Synthesis and characterization of dextran-maleic acid based hydrogel.

A new class of hydrogel precursor, dextran-maleic acid (Dex-MA), was synthesized by the reaction of dextran with maleic anhydride in the presence of the catalyst triethylamine. The effects of temperature, time, catalyst amount, and reactant concentration on the degree of substitution (DS) by MA was studied to establish an optimum reaction condition. The new hydrogel precursor had excellent solubility in various common organic solvents. The hydrogels based on Dex-MA precursor were made by the irradiation of Dex-MA with a long wave UV lamp. The Dex-MA hydrogels showed a very high swelling ratio in water, and the magnitude of swelling depended on the pH of the medium and the DS by MA. The Dex-MA hydrogels exhibited the highest swelling ratio in neutral pH, followed by acidic (pH 3) and alkaline pH (10). The most distinctive characteristic of Dex-MA hydrogels was that a carboxylic acid group was generated by the reaction of dextran with maleic anhydride. As a result, the swelling ratio increased with an increase of the DS of the MA segment (ionizable moiety that affects swelling ratio) in the Dex-MA hydrogel.