Preparation and Timed Release Properties of Self-Rupturing Gels

Swelling of polymeric hydrogels is sensitive to their cross-link densities. Here, we exploit this principle to prepare self-rupturing gels which are based on a commonly-used, nontoxic, and inexpensive polyelectrolyte, poly­(acrylic acid), and are prepared through a simple and low-cost polymerization-based technique. The self-rupture of these covalently cross-linked gels is achieved by preparing them to have highly nonuniform cross-link densities. This heterogeneity in cross-linking leads to highly nonuniform swelling, which generates stresses that are high enough to induce gel rupture. The time required for this rupture to occur depends on the difference in the cross-link densities between the adjoining gel regions, gel size, order in which the variably cross-linked gel portions are synthesized, and on the ambient pH and ionic strength. Furthermore, when these self-rupturing gels are prepared to have liquid-filled (capsule-like) morphologies, they can act as timed/delayed release devices. The self-rupture of these capsules provides a burst payload release after a preprogrammed delay, which is on the timescale of days and can be easily tuned by varying the rupture time, i.e., by varying either the cross-link nonuniformity or the pH and ionic strength of the release media.