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Anew way of harnessing the sun's rays to power ‘synthetic skin’ could help to create advanced prosthetic limbs capable of returning the sense of touch to amputees. Engineers from the University of Glasgow, who have previously developed an ‘electronic skin’ covering for prosthetic hands made from graphene, have found a way to use some of graphene's remarkable physical properties to use energy from the sun to power the skin.

Dr. Ravinder Dahiya with the “synthetic” skin for prosthetic hands. (Credit: University of Glasgow)

Graphene is a highly flexible form of graphite that, despite being just a single atom thick, is stronger than steel, and it is electrically conductive and transparent. It is graphene's optical transparency, which allows around 98 percent of the light that strikes its surface to pass directly through it, that makes it ideal for gathering energy from the sun to generate power.

A new research paper, published in the journal Advanced Functional Materials, describes how Dr. Ravinder Dahiya and colleagues from his Bendable Electronics and Sensing Technologies (BEST) group have integrated power-generating photovoltaic cells into their electronic skin for the first time.

Dr. Dahiya, from the University of Glasgow's School of Engineering, says, “Human skin is an incredibly complex system capable of detecting pressure, temperature, and texture through an array of neural sensors which carry signals from the skin to the brain.

“My colleagues and I have already made significant steps in creating prosthetic prototypes which integrate synthetic skin and are capable of making very sensitive pressure measurements. Those measurements mean the prosthetic hand is capable of performing challenging tasks like properly gripping soft materials, which other pros-thetics can struggle with. We are also using innovative 3D printing strategies to build more affordable sensitive prosthetic limbs, including the formation of a very active student club called Helping Hands.

Schematic illustration showing the fabrication steps of graphene-based flexible capacitive touch sensors. A) Hot lamination transfer printing of CVD graphene on PVC flexible substrate. B) Graphene-on-PVC sample after etching the seed metal, i.e., Cu. C) Au deposition via e-beam evaporation through shadow mask. D) Patterning of graphene channel with an electronic cutting tool. E) Flexible capacitive touch sensor after spin-coating and curing of PDMS protective layer. F) Resultant graphene-based capacitive touch sensor. (Credit: Advanced Functional Materials, Wiley)

“Skin capable of touch sensitivity also opens the possibility of creating robots capable of making better decisions about human safety. A robot working on a construction line, for example, is much less likely to accidentally injure a human if it can feel that a person has unexpectedly entered their area of movement and stop before an injury can occur.”

The new skin requires just 20 nW of power per square centimeter, which is easily met even by the poorest-quality photovoltaic cells currently available on the market. And although currently energy generated by the skin's photovoltaic cells cannot be stored, the team is already looking into ways to divert unused energy into batteries, allowing the energy to be used as and when it is required.

Dr. Dahiya adds that another next step is to further develop the power-generation technology that underpins this research. He says they need to develop it to power the motors that drive the prosthetic hand itself, which 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. We are also exploring the possibility of building on these exciting results to develop wearable systems for affordable healthcare. In this direction, recently we also got small funds from Scottish Funding Council.”

The team's paper is titled “Energy Autonomous Flexible and Transparent Tactile Skin.” The research was funded by the Engineering and Physical Sciences Research Council (EPSRC).