Stanford and Berkeley teams create ‘electric skin’

For an amputee, the body may continue feeling a phantom limb for long after the original is gone. Every arm or leg movement can carry the imaginary weight of a lost appendage, regardless of the presence of a prosthetic.

Yesterday, researchers from two groups in California published discoveries in the journal Nature Materials that should be well received by those with prosthetics. The two teams have each separately made significant advances in the ability to mimic human skin. Appropriately, the materials are being called “electric skin.”

The thin, flexible pressure sensing surfaces both have similar aims, yet use quite distinct approaches. Zhenan Bao, an associate professor of chemistry at Stanford University, and her team used organic electronics – with an elastic polymer called polydimethylsiloxane (PDMS) – to make their electric skin 1,000 times more sensitive than human skin.

From Nature News:

“Bao took a piece of PDMS measuring six centimetres square with pyramid-shaped chunks cut out of it at regular intervals. When the PDMS is squashed, the pyramid-shaped holes that were previously filled with air become filled with PDMS, changing the device’s capacitance, or its ability to hold an electric charge.

To make it easier to detect the changes in capacitance, Bao stuck the PDMS capacitor onto an organic transistor, which can read out the differences as a change in current. The team used a grid of transistors to track pressure changes at different points across the material. “

The faux-skin is so sensitive that Bao and her team tested it by putting insects on it; including a butterfly and an actual fly. While the current material isn’t stretchy enough to be used as a replacement skin for animals, the team hopes to have a prototype that can be incorporated into prosthetics by the end of the year.

The second team was based across the San Francisco Bay at UC Berkeley and used nanowire semiconductors that create a sensitive and flexible skin which can be draped over a conductive rubber with implanted transistors. The device then senses touch when something compresses the rubber and changes its electrical resistance, using very little power in the process.

Also from Nature News:

“In the 7-centimetre-square grid, the criss-crossing nanowires act as transistors. Each transistor is like a pixel, and the pressure-induced current change at each individual position can be read out. And because it’s made mainly of rubber, the device is bendy. “Because we’re using very small inorganic semiconductors, the devices are very flexible,” explains Javey. He has bent the sensor into a U-shape with each arm of the ‘U’ separated by a gap of just 5 millimetres and it still works.”

Interestingly, the Berkeley team mentions their prosthetic skin not only has applications for biomedical devices, but also applies to the interactions of artificial intelligence and humans (Data’s artificial skin in First Contact anyone?). They also mention that while such technology has been explored before, it has yet to be created in a cost-effective and sufficiently sensitive way.

Abstract/paper for UC Berkeley team’s research here

Abstract/paper for Stanford team’s research here

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