Swelling Pressure Observations on Degrading Dex-HEMA Hydrogels

The variation of the swelling pressure of dextran hydroxyethyl methacrylate (dex-HEMA) hydrogels is determined as a function of the degradation time. In the first stage of the degradation process a moderate increase in the swelling pressure is observed due to the decrease of the elastic pressure. In this period the cross-link density of the polymer network gradually decreases, but only a small amount of free polymer (dextran) is released. Toward the end of the degradation process, however, a sudden increase in the swelling pressure occurs which is accompanied by the release of a major amount of dextran chains. It is demonstrated that the chemical composition of the network (dex-HEMA content and the number of HEMA groups on the dextran chains) strongly affects the degradation rate of dex-HEMA hydrogels. These observations are important to design degrading hydrogel systems with tailored swelling pressure profile for pulsed drug delivery.