Preparation and characterization of N-(2-carboxybenzyl)chitosan as a potential pH-sensitive hydrogel for drug delivery.

A novel water-soluble chitosan derivative [N-(2-carboxybenzyl)chitosan, CBCS] was synthesized. The chemical structure of CBCS was characterized by FTIR, (1)H NMR and UV spectroscopies. The degree of substitution (DS) of N-2-carboxybenzyl was determined by colloid titration. In different pH buffer solutions, the swelling characteristics of hydrogels based on CBCS (CBCSG) prepared by crosslinking with glutaraldehyde have been studied. Results showed that the swelling ratio (SR) of CBCSG decreased with an increase of the amount of glutaraldehyde, and that CBCSG swelled more significantly in alkaline solution than in acidic medium, showing the lowest SR at pH5.0. The SR of CBCSG increased with the raising of the DS of the N-2-carboxybenzyl group in alkaline solution, but no significant change was observed in an acidic environment. CBCSG showed swelling reversibility when alternately soaked in pH1.0 and 7.4 buffer solutions. Release profiles of fluorouracil (5-FU), a poorly water-soluble drug, from CBCSG were studied under both simulated gastric and intestinal pHconditions. The release was much quicker in pH7.4 buffer than in pH1.0 solution. Results indicated that CBCS could be a potential pH-sensitive carrier for colon-specific drug delivery system.