There could be hope for diabetics who are tired of giving themselves insulin injections on a daily basis. Researchers at North Carolina State University and the University of North Carolina at Chapel Hill are developing a system in which a single injection of nanoparticles could deliver insulin internally for days at a time – with a little help from pulses of ultrasound.

The biocompatible and biodegradable nanoparticles are made of poly(lactic-co-glycolic acid), and contain a payload of insulin. Each particle has either a positively-charged chitosan coating, or a negatively-charged alginate coating. When the two types of particles are mixed together, these oppositely-charged coatings cause them to be drawn to each other by electrostatic force.

This holds true even when they're injected into the subcutaneous layer of the skin, where they all join together to form what's described as a "nano-network." Since the nanoparticles are porous, the insulin begins to seep out of them once they're in the body. The electrostatic force still keeps the insulin close, however, causing it to form into a reservoir adjacent to the network.

When it's time to get a dose of that insulin into the bloodstream, a hand-held device is used to externally deliver focused waves of ultrasound to the nano-network. The scientists believe that this excites microscopic gas bubbles in the body tissue, disrupting the network and thus slackening the electrostatic force that ordinarily keeps the insulin reservoir from dispersing. In any case, the insulin is indeed able to enter the bloodstream, and is pushed along by the force of the ultrasound waves.

Once the ultrasound is turned off, the nano-network re-forms and more insulin leaks out to form another reservoir. In tests on diabetic lab mice, one injection of the nanoparticles was enough to regulate blood glucose levels for as much as 10 days. When a nano-network is depleted, another batch of particles can be injected – the old network will be absorbed by the body within a few weeks.

The scientists are now working towards applying the technology to humans. Dr. Zhen Gu is leading the research, which was recently described in a paper published in the journal Advanced Healthcare Materials.