Microactuators toward microvalves for responsive controlled drug delivery

A responsive controlled drug release system in which the delivery of drugs is achieved by actuating miniature metal or polymeric valves has been introduced. These valves might be actuated under the control of a sensor responding to a specific biological stimulus. This approach offers better reproducibility and easier control than drug release achieved by passive diffusion out of a polymer host matrix. The metal valve systems, which are irreversible, consist of thin suspended non-porous layers that can be electrochemically dissolved or disintegrated by water electrolysis. The reversible polymeric valve systems, also called ‘artificial muscle’, are prepared from a blend of redox polymer and hydrogel that swells and shrinks either by applying a suitable bias or through a specific chemical reaction. In one of the several possible configurations for the artificial muscle valves such as the sphincter configuration, the blend is electropolymerized within an array of holes, which open and close corresponding to the shrinking and swelling of the polymer actuator. The swelling and shrinking property of the blends is characterized by video monitoring and by in situ conductivity measurements. Significantly larger magnitude of swelling and shrinking were observed for the blend than the redox polymer itself. The blend also appeared smoother and more voluminous. The largest actuation was obtained for the blend consisting of polyaniline and poly(2-hydroxyethylmethacrylate)-poly(N-vinylpyrrolidinone). The results demonstrate that it is possible to apply artificial muscle for the fabrication of microactuator valves for responsive controlled drug delivery.