Graphene helps tactility of solar powered prosthetic skin

Synthetic skin powered by the sun could give the sense of touch to robots and amputees fitted with prosthetic limbs.

Dr Ravinder Dahiya
Dr Ravinder Dahiya

Researchers at Glasgow University have developed a new way of generating solar power for robotic and prosthetic limbs using graphene.

Graphene is an atom-thick layer of material, which includes high conductivity as one of its numerous properties. The researchers have previously used graphene to build a pressure-sensitive electronic skin for prosthetic hands.

Now, in a paper published in Advanced Functional Materials, they demonstrate that another of graphene’s properties – its optical transparency – can also be harnessed for electricity generation. Around 98 per cent of the light that hits the material’s surface passes straight through it, according to Dr Ravinder Dahiya.

So by placing solar cells directly underneath the layer of graphene, electricity can be generated to power the synthetic skin, he said.

“If we fabricate a solar cell and transfer the skin on top of that, then the entire structure will be able to generate power, because light can enter through the skin, and it will also be touch sensitive,” said Dahiya.

The skin, which needs 20nW of power per square centimetre, is capable of making very sensitive pressure measurements, allowing it to perform tasks such as judging the correct strength to grip soft materials.

Existing prosthetic limbs do not typically have this tactile feedback, so research groups around the world are attempting to develop synthetic skin, he said.

“If you were to put your hand into an ice block for a few seconds and then try to grab an object, very likely you wouldn’t be able to do it,” said Dahiya. “Without tactile feedback it is extremely difficult to grab or manipulate an object,”.

The technology could also allow industrial robots to feel when a person has entered their work area, and stop moving before they injure them.

Although energy generated by the skin’s photovoltaic cells cannot be stored at the moment, the team are investigating the possibility of adding a separate layer of graphene, to act as a supercapacitor. This could be placed underneath the solar cells, to store excess electricity for use when needed.

The graphene supercapacitor would be flexible, thin, and should be capable of storing enough charge to power both the touch-sensitive skin and the prosthetic limb’s motors, said Dahiya.

This could ultimately lead to a completely self-powered prosthetic.

What’s more, unlike a conventional battery, the supercapacitor would not add significant weight to the prosthetic, which can reduce an amputee’s sense that it is their “own” limb, said Dahiya.

“If you put a battery on a prosthetic limb, the amputee will never feel it is part of their own body, and ownership is important if you want to make it as close to a human hand as possible, for example.”