Preparation and swelling kinetics of pH-sensitive photocrosslinked hydrogel based on carboxymethyl chitosan

摘要

A series of photocrosslinkable carboxymethyl chitosans were synthesized by mixing azidobenzaldehyde and an aqueous solution of carboxymethyl chitosan. Aqueous solutions of the product were photocrosslinked via UV irradiation to afford hydrogels. The morphologies and the mechanical properties of the hydrogels were characterized. Their swelling kinetics were studied. The hydrogels displayed good pH sensitivity in pH 2.2-8.0 buffer solutions and an overshooting effect during swelling in pH <5 buffer solutions. The following three factors may contribute to this overshooting effect: firstly, because of the protonation of amide groups in the network in acidic solution, the formation of ionic bonds between amine ions and partial carboxylic ions causes the release of solvent from the swollen network; secondly, ionized carboxylic groups in the network become protonated and convert into nonionized carboxylic groups, and so the concentration of free counterions within the network gradually decreases in acidic solution, leading to solvent release; finally, hydrogen bonds gradually form between nonionized carboxylic groups on the network, which also leads to solvent release from the swollen network. In pH ≥ 5 buffer solutions, the overshooting effect disappeared and the swelling kinetics followed Schott's second-order swelling kinetics.