Preparation and Characterization of a Hydrogel from Low-molecular Weight Hyaluronic Acid

A relatively low-molecular weight sample of hyaluronic acid (HA) was chemically modified by means of a cross-linking reaction with water-soluble carbodiimide and L-lysine methyl ester to form a chemical hydrogel. FT-IR analysis performed on the precursors and on the cross-linked hydrogel indicated the formation of ester bonds between different HA molecules that led to an intermolecular cross-linking. Hydrogel swelling kinetics as wen as equilibrium sorption properties were evaluated. A swelling ratio of 250 was observed after immersion in distilled water for 7 h. Rheological measurements by means of a plate-plate rheometer of the cross-linked sample showed non-Newtonian and pseudoplastic behavior, while the uncross-linked HA showed Newtonian behavior and a viscous characteristic. Morphological analysis of these microstructures by scanning electron microscopy indicated that the freeze-dried crosslinked hydrogel presents a more closed-pore structure and higher density of pores than the freeze-dried original HA.