Stimuli-responsive chitosan-graft-poly(N-vinylcaprolactam) as a promising material for controlled hydrophobic drug delivery

A novel type of pH- and thermo-responsive copolymer, chitosan-graft-poly(N-vinylcaprolactam) (chitosan-g-PNVCL), was prepared by grafting carboxyl-terminated poly(N- vinylcaprolactam) (PNVCL-COOH) chains onto a chitosan backbone as a drug-delivery carrier. The formation of chitosan-g-PNVCL was confirmed by FT-IR and H-1 NMR techniques. Chitosan-g-PNVCL showed a definite phase transition at 32 degrees C as occurs in pure PNVCL. The swelling degree of the chitosan-g-PNVCL beads was found to be higher at pH 2.2 than at pH 7.4. Moreover, the swelling degree of the beads decreased with increased environmental temperature. Compared to the chitosan beads, the release profile of chitosan-g-PNVCL beads showed a slower and more controlled release of the entrapped ketoprofen. The release behavior of the chitosan-g-PNVCL beads was influenced by both the pH and temperature of the medium. The MTT assay showed no obvious cytotoxicity of chitosan-g-PNVCL against a human endothelial cell line over a concentration range of 0-400 mu g center dot mL(-1). These results suggest that chitosan-g-PNVCL could be a potential stimuli-responsive material for controlled drug delivery, and it may improve the bioavailability, efficacy, and compliance of the encapsulated drugs.