesh size ξ of the physical network, created by the entangled polymer chains. Calculated mesh sizes in the range 200-700 nm were observed, demonstrating the possibility to use these systems as injectable carriers of biomolecules with an appropriate dimension.