Material PerformanceFITC-dextran releases from chitosan microgel coated with poly(N-isopropylacrylamide-co-methacrylic acid)

Cross-linked chitosan microgels were prepared by a spray drying method while varying the ratio of the cross-linking agent (glutaraldehyde) to the chitosan. The microgels were then coated with poly (N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) by electrostatic interaction. Both the interaction of chitosan and P(NIPAM-co-MAA), and the amount of the copolymer adsorbed on the microgels showed the highest levels at approximately pH 6.0. The maximum amount of copolymer adsorbed on the microgels with a lower cross-link density (0.73 g/g) was higher than the amount on the microgels with a higher cross-link density (0.36 g/g), mainly because the swelling ratio of the microgels with a lower cross-link density was higher and because more surface area was available for the adsorption. The degree of release of FITC-dextran was higher at pH 4.0 than at pH 8.0, possibly due to the swelling of the cross-linked chitosan core of the microgels. The release from the microgels was effectively suppressed by the phase transition of the P(NIPAM-co-MAA) shell at pH 4.0 when the temperature was higher than the lower critical solution temperature (around 31 °C) of the copolymer.