Synthesis and characterization of a pH-sensitive hydrogel made of pyruvic-acid-modified chitosan

Pyruvic-acid-type chitosan (PA-CS) was prepared by the reaction of an amine group on chitosan with a carbonyl group on pyruvic acid. Then, a novel hydrogel film was obtained via cross-linking of poly(ethylene glycol) diglycidyl ether (PEGDE) with PA-CS. 1H-NMR and FT-IR spectrometry were applied for the verification of the CS and PA-CS structure. The degree of swelling was studied by changing the molar ratio of PEGDE and PA-CS. Moreover, the swelling ratio of cross-linked membrane in different pH buffer solutions was measured. The result showed that the swelling of hydrogel exhibited obvious pH-sensitivity. The swelling ratio was higher at pH 1-4 and pH 7-12, but lower at pH 5-6.