pH-sensitive hydrogels composed of chitosan and polyacrylamide - Preparation and properties

Three types of polymer networks of chitosan and polyacrylamide (PAAm) - semi-interpenetrating networks (semi-IPNs) of chitosan and crosslinked PAAm (net-PAAm-l-chitosan), semi-IPNs of PAAm and crosslinked chitosan (net-chitosan-l-PAAm), and interpenetrating networks (IPNs) of crosslinked chitosan and crosslinked PAAm (net-PAAm-net-chitosan) were prepared. Chitosan, in a two-fold molar excess to PAAm, provided pH-sensitivity to hydrogel networks. The amount of the crosslinking agent did not have much influence on the microhardness of network films, while higher contents of PAAm increased it. The equilibrium degree of swelling of the hydrogels had the highest values at pH 4 and decreased on increasing pH (pH 7, pH 9) or the ionic strength of the medium as well as with increasing of the degree of crosslinking. The networks in which chitosan was crosslinked, - semi-IPNs net-chitosan-l-PAAm and IPNs net-chitosan-net-PAAm, showed five cycles of completely reversible swelling.