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A Deft Robotic Hand That’d Make Luke Skywalker Proud

In an ordinary lab at the University of Michigan, Joseph Hamilton, of Flint, does the also-ordinary: He grabs a shiny ball and a bottle; he presses buttons and stacks little cubes; he zips and unzips zippers. Well, it would be ordinary if Hamilton wasn’t an amputee doing this all with a robotic hand—à la Luke…

In an ordinary lab at the University of Michigan, Joseph Hamilton, of Flint, does the also-ordinary: He grabs a shiny ball and a bottle; he presses buttons and stacks little cubes; he zips and unzips zippers. Well, it would be ordinary if Hamilton wasn’t an amputee doing this all with a robotic hand—à la Luke Skywalker—and if he wasn’t a test subject for a major advance in the control of robotic limbs.

“It worked awesome,” Hamilton says of his test-run with the robotic hand. “If it was something that I had access to for daily use, it would make life so much easier.”

Up until this point, researchers have succeeded in giving amputees control over robotic hands by measuring nerve activity in the residual limb. That signal is extremely faint, resulting in clunky control of the prosthesis—the wearer may need to flex their shoulder to get the device’s thumb to move, for instance. But writing today in the journal Science Translational Medicine, researchers describe a clever way to amplify these signals for users like Hamilton. It’s so effective, participants can put on the robotic hand and pull off fine motor functions right away, no training required.

It all comes down to how the patients regrow their nerves. When a person loses, say, their arm from the elbow down, all their nerves want to grow back where they were before. “Patients get this big ball of nerves called a neuroma,” says University of Michigan plastic surgeon Paul Cederna, who co-developed this new system. “And that can lead to pain and can prevent them from wearing their prosthesis and severely impact their quality of life.”

Courtesy of University of Michigan Engineering

But the nerves’ proclivity for growth is also the trick with this new technique. Cederna and his colleagues took small pieces of muscle and surgically wrapped them around nerve endings in the residual limb. Instead of balling up, the nerves innervated the muscle tissue, which greatly amplified their electrical signal. Think of it like building a megaphone for nerves.

“So we were able with this approach to not only treat the end of the nerve to prevent the nerve from getting the neuroma pain and phantom pain,” Cederna says, “but also at the same time take those tiny little signals and amplify them with that piece of muscle.” They also added electrodes to the muscle to detect the signals, which were now up to 100 times more powerful than before the nerves grew into the muscle. By this point, the nerves were downright shouting. (By the way, a skin graft wouldn’t work as well as a muscle graft, because motor nerves don’t go to skin.)

In their experiments with Hamilton and three other subjects, the team found that after doing the grafts, the nerves that control the thumb interacted with this new muscle just as they would if the person still had their thumb. “We know the intent—in that case, to flex the thumb—just like the nerve and muscle interacted when there was a thumb,” says Cederna.

Courtesy of University of Michigan Engineering

Next, the team had the subjects simply imagine a bunch of different hand movements. As they did so, an EKG picked up the signals of their nerves activating, just as the nerves would have done before the person lost their limb. They tracked these to pair particular nerve signals with particular movements. “The anatomy is making these signals very different from one another, and is very finger-specific,” says University of Michigan biomedical engineer Cindy Chestek, who co-developed the system. One nerve might be highly active for controlling the thumb, for instance, but remain silent when another finger is moving.

All of this information is fed to algorithms, which lea

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