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‘Smart’ Insulin Patch Could Replace Injections for Diabetes

Insulin-filled nanoparticles may be ‘game changer,’ expert says

Insulin injections could become a thing of the past for the millions of Americans with diabetes, according to researchers at the University of North Carolina and North Carolina State, who have created a “smart insulin patch” that can detect increases in blood sugar levels and secrete doses of insulin into the bloodstream whenever needed.

The patch –– a thin square no larger than a penny –– is covered with more than 100 “microneedles,” each about the size of an eyelash. These tiny needles are packed with microscopic storage units for insulin and glucose-sensing enzymes, which rapidly release their cargo when blood sugar levels get too high.

In a study published in the Proceedings of the National Academy of Sciences, the researchers found that the new, painless patch could lower blood glucose in a mouse model of type-1 diabetes for up to 9 hours. More preclinical tests and subsequent clinical trials in humans will be required before the patch can be administered to patients.

“We have designed a patch for diabetes that works fast, is easy to use, and is made from nontoxic, biocompatible materials,” said co-senior author Zhen Gu, PhD. “The whole system can be personalized to account for a diabetic’s weight and sensitivity to insulin, so we could make the smart patch even smarter.”

Diabetes affects more than 387 million people worldwide, and that number is expected to grow to 592 million by the year 2035. Patients with type-1 and advanced type-2 diabetes try to keep their blood sugar levels under control with regular finger pricks and repeated insulin shots. Co-senior author John Buse, MD, PhD, said, “Injecting the wrong amount of medication can lead to significant complications, like blindness and limb amputations, or even more disastrous consequences, such as diabetic comas and death.”

In the past, researchers have tried to remove the potential for human error by creating “closed-loop systems” that directly connect the devices that track blood sugar and administer insulin. However, these approaches involve mechanical sensors and pumps, with needle-tipped catheters that have to be inserted under the skin and replaced every few days.

Instead of inventing another man-made system, Gu and his colleagues decided to minic the body’s natural insulin generators, known as beta cells. These versatile cells act as both factories and warehouses, making and storing insulin in tiny vesicles. They also behave like alarm call centers, sensing increases in blood sugar levels and signaling the release of insulin into the bloodstream.

“We constructed artificial vesicles to perform these same functions by using two materials that could easily be found in nature,” said first author Ji-ching Yu, a PhD student in Gu’s lab.

The first material was hyaluronic acid (HA), a natural substance that is an ingredient of many cosmetics. The second material was 2-nitroimidazole (NI), an organic compound commonly used in diagnostics. The researchers connected the two materials to create a new molecule, with one end that was hydrophilic and one that was hydrophobic. A mixture of these molecules self-assembled into a vesicle, much like the coalescing of oil droplets in water, with the hydrophobic ends pointing inward and the hydrophilic ends pointing outward.

The result was millions of bubble-like structures, each 100 times smaller than the width of a human hair. Into each of these vesicles, the researchers inserted a core of solid insulin and enzymes specially designed to sense glucose.

In laboratory experiments, when blood sugar levels increased, the excess glucose crowded into the artificial vesicles. The enzymes then converted the glucose into gluconic acid, consuming oxygen at the same time. The resulting hypoxia made the hydrophobic NI molecules turn hydrophilic, causing the vesicles to rapidly fall apart and send insulin into the bloodstream.

Once the researchers had designed these “intelligent” insulin nanoparticles, they had to figure out a way to administer them to patients with diabetes. Rather than rely on the needles or catheters that had beleaguered previous approaches, they decided to incorporate the tiny spheres of sugar-sensing, insulin-releasing material into microneedles.

Gu created the tiny needles using the same HA that was a chief ingredient of the nanoparticles, only in a more rigid form so that the tiny needles were stiff enough to pierce the skin. The investigators arranged more than 100 of these microneedles on a thin silicon strip to create what looked like a tiny, painless version of a bed of nails. When this patch was placed onto the skin, the microneedles penetrated the surface, tapping into the blood flowing through the capillaries.

“The hard part of diabetes care is not the insulin shots, or the blood-sugar checks, or the diet, but the fact that you have to do them all several times a day every day for the rest of your life,” said John Buse, MD, PhD, director of the North Carolina Translational and Clinical Sciences Institute. “If we can get these patches to work in people, it will be a game changer.”

Sources: Medical Xpress; June 22, 2015; and PNAS; June 22, 2015.

 

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