Development of self-regulated insulin delivery system based on novel glucose-responsive gel

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Recently, polymeric gels which change their physicochemical properties with external stimuli have been the subject of great interest because of their potential utility as chemical valve system for controlled drug release, analytical and preparative separations, and sensor technologies. Indeed, remarkable progress has been made in the development of gels responding to physical stimuli such as heat and light. Yet, few examples are known of totally synthetic gels responding to chemical stimuli, i.e., a concentration change in particular molecules in the milieu, regardless of their wide applicability as described above. More specifically, development of sugar-responsive gels may give a great impetus to construct a self-regulating insulin-delivery system, mimicking the function of β-cells in pancreas, for the treatment of diabetes. In this research project, totally synthetic polymer gels responding to external glucose concentration was firstly prepared. The gel was composed of polymer strands showing lower critical solution temperature, such as poly (N-isopropylacrylamide) (PNIPAAm), with a small quantity of phenylboronic acid as glucose-sensing moieties. Repeated volume phase transition of the gel was demonstrated under microscopy equipped with a video monitor at isothermal condition with a change in glucose concentration due to the shift in the equilibrium of phenylboronic acid between the undissociated (or uncharged) and the dissociated (or charged) form through complexation with glucose. Further, on-off regulation of insulin release from the gel was achieved responding to a change in external glucose concentration, indicating a potential utility of this novel type of glyco-sensitive gel in self-regulated insulin delivery systems.