Drug release from hydrogel devices with ratecontrolling barriers

Zero order release of a drug from monolithic polymer devices fails because the drug concentration gradient within the matrix falls with time. In principle, it should be possible to maintain this concentration gradient constant via the introduction of a ratelimiting barrier to solute diffusion at the surface of the device. In this study, progesterone-dispersed monolithic devices were prepared from either polyhydroxyethyl methacrylate (HEMA) or a copolymer of HEMA and methoxyethoxyethyl methacrylate (MEEMA). These monolithic devices were soaked in an ethanol solution of ethylene glycol dimethacrylate (EGDMA) followed by exposure to UV light to create a crosslinked zone at the outer edge. The cross-linked zone has a much lower permeability to solute than the central region of the device and therefore serves as a rate-limiting barrier. Progesterone release studies demonstrated a zero order release from devices with the crosslinked outer layer. Drug release rates were dependent upon the UV treatment time, the EGDMA concentration, and the device soaking time in the EGDMA solution.