Predictive modelling of the swelling behaviour of polyelectrolytic chitosan hydrogels

This study concerns the development of a model to predict the pH dependent swelling behaviour of a polyelectrolyte gel. Flory and Tanaka swelling theory was used to calculate a value of rswell, the swelling ratio at equilibrium. Swelling equilibrium is reached when the mixing, elastic and ionic forces in the gel are balanced. Each of these contributing factors were considered separately and the swelling ratio at which all three contributions balanced was calculated. The calculations were modelled on a chitosan–genipin/glutaraldehyde/polygenipin system, and the results were compared to experimental data. The dependence of swelling and pH and crosslinker was successfully modelled, but the absolute degree of swelling was higher than found experimentally. This is most likely because of underestimation of the elastic contribution of the non-Gaussian nature of the network chains. The information awarded by the model is valuable for the design of targeted swelling hydrogel drug delivery systems.