Close your eyes and raise a hand.
You know you are performing this action because your body sent a signal to your brain about where your arm was in space, even though you didn’t see it happen. But for people who have had an arm, foot, or limb amputated, that sensory feedback does not occur ― the surgery severs the pathways that used to send those signals to the brain. Even with a high-tech prosthetic device, amputees can no longer experience the same type of sensation or have the ability to move as precisely as they once did.
Shriya Srinivasan, who earned a doctoral degree in biomedical engineering at the Massachusetts Institute of Technology and Harvard Medical School last year, is working to preserve an amputee’s natural sense of touch. The 26-year-old won the MIT $15,000 Cure it! Lemelson-MIT Student Prize last year for the idea, and earlier this month her research was published in a medical journal.
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“Usually when an amputation happens, a surgeon will cut off a nerve and leave it dangling,” she said. “Your body knows at all times where your arms and legs are, but for a person with an amputation, that sensation is lost.”
Srinivasan has devised a new way to perform amputation surgery that would reconnect dangling nerves to the skin. The method would be used to create an organ-like implant that can convey sensations, sending signals between the brain and a prosthetic device.
“The patient doesn’t have to learn a new sensation or new way of communication...it communicates through natural pathways,” she said. Srinivasan also created a way to perform the surgery on existing amputees.
Her method is based on a sister surgery called the AMI method, invented at the MIT Media Lab, which reconnects agonist and antagonist muscles in amputees. The AMI surgery is being tested in humans.
While there are several options for “active” prosthetic devices on the market, Srinivasan said, amputees sometimes abandon them because they don’t transmit information back to the brain.
“If you were going to pick up a cup with your prosthetic hand, you would have to look and confirm your hand is closed [around the cup] before you move it, and that is too frustrating” she said, likening it to “using a typewriter to type into the Internet.”
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Srinivasan said her procedure allows amputees to know the second they touch something that they have made contact with it ― without visual confirmation.
Srinivasan said she was inspired to help restore the sense of touch after growing up with a friend who was born without a right arm and a left leg. The two met during dance classes in Ohio, where Srinivasan was born and raised.
“As a dancer, your sense of where your limbs are in space is really key to being able to move smoothly,” she said. “Putting my science cap on, I realized not having that automatic sensory feedback to your body was a huge gap for the field.”
Her principal investigator on the amputation project is also an amputee, Srinivasan said. He told her that having a sense of where his prosthetic foot is on a floor would greatly improve his ability to maintain balance.
“We drew this [idea] out on a napkin at a conference, tried it on animals a couple months later, and started working on publishing the results by the end of [2019],” she said.
Srinivasan plans to begin a clinical trial for the surgical method by the end of the year at the Brigham and Women’s Hospital in Boston. She’s also having conversations with companies that make prostheses about licensing the technology so patients can choose from a variety of devices after surgery.
“I would hope that in the next 10 years, people are offered the ability to have these advanced techniques incorporated into their initial surgery,” she said. “Whether or not they have a prosthetic device when they recover, they have this functionality available, so as prostheses become available and accessible, they can plug into those features.”
Anissa Gardizy can be reached at anissa.gardizy@globe.com. Follow her on Twitter @anissagardizy8 and on Instagram @anissagardizy.journalism.