Losing a limb is probably one of the most physically challenging things a person can face, which is one of the reasons why researchers have been working for decades to develope prosthetics with increasingly more advanced and “life-like” movements and capabilities.

A team at the University of Utah has contributed to this aim with the development of technology for a next-generation prosthetic arm that can “feel” and make movements according to the thoughts of the person wearing it.

The prosthetic--dubbed the “LUKE arm” after the one the character Luke Skywalker is fitted with in the film “The Empire Strikes Back”—can mimic the way a human hand feels objects by sending the appropriate signals to the brain.

This gives the person wearing it a sense of touch that allows him or her to pick up even delicate objects like eggs with a confidence rarely found in other modern prosthetics, said Gregory Clark, a University of Utah biomedical engineering associate professor who led the research.

“We changed the way we are sending that information to the brain so that it matches the human body. And by matching the human body, we were able to see improved benefits,” he said in a press statement. “We’re making more biologically realistic signals.”

Researchers have been working on the LUKE arm—comprised of metal motors and a clear silicon skin-like coating—for about 15 years. DEKA Research & Development Corp., a New Hampshire-based company founded by Segway inventor Dean Kamen, produced the computer-controlled prosthetic, which is powered by an external battery.

What the team at the University of Utah has specifically developed for the arm is a system that allows the device to tap into the wearer’s nerves, which act as biological wires that send signals to the arm to move.

Making the Nerve-Prosthetic Connection

The technology that enables this connection is an invention called the Utah Slanted Electrode Array developed by Richard Normann, a biomedical engineering emeritus distinguished professor at the university. The technology is a cluster of 100 microelectrodes and wires implanted into the nerves of a wearer’s forearm and connected to a computer outside the body.

What the array does is interpret signals from the arm nerves that still remain, while the computer turns them into digital signals that tell the arms to move, researchers said.  

The technology also works in another way, with the prosthetic arm learning how to “feel” an object it touches or picks up so it can intelligently apply the correct amount of pressure, they said. To do this, the prosthetic has sensors in its hand that send signals to the nerves via the array to mimic the feeling the hand gets when it grabs something.

However, how the signals are sent is just as important as that feeling, Clark said. “Just providing sensation is a big deal, but the way you send that information is also critically important, and if you make it more biologically realistic, the brain will understand it better and the performance of this sensation will also be better,” he said in the statement.

Researchers achieved a human-like way for this interaction by creating an approximate model for how the human body receives different signal patterns, Clark said. They used mathematical calculations along with recorded impulses from a primate’s arm to create this model, which was implemented into the LUKE Arm.

The team published a paper on its work in the journal Science Robotics.

Test Success

Researchers tested the technology they developed for the LUKE Arm on Keven Walgamott, who lost his hand and part of his arm in an accident 17 years ago. Walgamott said he could actually handle grapes and an egg dexterously thanks to the feeling in his arm, as well as hold his wife’s hand with a sensation in his fingers.

Clark and his team plan to continue their work to create a version of the technology that’s portable and doesn’t need to be wired to a computer, giving someone using the arm more freedom.

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They also want to expand on capabilities for the Utah Slanted Electrode Array to provide sensations beyond touch to expand to pain and temperature, researchers said. And by next year or 2021, Clark hopes that three test subjects can take the arm home to wear and use, if federal regulators approve the technology, he said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.