Prostheses are having a renaissance. Amputees with $10,000 or more can strap on a mechanical hand that they can actually control with their thoughts, much like they’re using a biological hand. But the hardware is heavy and robotic-looking, filled with tiny motors and hinges out of The Terminator.
Meanwhile, a new, milky-white prosthesis—developed by researchers at the Massachusetts Institute of Technology and Shanghai Jiao Tong University—moves with a soft, organic grace, as if it’s straight out of Westworld’s opening credits. Your eyes aren’t deceiving you; it truly is a breakthrough, especially since it costs a mere $500 to build. And for the more than 5 million people around the world who are upper limb amputees, that means the price of a brand-new hand could soon be on par with a new iPhone. (Except unlike an iPhone, you could run this hand over with your car and it would still work.)
How is this possible? As MIT professor Xuanhe Zhao, who led the research, explains, these are the sorts of benefits we can get from the field of soft robotics. Unlike most robots—which are built from hard metals and plastics, laced with complicated mechanics and electronics—soft robots are made of flexible, spongy, and elastomeric components. These materials are a lot more in line with the way our skin, muscles, and tendons work than hard titanium, which makes them perfect for rebuilding a human hand that’s flexible, strong, and soft to the touch.
MIT’s prosthetic is made largely from silicon rubber that’s reinforced by a carbon fiber skeleton, in a design that closely resembles real human anatomy. The hand moves through pneumatics—basically, air inflates and deflates each finger like a complex balloon animal—which cuts down on weight, mechanical complexity, and the sheer bulk of filling a hand with motors.
This softer hand has a softer touch. “With existing prosthetic hands . . . there’s always a risk of damaging something especially fragile, like a glass of water,” says Zhao, who notes that the hand isn’t just less likely to break things but also to break itself. This beefed-up rubber glove is nearly indestructible.
To keep the hand light, a small waistband holds the air pump system. As a result, this soft hand is actually a few grams lighter than a real human hand . . . whereas a mechanical hand can weigh nearly a pound, making it uncomfortable to wear for very long. It’s easy to activate the pump. All you have to do is think about moving your hand, and your arm muscles will fire electronic impulses. The hardware senses the impulses, turning on the pump, and your hand takes the proper shape.
This magic is thanks to the fact that sensors can now measure the electrical impulses in your arm muscles through electromyography, or EMG. While mind-controlled limbs might still seem like the stuff of sci-fi, Zhao says this part of the prosthetic device uses well-established technology. After slipping the hand on, software automatically prompts the user to think of a few specific gestures—like pinching at something small like a flower petal, or grasping something larger like a soda can. Because most people have very similar EMG readings for these types of tasks, the hand can actually read the user’s mind. So in less than two minutes, the hand syncs up with the body’s own wiring to recognize five common hand motions. To move the hand, the user just has to think about moving it.
On the fingertips, tactile sensors allow a wearer to know if the hand is touching something. (It’s not possible for people to actually feel these robotic fingers, but a patch placed on one’s upper arm vibrates to signal touch.)
Perhaps none of these individual innovations sounds all that impressive on its own, but when put together they add up to a prosthetic hand that works and feels a lot like a real human hand. You can use it to grab something as thin and fragile as a potato chip, or grasp another hand in a firm-but-safe handshake. By design, this rubbery, air-filled hand is naturally compliant.
As for next steps, Zhao would like to increase the speed of the pneumatic motions (you can see a slight delay in the video, where the wearer waits for his hand to catch up with his thoughts) and enable more variety of hand motions. Then, he’d like to either start his own business to produce these prostheses, or license the technology for other companies to use.
“Our eventual goal is to benefit millions of upper limb amputees,” says Zhao, noting that the hand’s $500 build price could democratize the technology for much of the world, assuming a private company doesn’t stack too much profit on top.
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