Preparation and characterisation of a Hydrogel from low-molecular weight hyaluronic acid

A relatively low molecular-weight HA (Hyaluronic Acid) has been chemically stabilized by means of a crosslinking reaction with water-soluble carbodiimide (WSC) and L-Lysine methyl ester in water solution to form a chemical hydrogel. FTIR analysis performed both on the precursors and on the crosslinked hydrogel, indicated the formation of ester bonds between different HA molecules that led to an intermolecular crosslinking. Hydrogel swelling properties as well as equilibrium sorption properties were evaluated. A swelling ratio of 250 was observed after immersion in distilled water for 7 hr. Rheological measurements by means of a plate-plate rheometer of the the crosslinked showed non-Newtonian and pseudoplastic behaviour, while the uncrosslinked HA showe a viscous characteristic. Morphological analysis of these miro-structure by a scanning electron microscope indicated that the freeze-dried crosslinked hydrogel presents a more closed pore structure and higher density of pores than the freeze-dried original HA.