Surface-preferential crosslinking in hydrogels to minimize the burst effect and design tunable lag times for drug delivery

Hydrogels based on poly(vinyl alcohol) and poly(2-hydroxyethyl methacrylate) typically show an initial burst. When treated with glutaraldehyde to form a highly crosslinked network at the surfaces of the gels, the burst effect was minimized and effectively controlled. The effect of polymer type, crosslinking solution concentration, time exposed to glutaraldehyde, and sample geometry on the release behavior of proxyphylline, a small molecular weight model drug, were investigated. Highly concentrated glutaraldehyde solutions led to a delayed release, but in each case the amount of drug removed by extraction during the crosslinking step was minimal. Drug delivery using this technique effectively reduced the burst without significantly impacting the steady state release rate.