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Designing a Smart Skin That Lets Amputees Feel Again

Author Nicholas Derenzo Illustration Jameson Simpson

howitsdone

Mind-controlled prosthetics may seem like something out of science fiction, but they’ve recently become a groundbreaking, game-changing reality. While bionic hands have allowed amputees to, say, play chess or hold a cup of tea, they haven’t managed to clear one major hurdle: restoring the sense of touch. But last December, Dae-Hyeong Kim, of the School of Chemical and Biological Engineering at Seoul National University, and his colleagues unveiled a new “smart” artificial skin for prosthetics in the journal Nature Communications. Equipped with integrated heating elements that emit warmth like a real hand (and thus keep it from feeling like a cold slab of rubber), the ultra-flexible, ultra-sensitive material is composed of hundreds of microscopic sensors that will eventually allow the user to “feel” temperature, moisture and pressure. Here’s how it will work.

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1. The synthetic skin is made up of a complex web of ultrathin silicon and gold ribbons embedded in stretchy transparent silicone rubber. The ribbons act as sensors and are arranged in wavy, serpentine patterns that allow it to stretch and bend to better mimic the elasticity of real human skin. In parts of the hand that require more flexibility, like the wrist, the ribbons are arranged in a looser pattern, while areas that require more sensation, like the fingertips, are densely packed with sensors.

2. In addition to detecting temperature, the sensors generate electricity when physically manipulated—poked, prodded, caressed, smooshed—registering stimuli like real nerve endings. They also include humidity sensors in the form of capacitors. When met with moisture, the capacitors’ ability to store a charge changes, and this shift is registered as a quantifiable measure of wetness. (Scientists tested this feature by having the hand touch wet and dry diapers.)

3. The final step involves figuring out exactly how to link the skin to the nervous system. In early tests on rats, researchers showed that when pressure was applied to the skin, an electric signal could successfully be sent to the brain via electrodes, though they can’t be sure precisely which sensations the rats experienced. Next up: much larger test subjects.

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