Structural change and swelling mechanism of pH-sensitive hydrogels based on chitosan and D,L-lactic acid

Graft copolymerization of D,L-lactic acid (LA) onto chitosan (CS) was attem pted without using a catalyst, pH-sensitive hydrogels were obtained which a re based on two different components: a natural polymer and a synthetic pol ymer. These polyester substituents provide the basis for hydrophobic intera ctions that contribute to the formation of hydrogels. The swelling mechanis ms in enzyme-free simulated gastric fluid (SGF, pH 2.2) or simulated intest inal fluid (SIF, pH 7.4) at 37 degrees C were investigated. Meanwhile, stru ctural changes of the graft copolymers in the different pH buffers were stu died by FTIR, and these are discussed together with the swelling mechanisms . The effect of pH on the water uptake of hydrogel was investigated by usin g McIlvaine buffer with the same ionic strength. The morphological change o f hydrogels in different aqueous solutions is investigated by scanning elec tron microscopy (SEM). (C) 1999 John Wiley & Sons, Inc.