Glucose-Responsive Microspheres as a Smart Drug Delivery System for Controlled Release of Insulin

Diabetes mellitus, a disease of glucose regulation, has become one of the most common medical problems in the world. At present, alternative therapy for diabetes has, to a large extent, been widely concerned with the improvement of treatment efficacy. The aims of this study were to characterize and evaluate the surface morphology of the novel glucose-responsive injectable microspheres containing insulin, along with their in vitro release and in vivo efficacy. In this study, glucose-responsive microspheres as an emerging smart drug delivery system for controlled release of insulin were developed by an improved water-in-oil-in-water (W/O/W) double emulsion preparation method. Here, methoxypolyethylene glycol-hydrazone-4-methoxypolyethylene glycol benzoate (mPEG-Hz-mPEG4AB) was synthesized as a pH-responsive carrier. The microspheres had a good spherical structure with a particle size of 5 ~ 10 μm. Approximately 61% of insulin was released in 15 h under a high glucose environment but was barely released within the normal glucose range in in vitro studies. After a subcutaneous injection of insulin microspheres in rats, blood glucose levels rapidly decreased within 2 h and could be maintained for 2 days in the normal range. Histopathological evaluation indicated that the microspheres were almost non-irritating. The pH-responsive mPEG-Hz-mPEG4AB could be used as an efficient insulin microsphere carrier, and the optimized microspheres had good morphology and sustained hypoglycemic effect.