Closed-loop glucose-responsive insulin delivery with excellent biocompatibility has the potential to improve the health and quality of life of diabetic patients. Herein, we developed an excellent glucose-responsive insulin delivery system using a pH-sensitive peptide hydrogel loaded with insulin and a glucose-specific enzyme. The designed peptide can be used as a carrier that is loaded with insulin and enzyme via a self-assembly process under physiological conditions. When hyperglycemia is encountered, the enzymatic conversion of glucose into gluconic acid leads to a decrease in the local pH, and the hydrogel is disassembled because of the strong inter- and intramolecular electrostatic repulsions between ornithine (Orn) residues; this is followed by the release of insulin. The glucose-responsive hydrogel system was characterized by studying its structure, conformation, rheology, morphology, acid sensitivity and the amounts of consistent release of insulin in vitro and in vivo. In vivo experiments indicated that the closed-loop insulin glucose-responsive system could efficiently regulate blood glucose in streptozocin-induced (STZ-induced) type 1 diabetic rats for 8 days.
Aglucose-sensitive polymer, poly(N-isopropylacrylamide-co-2acrylamidophenylboronic acid) (P(NIPAM-co-2-AAPBA)), was synthesized by RAFT copolymerization. Addition of glucose results in reduced solubility and hence increased turbidity, rather than the normal increase in solubility (decreased turbidity) observed for other PBA-based glucose-sensitive polymers. The novel glucose-sensitive behavior is explained by a new mechanism, in which glucose acts as an additive and depresses the lower critical solution temperature (LCST) of the polymer, instead of increasing solubility by increasing the degree of ionization of the PBA groups. Experimental and theoretic analysis for the influence of glucose on the thermal behavior of P(NIPAM-co-2-AAPBA) reveals that glucose depresses the LCST of P(NIPAM-co-2-AAPBA) copolymers in a two-stage manner, a fast decrease at low glucose concentrations followed by a slow decrease at high glucose concentrations. For low glucose concentrations, the binding of glucose with PBA groups on the polymer chain increases the number of glucose molecules proximal to the polymer which influences the thermal behavior of the polymer, causing a rapid decrease in LCST. Importantly, the transition occurs at a glucose concentration equal to the reciprocal of the binding constant between PBA and glucose, thus providing a novel method to determine the binding constant. Other saccharides, including mannose, galactose and fructose, also depresses the LCST of P(NIPAM-co-2-AAPBA) copolymer in the same way.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.