MILLIONS of diabetes sufferers could be spared painful injections after scientists invented a smart patch which monitors glucose levels and delivers insulin automatically.

The patch is a thin square no bigger than a postage stamp and sticks to the skin like a plaster. It can detect even slight increases in blood sugar levels meaning tiny doses of insulin can be given when needed.

It is covered with more than a hundred tiny needles, each about the size of an eyelash and packed with insulin and enzymes sensitive to glucose, in microscopic bubbles. When the enzymes detect raised blood-sugar, they release insulin.

Although it has only been tested on mice, its developers at the University of North Carolina say it could be a “game changer”.

“The whole system can be personalised to account for a diabetic’s weight and sensitivity to insulin,” said Prof Zhen Gu, of the department of biomedical engineering.

Diabetes, which can lead to blindness and loss of limbs, is thought to affect nearly four million people in Britain. Patients with type 1 and advanced type 2 diabetes currently have to regularly prick their fingers to monitor blood sugar and undergo repeated insulin injections.

“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 Dr John Buse, director of the University of North Carolina diabetes care centre.

“If we can get these patches to work in people, it will be a game changer.”

The research is published in the journal Proceeding of the National Academy of Sciences.