Degradation and Release Behavior of Dextran-Based Hydrogels

Dextran hydrogels were prepared by radical polymerization of aqueous solutions of glycidyl methacrylate-derivatized dextran (dex-MA), hydroxyethyl methacrylate-derivatized dextran (dex-HEMA), and HEMA−oligolactate-derivatized dextran (dex-lactateHEMA), using potassium peroxydisulfate and N,N,N‘,N‘-tetramethylethylenediamine (TEMED) as the initiating system. Dex-MA hydrogels only degraded under extreme conditions (100 °C, pH 1−3), whereas hydrogels derived from dex-HEMA or dex-lactateHEMA degraded fully at pH 7.2 and 37 °C, due to hydrolysis of the lactate and/or carbonate esters in the cross-links. The degradation time of these gels can be tailored from 2 days to more than 2 months by varying the nature of the spacer, the degree of substitution of dextran (DS), and the initial water content of the hydrogels. The release kinetics of a model protein, Immunoglobulin G, from dex-(lactate)HEMA hydrogels were investigated and shown to be dependent on both the DS and the initial water content of the gel. Under certain conditions zero-order release was observed over a period of 10 days.