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Revolutionary Prosthetics

By Michelle Moncrieffe
Illustration of a prosthetic hand making the
Michael McLoughlin is the chief engineer of the Research and Exploratory Development Department at the Johns Hopkins University Applied Physics Laboratory, where he leads the Revolutionary Prosthetics program.

Two years ago, Melissa Loomis, age 43, was in her house in Ohio when she heard her two dogs barking and scuffling outside. She discovered her pets in a tussle with a raccoon, and she ran to intercede. The wild animal bit her right forearm. Weeks later, Loomis lost her limb above the elbow to a septic infection. At the suggestion of her surgeon, Loomis came to the Applied Physics Laboratory (APL) to test an exciting new breakthrough in prosthetics. Today she is one of the world’s first amputees to regain a sense of touch through a mind-controlled prosthetic robotic arm.

The design of this next generation modular prosthetic limb has been years in the making by engineers at APL, through a program funded by the U.S. Defense Advanced Research Projects Agency, known as DARPA. With 26 joints, the prosthesis can curl up to 45 pounds and matches the natural dexterity of a human arm. Coming in at just over 9 pounds, the prosthesis weighs little more than a human arm, and it’s designed to integrate with the body and use the brain’s natural neurotransmissions for control. It’s a major leap forward in the world of prosthetics, says Mike McLoughlin, chief engineer at APL, as amputees often contend with heavy, uncomfortable, and static replacements. “There were two challenges: to emulate the human arm and provide the control that is very natural,” McLoughlin says.

This iteration is the first to provide sensory feedback to the amputee. Loomis underwent a 16-hour surgery called targeted sensory reinnervation. It works by remapping the nerves onto new muscles in the arm. Several of these nerves send signals from the brain down to the hand, but when the limb is missing, those messages have nowhere to go (accounting for the phantom limb sensation many amputees experience). When surgically grafted onto a new location on the remaining upper arm, and then con­nected to a sensory cap designed for the prosthesis, the nerves that used to go to the hand are stimulated. Only instead of controlling a hand, the amputee is controlling the prosthesis. The simulation cap works by transmitting electric signals directly from the nerves to the prosthesis, reactivating those paths to the brain. Think Grab the ball, and the hand will grab the ball. “The power in this is that we don’t have to trick the brain, we use what was already there, so the brain doesn’t have to learn how to interpret signals from the prosthesis,” McLoughlin says.

When surgically grafted onto a new location on the remaining upper arm, and then connected to a sensory cap designed for the prosthesis, the nerves that used to go to the hand are stimulated. Only instead of controlling a hand, the amputee is controlling the prosthesis.

In early tests in April 2016, Loomis strapped the simulation cap onto her remaining arm with the remapped nerves, and using her mind to control the prosthesis, she picked up and dunked an orange ball in a basket. More important, though, she could feel the ball in the mechanical hand. Over 100 sensors in the arm sent messages back to her brain.

“You control your hand with your mind naturally, so to me I feel like I have a hand and I’m moving it naturally,” Loomis told Motherboard magazine on the day of the trial at APL. “It’s just incredible. I felt the orange ball.”

McLoughlin says that this development brings hope to people who have lost limbs through stroke, illness, and accidents, as well as to those born without complete limbs. It’s a “conduit to mobility,” he says, and would allow people not only to have the function of the arm but to feel the hand of a spouse, or the warning warmth of a hot surface. Researchers aim to make the next phase of this program noninvasive: Imagine no surgeries or implants—just placement of a sensory cap. To make this technology accessible to patients like Loomis, his team is focusing on continued innovation to drive down the cost.

Illustration of a woman with an arm composed of flowers reaching down to add a single bloom to a flower bed
Illustration above by Justin Renteria; Illustration to the left by Mitch Blunt
While prosthetic limbs have come a long way, amputees still cannot feel sensory sensations through their replacement. A revolutionary prosthesis from the Johns Hopkins University Applied Physics Lab promises to change that.

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