Novel pH, ion sensitive polyampholyte gels based on carboxymethyl chitosan and gelatin

Natural pH and ion sensitive polyampholyte gels were successfully prepared by blending carboxymethyl chitosan (CM-chitosan) and gelatin using glutaraldehyde as crosslinking agent. Their swelling behaviour under the influence of pH and ionic strength of the solution has been studied, and molecular interaction and, morphology of the gels were investigated by infrared spectroscopy and scanning electron microscopy. At the isoelectric point (IEP) the blend gels shrunk most, and when pH deviated from the IEP they behaved as polycations or polyanions. A decrease in swelling degree (D-s) with rising NaCl concentration up to 0.15 M was observed for all gels, while addition of Ca2+ made them shrink due to formation of Ca2+ crosslinked bridges. The blended gels showed increasing sensitivity to pH and ionic strength as the weight fraction of CM-chitosan increased. Two essential components seem to regulate the swelling behaviour of blended gel: the first is related to osmotic pressure difference caused by the redistribution of mobile ions; the second is related to the possible formation of interactions corresponding to hydrogen bonding and hydrophobic interactions. (C) 2003 Society of Chemical Industry.