[Recent trends in drug delivery systems using biomaterials].

Since the concept of sustained release of biologically active agents was established in 1970's, the sustained release has been examined by controlling the diffusion of drugs through polymeric matrices and/or the degradation of these polymers. Recently, drug release in proportion to internal or external stimuli has been getting important, which can be achieved by using stimuli-responsive polymeric materials. Majority of these polymers have been designed as to achieve their functions by changes in temperature, pH, glucose concentration, and the release of ribosomal enzymes. Especially, among those materials, biodegradable polymers have much potential for applications as implantable carriers for drug delivery system (DDS). In an auto feed-back drug delivery, several physiological changes in a living body can be utilized as the signal inducing polymer degradation and subsequent drug release. A hydrogel composed of hydrophilic biomaterials has been focused because of their high responsibility to the stimulus. In this paper, currently investigated DDS using hydrogels are reviewed with their strategies.