The Body Electric
Scientists want to develop electronic skin that could imbue prosthetics with the sense of touch.
Chao Wang didn’t always work on artificial skin. When he came to Stanford to work in the electronics lab, his background was in chemistry, specifically in making polymers. One day, he burned his hand in the kitchen, not badly, but enough to take a few days to heal. “After several days my skin came back,” he said, “and I started wondering if we could bring this self-healing back into our electronics.”
Wang now works on developing polymers that could regrow themselves and be used as artificial skin, an idea he says “seemed crazy” when he began. In 2012, he was part of a team that published a paper on self-healing plastic skin in Nature Nanotechnology. The research involved was a big deal not just because it showed that plastic could regrow itself—that work was already relatively well understood. It was a big deal because it combined self-healing properties with a structure that allowed the electrical connections to heal, too. In other words, the skin not only re-healed, it was also able to pass electrical signals from one end to another—so it wasn’t just physically repaired, but it still worked too. Since then, Wang has been steadily improving the artificial skin.
Once researchers proved it was possible to regrow a small patch of artificial skin, Wang says it would be relatively easy to scale the material up, building bigger sheets of the self-healing membrane. But there’s still one major hurdle before Wang feels like he’s really made artificial skin: stretchiness. “Our human skin can stretch up to 50 percent of its original length,” he told me. “That’s really important. If you want to cover robotics, it’s important, because on the joint and [other] areas, this motion will cause stretching.”
Wang’s tenure as a post-doc at Stanford is about to end, but he’s already lined up a job at the University of California in Riverside. There, he plans to continue working on building artificial skin that could be used for all kinds of applications. Wang might even create his own startup, to develop the technologies outside his lab, adding things like energy-storage capacity to the skin.
The obvious use for skin like this is on robots—one of the biggest complaints about things like prosthetic arms and legs is that users can’t feel anything with them. A farmer once told me that he accidentally welded his arm to the side of his tractor because he couldn’t feel it. Covering a prosthetic hand with artificial skin—skin that could feed into a neural interface—could bring touch back to those who’ve lost it.
But that’s a huge hurdle, says Dae-Heyong Kim, a professor of engineering at Seoul National University. “Reliably interfacing the prosthetic skin to nerve system is still the biggest challenge in making it for clinical uses.” His team worked on artificial skin that could deliver signals to the nerves of a rat, but he says making that technology work for humans—to be used with prosthetics, for example—is really difficult. “[The] human nervous system is much more complicated,” he said.
Kim’s team is working on patches of artificial skin that can help deliver drugs to patients. Last year, his team published a paper describing a small patch made of nanomaterials that released drugs based on the temperature of the skin beneath the patch. The idea is that should the skin heat up, or behave a certain way (tremors in a patient with Parkinson’s, for example), the patch could detect that and deliver drugs, stopping when the behavior is over.
Right now, though, these artificial skins are strictly for use in electronics. Building something that can replace a chunk of skin directly on your arm is a far more difficult proposition, including an almost impossible list of demands: To make artificial skin that could be grafted onto a human body it would have to be thinner, more sensitive, permeable to air and water, stretchable, tearable, repairable, and somehow still have a built-in energy source to power the whole thing. Until electric skin is a reality, patients with large segments of skin tissue missing have a whole slew of other options: If skin can’t be replaced using tissue harvested from elsewhere on the body, for instance, doctors can use donated skin or synthetic skins made of things like nylon mesh, collagen, and silicone.
But eventually both Wang and Kim believe the merger of artificial and biological skin will happen. First, it’s likely people will put one on top of the other. “In the future, this electronic skin can be directly applied to your human skin and detect your heartbeat and pulse and other functions, just a simple example, like you have a smartwatch,” says Wang. He imagines that instead of a Fitbit, people might have a little square of second-skin that gathers data about their movements and health metrics.
Once researchers have figured out how to power and slim down the skin, and how to connect it to the neurons that already exist in a body, Kim says the artificial skin patch or implant could happen. But that will take time. “The skin is very very delicate,”said Wang. “It’s so beautiful and has so many functions. Our human skin is for protection, it’s permeable, we don’t think our skin can replace human skin at least for now.”