Electro-responsive drug delivery from hydrogels.

Precise control over the release of drug from devices implanted in the body, such as quantity, timing, is highly desirable in order to optimise drug therapy. In this paper, the research on electrically-responsive drug delivery is reviewed. Electrically-controllable drug release from polyelectrolyte hydrogels has been demonstrated in vitro and in vivo (in rats). Pulsatile drug release profiles, in response to alternating application and removal of the electric field have been achieved. Responsive drug release from hydrogels results from the electro-induced changes in the gels, which may deswell, swell or erode in response to an electric field. The mechanisms of drug release include ejection of the drug from the gel as the fluid phase synereses out, drug diffusion along a concentration gradient, electrophoresis of charged drugs towards an oppositely charged electrode and liberation of the entrapped drug as the gel complex erodes. Electrically-responsive drug release is influenced by a number of factors such as the nature of the drug and of the gel, the experimental set-up, magnitude of the electric field etc. In this paper, electrically-responsive hydrogels, response of gels to an electric field and electrically-stimulated drug release are discussed.