The effects of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel on microspheres preparation or drug release were studied. The rate of gelation is zero order corresponding to the chitosan concentration but non-zero order corresponding to the glutaraldehyde concentration. It was suggested that the cross-linking reaction was mainly dominated by the concentration of small molecule reactant, glutaraldehyde. The relaxation of an entangled polymer chain in a gel network as a result of the swelling of cross-linked chitosan hydrogel was investigated by the stress-strain determination. The higher the cross-linking density of chitosan hydrogel, the lower the swelling ability of chitosan hydrogel due to the slower relaxation rate of polymer chain, which then results in the decreased drug-release rate.
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