A micro-rheological and rheological study of biopolymers solutions: Hyaluronic acid.

Hyaluronic acid (HA) solutions represent an important class of biomedical products, mostly used as viscosupplements in orthopaedics and as fillers in the cosmetic industry. The focus of the present work is the hydrodynamic, micro-rheological and rheological characterization of HA in physiological saline. Standard viscoelastic characterization techniques were coupled with micro-rheological measurements, i.e. by measuring the passive motions of particles embedded in the samples via Dynamic Light Scattering (DLS), effectively extending the accessible frequency range typical of standard rheometers. The influence of molecular weight and polymer concentration on the storage modulus (G'), loss modulus (G") and complex viscosity (η*) of HA saline solutions was investigated. A brief comparison with theoretical models was made showing such concentrated solutions to be of a semi-flexible nature. In addition, the entanglement concentration ν, the critical molecular weight M¯c, and the mesh size ξ of the physical network created by the entangled polymer chains were calculated.