Tailoring the swelling pressure of degrading dextran hydroxyethyl methacrylate hydrogels.

Swelling pressure measurements were performed on degrading dextran hydroxyethyl methacrylate (dex-HEMA) hydrogels. In these networks, the cross-links are hydrolyzable carbonate ester bonds formed between methacrylate groups and dextran molecules. It is demonstrated that dex-HEMA gels made in the presence of a known amount of free dextran chains exhibit osmotic properties similar to those of partially degraded dex-HEMA gels. The swelling pressure, Pi(sw), of degrading dex-HEMA gels is controlled primarily by the cross-linked dex-HEMA polymer and the free dextran molecules, while the contribution of short poly-HEMA fragments (produced in the degradation process) is negligible. It is found that Pi(sw) only slightly changes during the first 15 days of degradation. Close to the end of the degradation process, however, a much faster increase in Pi(sw) is observed. The swelling pressure profile of these gels strongly depends on the concentration of the cross-linked dex-HEMA and its chemical composition (amount of HEMA groups per 100 glucose units).