Photodegradation as a mechanism for controlled drug delivery.

A drug-releasing model compound based on photosensitive acrylated ortho-nitrobenzylether (o-NBE) moiety and fluorescein was synthesized to demonstrate photolysis as a mechanism for drug release. Release of this model compound from a hydrogel network can be controlled with light intensity (5-20 mW/cm(2)), exposure duration (0-20 min) and wavelength (365, 405, 436 nm). Due to the high molar absorptivity of the compound (5,984 M(-1) cm(-1)), light attenuation is significant in this system. Light attenuation can be used to self-limit the dosing from a hydrogel, and allow subsequent release from the drug reservoir after equilibration, or attenuation can be utilized to create a chemical gradient within the hydrogel. A model of photodegradation that uses an integrated form of Beer-Lambert's law quantitatively predicts release from hydrophilic hydrogels with low crosslink density, but fails to quantitatively predict release from more hydrophobic systems, presumably due to partitioning of the hydrophobic model compound in the hydrogel. In contrast to other mechanisms of release (enzymolysis, hydrolysis), photolysis provides real-time on demand control over drug release along with the unique ability to create chemical gradients within the hydrogel.