Scientists have developed a shoe insole that could help heal diabetic ulcers -- a condition that often leads patients to lose their toes, foot or leg.

Diabetes can lead to ulcers that patients do not feel or notice until the sight of blood. These ulcers can not heal on their own.

Researchers from Purdue University in the US have made the healing process more portable for those who develop ulcers as a result of diabetes.

"One of the ways to heal these wounds is by giving them oxygen," said Babak Ziaie, professor at Purdue.

"We've created a system that gradually releases oxygen throughout the day so that a patient can have more mobility," said Ziaie.

Diabetic ulcers commonly result from high blood sugar damaging nerves, which takes away feeling from the toes or feet.

Without the ability to feel pain, hits and bumps tend to go unnoticed and skin tissue breaks down, forming ulcers. A lot of sugar in the bloodstream, along with dried skin as a consequence of diabetes, further slow the ulcer healing process.

"We typically treat ulcers by removing devitalised tissue from the surface of the wound, and by helping the patient to find ways to take the weight off the affected foot," said Desmond Bell, from the Memorial Hospital the US.

"The gold standard for treating an ulcer is a patient wearing a total-contact cast, which provides a protective environment for the foot," said Bell.

"If we could test how well this insole delivers oxygen to the wound site from within the cast, then this could be a way of aiding the healing process," he said.

Researchers used lasers to shape silicone-based rubber into insoles, and then create reservoirs that release oxygen only at the part of the foot where the ulcer is located.

"Silicone is flexible and has good oxygen permeability," said Hongjie Jiang, a postdoctoral researcher at Purdue.

"Laser machining helps us to tune that permeability and target just the wound site, which is hypoxic, rather than poison the rest of the foot with too much oxygen," said Jiang.

According to the team's simulations, the insole can deliver oxygen at least eight hours a day under the pressure of someone weighing about 53-81 kilogrammes.

However, the insole can be customized to take on any weight, the researchers say.

The team envisions a manufacturer sending a patient a pack of pre-filled insoles customised to his or her wound site, based on a "wound profile" obtained from a doctor's prescription and a picture of the foot.

Next, the researchers want to create a way to 3D print the whole insole, rather than printing a mold first and then laser-machining a pattern.

They also plan to test the insole on actual diabetic ulcers, to further gauge how well they advance the healing process.