ARI SHAPIRO, HOST:
Now a look at one of the great beneficiaries of technology - the human body. It's All Tech Considered.
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SHAPIRO: Artificial limbs have come a long way since the days of peg legs and hooks for hands. But one thing most prosthetics lack is a sense of touch. As part of his series Joe's Big Idea, NPR's Joe Palca introduces us to a chemical engineer who's trying to make an artificial skin that behaves very much like the real thing.
JOE PALCA, BYLINE: Skin is pretty remarkable stuff - it keeps dangerous bacteria and germs out and our innards in, it's flexible, it can sense when we touch things, and it can heal itself when cut. So Zhenan Bao has to make a pretty remarkable material if she's going to mimic all that - and she's getting there.
ZHENAN BAO: This is where we make some of the devices.
PALCA: We're in a shiny new lab in a shiny new building on the campus of Stanford University. The lab is part of the Shriram Center for Bio and Chemical Engineering. The devices Bao is making will ultimately be combined to form the artificial skin. We're standing next to a large sealed chamber with a clear window. There are long black gloves sticking straight out from the bottom of the box as if there were someone inside trying to reach out. It's just the air pressure in the box. You reach into the box with these gloves.
BAO: This is a nitrogen box.
PALCA: This is where new devices are tested before they're exposed to the air. Zhenan Bao builds her devices with a plastic she's specially designed that mimics the electrical properties of silicon, the element semiconductor chips are made from. Bao takes a small, clear square of plastic from a container on her desk. It's about the thickness of a piece of skin, and it contains a nanoscale pressure sensor.
BAO: These are some examples of this type of sensor.
PALCA: You can't really see it, but there's a pressure sensor sandwiched inside the layers of plastic. It changes its electrical properties depending on how hard you press on it. But it's not enough to just make a plastic with a built-in pressure sensor. You need to build an electrical circuit into the plastic that can relay what the pressure sensor is sensing. Zhenan Bao shows me they've done that.
BAO: So you can see there are some really fine lines, and these are electrodes that can turn the touch signal into electrical pulses.
PALCA: Ultimately, the idea is to feed those electrical impulses to nerve bundles that can transmit them to the brain. Now as I said, skin has the nice property that if you scratch it, it will heal. So to mimic that, Zhenan Bao and her colleagues have made a plastic that can actually repair itself if it's torn.
BAO: Depends on how we design the molecules. Some can repair very quickly, within a minute. Some take hours or days to recover.
PALCA: Making a flexible, stretchable plastic was also a problem at first.
BAO: But now we also have a new version that can stretch to eight times its original length.
PALCA: Zhenan Bao and her colleagues are working to crack another problem - how to power their artificial skin. One idea is to use light. Postdoc Xiaodan Gu shows me a polymer that can turn light into electricity.
XIAODAN GU: Those shiny things are electrodes. And on the top side - so you can see these tinted color are the active material. They absorb light and transfer the light into the electricity.
PALCA: Xiaodan Gu hopes to be able to use a version of his polymer to manufacture cheaper solar panels. And Zhenan Bao says there'll be other spinoffs as her lab works to build plastics with a variety of electrical properties. But those aren't the ultimate prize.
BAO: Our really long-term goal is to use this to help patient who lost their limb to recover their sense of touch.
PALCA: From the looks of things, she's well on her way. Joe Palca, NPR News.
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