Novel pH-sensitive chitosan hydrogels: swelling behavior and states of water

Physically crosslinked chitosan hydrogels were synthesized by grafting D,L- lactic acid (LA) and/or glycolic acid (GA) with different feed ratios. The physical crosslinking was formed due to the hydrophobic side chains aggrega tion and intermolecular interactions through hydrogen bonds between side an d main chains. The crystallinity of original chitosan decreased by grafting LA and GA. The structural change of the hydrogels in different pH buffers was characterized by FT-IR method and the results were interpreted. Differe ntial scanning calorimetry (DSC) was used to probe the states of water in t he chitosan hydrogels. Three types of water were found in the samples, i.e. freezing water (namely free water), non-freezing water (namely bound water ), and freezing bound water, while there are variations in the amount of bo und water for different hydrogels. The effect of hydrophobic side chains on water state and swelling behavior were discussed. (C) 2000 Published by El sevier Science Ltd. All rights reserved.