Glucose-Responsive Polymer Gel Bearing Phenylborate Derivative as a Glucose-Sensing Moiety Operating at the Physiological pH

The work attempts to prepare a totally synthetic, glucose-responsive polymer gel bearing a phenylborate derivative as a sensor moiety to glucose, for future use as a self-regulated insulin delivery system. The molecular strategies to enable the system to be operated under physiological conditions (pH 7.4, 37 degrees C) are presented that involve the use of a novel phenylborate derivative [4-(1,6-dioxo-2,5-diaza-7-oxamyl) phenylboronic acid: DDOPBA] possessing an appreciably low pK(a) ( approximately 7.8), the adoption of poly(N-isopropylmethacrylamide) (PNIPMAAm) for the main chain, which itself undergoes a sharp thermo-induced phase transition at its LCST around 40 degrees C, as well as the introduction of a carboxyl group of methacrylic acid as the third comonomer. Glucose-responsive behaviors of the obtained gels were evaluated based on the changes in the equilibrium swelling degree determined in the presence and the absence of glucose, for various pH and temperature conditions. As a consequence of the combined molecular effects, a sufficient sensitivity of the system was accomplished at physiological pH and in the temperature range close to the physiological condition such as 30 degrees C. Furthermore, the glucose-induced continuous volume changes of the gels were demonstrated under those conditions, which occurred in a remarkably concentration-dependent manner. In these experiments, the critical glucose concentrations to induce the gels' responses in the range of normoglycemic sugar level were observed. These observations may provide us with an excellent prospect for the use of the gel as a self-regulated, insulin-delivery system discretely switching the release at the normoglycemia.