Drug particle delivers insulin on demand.

Chemical engineers at the Massachusetts Institute of Technology have developed injectable polymer particles that can store and release insulin in the body in response to changes in blood-glucose concentrations.

The particles are crafted from the polymer dextran, a sugar-binding protein, and insulin. Mixed together, the materials self-assemble into tiny, insulin-loaded particles.

Put into a glucose solution, the particles partially dissolved, releasing some insulin. Coinvestigator Todd Zion attributes this to a competition between sugar molecules in dextran and the glucose in the solution to bind with the protein molecules. When the concentration of glucose in solution decreased, the particles stopped releasing insulin.

"Only the surface peels away with each cycle" of glucose exposure, says Zion. When injected under the skin, the particles are expected to store and release enough insulin for 2.5 days, the researchers say. Because the particles respond quickly to changes in glucose concentrations, diabetic people could presumably achieve fighter control over their blood sugar with the new particles than with multiple daily insulin injections.

Zion and his colleagues have successfully tested a version of the drug-release system in diabetic rats. The team has launched a company called SmartCells to commercialize the technology.--A.G.