ABSTRACT

Chitosan/poly(vinyl alcohol) interpenetrating polymer network type (IPN) superporous hydrogels were prepared using a gas foaming/freeze-drying method. A gas blowing method using bicarbonate as a foaming agent was applied to introduce the porous structure. Gelation kinetics was measured to determine the optimum introduction time for adding the blowing agent. Their swelling behaviors in acidic solution were studied to investigate their application as gastric retention device. The effect of the strengthener, poly(vinyl alcohol) (PVA), on the swelling and mechanical behavior of the superporous hydrogels was investigated. The introduction of a small amount of PVA significantly enhanced the mechanical strength but reduced the swelling capacity. The number of freezing/thawing (F/T) process had a significant effect on the physical properties of the chitosan/PVA superporous hydrogels, because of the formation of hydrogen bonds between the PVA molecules as a result of the number of F/T cycles. Swelling behaviors were significantly affected by crosslinking density. The increase in mechanical strength accompanied by the decrease in swelling kinetics was caused by the generation of smaller pores during the gelation process of the reactant systems associated with a higher solution viscosity. The prepared superporous hydrogels were highly sensitive to pH of swelling media and swelled only in acidic pH. Hence these superporous hydrogels could be used for gastric retention application.