ABSTRACT
The enthalpic driving force may be due to specific interactions between water and the polar groups on the polymer backbone, so the overall sorption process can be envisaged as occurring by two distinct mechanisms: absorption of water molecules on hydrophilic groups and water dissolution in the polymer matrix. Lower density means higher free volume and, therefore, higher availability of the polar groups to the water molecules. This chapter explores how the dimension and chemical structure of the substituting group alters the mechanism of water sorption by Hyaluronic acid (HA) and the consequence of this sorption on the mechanical properties of the material. The densities of the HA and the three esters were evaluated at 40°C by means of a Wesphail balance using n-hexane and chloroform as reference liquids. These two liquids were chosen because of their negligible solubility in the HA and its derivatives. Many physiological functions, HA controls the movement of fluid and macromolecules through the extracellular matrix.
