SCOTS engineers have developed a synthetic skin for prosthetic limbs that can generate its own energy from solar power – a development that could lead to amputees being able to “feel” an object and its temperature.

Researchers at Glasgow University had created an “electronic skin” made from graphene – a form of carbon made from flat sheets a million times thinner than paper – which was much more sensitive to touch, but needed a power source to operate its sensors.

This previously needed a battery, but the latest breakthrough has integrated photo-voltaic cells in to the skin material.

Dr Ravinder Dahiya, from the university’s School of Engineering, said: “The real challenge was how can we put skin on top of photo-voltaic and yet allow light to pass through the skin? That’s what we have done.”

The optical transparency of graphene, which is the world’s strongest material, allows around 98 per cent of the light that hits its surface to pass directly through it. This makes it perfect for gathering energy from the sun to generate its own power. Dahiya said human skin is an incredibly complex system capable of detecting pressure, temperature and texture through neural sensors which carry signals from it to the brain.

The researchers, whose paper is published in Advanced Functional Materials, had made significant steps in creating prototypes with synthetic skin that were capable of making very sensitive pressure measurements. This meant that prosthetic limbs could have a much a better sense of touch, temperature and texture.

“When the skin is placed on a prosthetic hand and the amputee then touches an object they are able to feel the contact pressure as well as temperature,” said Dahiya.

He added that the solar power capability meant there would be no need for an external battery to power the skin’s sensors.

“It is a skin that can generate its own energy, the power needed to operate it,” he said. “This from a prosthetic point of view leads to a skin that lets an amputee feel plus, without any additional battery, the prosthetic limb will be lighter.

“We are trying to bring the weight closer to the normal human hand. There is still a long way to go.”

The skin requires just 20 nanowatts (billionths of a watt) of power per square centimetre. Dahiya said the skin had generated more power than it needed but it was currently not possible to store the surplus. His team was already looking at ways to divert the unused energy into batteries, allowing it to be used when required.

“The other next step for us is to further develop the power-generation technology which underpins this research and use it to power the motors which drive the prosthetic hand itself,” said Dahiya.

“This could allow the creation of an entirely energy-autonomous prosthetic limb. We’ve already made some encouraging progress in this direction and we’re looking forward to presenting those results soon.”

The development could also help increase the functionality of robots, allowing them to have a better understanding of what they touch and interact with, added Dahiya.

If robots had touch and pressure-sensitive limbs, they would be less likely to make errors or injure humans, he said.

His team hopes to further develop the prototype in the next two years.