For all the advances we’ve made in prostheses in recent years—from artificial legs that closely mimic a natural gait to lifelike prosthetic arms that can twist and grip on command—they’re still largely one-way devices. Wearers can command their limbs to do something, but they receive little to no feedback in return. Picking up a cherry may be simple. Not crushing it in the process? Well, that’s a little more difficult.
Researchers may be on the cusp of changing that, though. Scientists and engineers at the Cleveland Veterans Affairs Medical Center and Case Western Reserve University have developed a prosthetic hand that returns a sense of touch via 20 sensors that are tied into the wearer’s nervous system.
David Talbot, reporting for Technology Review:
At the heart of the technology is a custom version of an interface known as a cuff electrode. Three nerve bundles in the arm—radial, median, and ulnar—are held in the seven-millimeter cuffs, which gently flatten them, putting the normally round bundles in a more rectangular configuration to maximize surface area.
Then a total of 20 electrodes on the three cuffs deliver electrical signals to nerve fibers called axons from outside a protective sheath of living cells that surround those nerve fibers. This approach differs from other experimental technologies, which penetrate the sheath in order to directly touch the axons. These sheath-penetrating interfaces are thought to offer higher resolution, at least initially, but with a potentially higher risk of signal degradation or nerve damage over the long term. And so they have not been tested for longer than a few weeks.
While there have been other prosthetic hands that provide feedback to the user through neural interfaces, the large number of touch-sensitive points appears to be a first. Researchers have been testing the new hand with a local former factory worker, Igor Spetic, who had his hand amputated after it was crushed in a drop forge. In tests seen in a YouTube video, you can see Spetic struggle to pluck a cherry from its stem. With an older prosthesis, he crushes fruit after fruit. But with the newer, sensor-laden device, Spetic nails the task nearly every time.
Spetic still hasn’t worn the device outside of the lab, but results appear promising, especially given how long he’s had the cuff electrodes embedded in his arm. We’re not quite ready to start doling out Luke Skywalker-like prosthetic hands, but we’re not far off, either.