Release of model compounds from "plum-pudding"-type gels composed of microgel particles randomly dispersed in a gel matrix

A novel gel structure called the "plum-pudding" gel was described by us previously. I The gel was composed of randomly dispersed microgel particles ("plums") in a conventional hydrogel network. Depending on the preparation conditions, the microgels can be incorporated into the gel as expanded networks or dense collapsed globules. Where the microgel particles exist as collapsed globules, they have the potential to act as reservoirs for hydrophobic solutes, from which the solutes are released very slowly. The release of two model hydrophobic compounds (pyrene and BODIPY) from "plum-pudding" gels composed of 50:50 BAM:NIPAM microgels embedded in NIPA gel films was investigated. The release of pyrene was found to follow Fickian diffusion, while the release of BODIPY was found to be slightly non-Fickian. Thus, we propose that by controlling the attractiveness of the microgel particles to the solutes to be released, a range of release profiles can be obtained from pure-Fickian to almost any conceivable time scale.