In situ atomic force microscopy measurement of the dynamic variation in the elastic modulus of swollen chitosan/gelatin hybrid polymer network gels in media of different pH

The surface morphology and elastic modulus of chitosan/gelatin hybrid polym er network (CS/GLN HPN) gels was investigated by in situ atomic force micro scopy (AFM). The surface domains of hydrogel varied from irregular clumps t o sponge-like patterns with increasing swelling time. The vertical height a nd width of the surface domains observed in alkali medium are smaller than in acidic medium. The indentation of the gels caused by the AFM tip increas ed with time and the elastic modulus of the gels estimated by the Hertz mod el decreased sharply compared with that of xerogel. In alkali medium, due t o the reassociation of hydrogen bondings between networks, the elastic modu lus increased slightly. (C) 1999 Society of Chemical Industry.