New soft 'e-skin' mimics human sense of touch, talks to brain

Researchers have developed a single, multilayer, soft and stretchable material with integrated nerve-like electronics that can sense pressure, temperature, strain, and more, just like real skin as well as talk to the brain.

Engineers eager to create artificial electronic skin have so far been able to fashion soft, flexible materials that mimic our remarkable senses, but so far they did not create a single sheet with skin-like materials that can directly talk to the brain.

While previous efforts required rigid electronics to convert the sensed signal into electrical pulses that the brain can read, researchers at Stanford University have produced soft integrated circuits that convert sensed pressure or temperature to electrical signals similar to the nerve impulses to communicate with the brain.

The researchers hope someday that those signals might be directed to implanted wireless communication chips in the peripheral nerve to allow amputees to control prosthetic limbs.

Other potential uses might include new-age implantable or wearable medical devices, they described in the study appearing in the journal Science.

"We've been working on a monolithic e-skin for some time. The hurdle was not so much finding mechanisms to mimic the remarkable sensory abilities of human touch, but bringing them together using only skin-like materials," said Zhenan Bao, Professor in Chemical Engineering at the varsity.

"This new e-skin runs on just 5 volts and can detect stimuli similar to real skin," said Weichen Wang, a doctoral candidate in Bao's lab.

The team invented a tri-layer dielectric structure that helped increase the mobility of electrical charge carriers by 30 times compared to single-layer dielectrics, allowing the circuits to operate at low voltage.

Interestingly, one of the layers in the tri-layer is nitrile, the same rubber that is used in surgical gloves. The majority of e-skin is made of many layers of skin-like materials.

Integrated in each layer are networks of organic nanostructures that transmit electrical signals even when stretched. These networks can be engineered to sense pressure, temperature, strain and chemicals.

Each sensory input has its own integrated circuit. Then all the various sensory layers must be sandwiched together into a single monolithic material that does not delaminate, tear, or lose electrical function.

Each electronic layer is just a few tens to hundred nanometers thick and the finished material of half a dozen or so layers is less than a micron.

"But that's actually too thin to be handled easily, so we use a substrate to support it, which brings our e-skin to about 25-50 microns thick - about the thickness of a sheet of paper," Bao said. "It is in a similar thickness range of the outer layer of human skin."

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