Even Smarter Prosthetics

Engineering artificial skin with a sense of touch

Adrianne Haslet-Davis was out on a date with her husband on Boston’s Boylston Street on April 15, 2013, when a bomb exploded. Three people were killed and 264 injured during the Boston Marathon bombing. She lost her left leg below the knee.

Yet the professional ballroom dancer was back on her feet within weeks using a prosthetic leg. She has continued to dance and win ballroom competitions, in addition to lobbying Congress to make prosthesis coverage mandatory for health insurance companies.

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“I love my prosthesis,” she said.

It allows her to run, walk, dance, but the lack of sensory input can be challenging.

“I train in different studios around Boston and, as winter approaches, I worry about not having a feel of the ground, given how icy it gets here,” she told LifeZette.

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Building a prosthesis that can identify sensations is still an uncrossed scientific frontier.

But last month, a team at Stanford University published a paper in Science that marked a step in that direction. Led by Stanford professor of chemical engineering Zhenan Bao, the group created a material that has circuits and sensors that can pave the way for an artificial skin with the ability to feel pressure.

Artificial limbs that can “feel” is still an uncrossed scientific frontier; Stanford researchers have taken a step in that direction.

“The work could have important implications for the development of smarter prosthetics,” said Ali Javey, a professor at the University of California, Berkeley.

It could improve the quality of life to the 1.9 million individuals in the U.S. who have lost limbs.

Bao, who has been working on the project for more than a decade, said that the electronic skin, or “e-skin,” as it’s known, “mimics how our skin reacts when pressure is sensed.”

“The signal processing happens at the fingertips and then sends signals to brain. It’s a lot like Morse code,” she said.

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Traditional approaches to creating artificial skin had wires connected to individual sensors, which limited how many could be built. This material is paper-thin, strong and flexible. It is made out of elastic synthetic rubber that is embedded with billions of tiny carbon nanotubes that are highly conductive to electricity. When compressed, pressed or squeezed, the nanotubes send electrical signals that convey information to the brain.

But while the pressure points can register the sensation, the trick was sending the information to the brain.

“Human skin is the best digital computer ever,” said Benjamin Tee, the study’s co-author and a scientist at the Institute of Materials Science and Engineering in Singapore. “What makes digital signals so efficient is that you can send many signals at once.”

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To reach the brain more effectively and cut out intervening “noise,” the team used optogenetics to convert the signals into high-frequency light waves and shone the light beam on a mouse brain. Parts of the brain were bioengineered to respond to light waves (normally, mammalian brains do not) and read the information.

Bao acknowledges they are still far away from building a skin that would allow the kind of prosthetics that Haslet-Davis uses to tell if she is stepping on ice or into mud. The next step is testing the artificial skin in live animals.

Sliman Bensmaia, a neurobiologist at the University of Chicago, agreed the study was a “step in the right direction.”

“Having touch is so important for restoring function for amputees — it’s even more important than vision,” Bensmaia said.

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