EVERY DAY, ABOUT 21 MILLION AMERICANS WITH DIABETES carefully negotiate their bodies’ inability to generate enough natural insulin, the hormone that helps the body process sugar.  Many inject insulin themselves, but getting the level just right can be delicate—too little insulin results in hyperglycemia, which can cause blindness, lost limbs or kidney failure, and too much insulin causes hypoglycemia, which carries the risk of seizure, brain damage or death. Another option is to transplant healthy beta cells—the insulin-producing units of the pancreas, which don’t function properly in diabetics—but they are often rejected by the immune system.

A research team from the University of North Carolina at Chapel Hill and North Carolina State University has devised another way to keep the balance—a quarter-size “smart patch” that safely harbors healthy, new beta cells on the surface of the skin, beyond the immune system’s reach. The patch, engineered from hyaluronic acid, a substance that occurs naturally in human tissue, is embedded with hundreds of micro-needles, each about the size of an eyelash (shown magnified behind this text). These are then packed with thousands of live beta cells as well as the nutrients necessary for cell growth.  When placed on the skin, the micro-needle patch penetrates small capillaries and blood vessels. The needles form a kind of highway that runs from the beta cells in the patch to the internal tissues where they’re needed. Like the naturally occurring beta cells found in the pancreas, these external cells sense the fluctuations in blood sugar that occur throughout the day and secrete insulin in response, which then diffuses down the micro-needle highway into the body.

So far, the patch has been tested only on mice. The smart patch quickly curbed runaway blood glucose, maintained healthy levels for up to 10 hours, and showed no risk of causing dangerously low blood sugar by releasing too much insulin. Indeed, instead of inducing hypoglycemia, a second patch was shown to balance glucose for an additional 10 hours. The results were published this past March in Advanced Materials. While more trials are needed before the patch can be tried on humans, the researchers believe that these patches, populated with beta cells derived from pig tissue or human stem cells, could bring a safer future for those with diabetes.