New Robotic Prosthetic Arm Enables Amputee to Sense Touch

Keven Walgamott felt positive about grasping the egg without crushing it. What looks like a simple task for nearly everyone else can be more of a tough challenge for Walgamott, who lost his left hand and a portion of his arm in an electrical accident 17 years ago.

But Walgamott was trying out the prototype of a high-tech prosthetic arm with fingers that not only can move but can also move with his thoughts. Owing to a biomedical engineering team at the University of Utah, he “felt” the egg quite well so his brain could tell the prosthetic hand not to grasp too tightly.

That is because the team, directed by U biomedical engineering associate professor Gregory Clark, has discovered a way for the “LUKE Arm” (christened after the robotic hand that Luke Skywalker was given in “The Empire Strikes Back”) to imitate the way a human hand feels objects by transmitting the correct signals to the brain.

Their findings were reported in a new paper co-authored by Utah’s biomedical engineering doctoral student Jacob George, former doctoral student David Kluger, Clark, and other colleagues in the recent edition of the journal Science Robotics.

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. We’re making more biologically realistic signals.

Jacob George, Doctoral Student, Biomedical Engineering, University of Utah

That means an amputee with the prosthetic arm would be able to sense the touch of something hard or soft, understand better how to pick it up and carry out delicate functions that would otherwise be unmanageable with a regular prosthetic with metal claws or hooks for hands.

“It almost put me to tears,” Walgamott recollects the first time he used the LUKE Arm during clinical tests in 2017. “It was really amazing. I never thought I would be able to feel in that hand again.”

Walgamott, a real estate agent from West Valley City, Utah, and one of seven test participants at the University, was able to pick grapes without crushing them, grasp an egg without damaging it, and hold his wife’s hand with a sensation in the fingers akin to that of an able-bodied person.

“One of the first things he wanted to do was put on his wedding ring. That’s hard to do with one hand,” says Clark. “It was very moving.”

Those things are realized through a complicated series of mathematical calculations and modeling.

The LUKE Arm

The LUKE Arm has been under progress for nearly 15 years. The arm itself is composed of mainly metal motors and parts with a clear silicon “skin” over the hand. It is driven by an external battery and wired to a computer. It was built by DEKA Research & Development Corp., a New Hampshire-based company set up by Segway inventor Dean Kamen.

Meanwhile, the Utah team has been designing a system that enables the prosthetic arm to tap into the wearer’s nerves, which are like biological wires that convey signals to the arm to move. It does that because of an invention by Utah’s biomedical engineering Emeritus Distinguished Professor Richard A. Normann called the Utah Slanted Electrode Array.

The array is a roll of 100 microelectrodes and wires that are embedded into the amputee’s nerves in the forearm and linked to a computer outside the body. The array deduces the signals from the still-remaining arm nerves, and the computer translates them to digital signals that instruct the arm to move.

But it also functions the other way. To do tasks such as picking up objects necessitates more than merely the brain instructing the hand to move. The prosthetic hand must also pick up how to “feel” the object so as to know how much pressure to apply because one cannot find that out merely by looking at it.

First, the prosthetic arm contains sensors in its hand that transmits signals to the nerves via the array to imitate the feeling the hand gets when grabbing an item. But equally crucial is how those signals are transmitted. It involves comprehending how the brain handles transitions in information when it first touches an object. Upon first touching an object, a spurt of impulses travels up the nerves to the brain and then tapers off. Recreating this was a massive step.

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.

Gregory Clark, Associate Professor, Biomedical Engineering, University of Utah

To realize that, Clark’s team used mathematical calculations together with recorded impulses from a primate’s arm to develop an approximate model of how humans receive these various signal patterns. That model was then added into the LUKE Arm system.

Future research

Besides developing a prototype of the LUKE Arm having a sense of touch, the entire team is already creating a version that is fully portable and does not have to be wired to a computer outside the body. Instead, the whole thing would be linked wirelessly, providing the wearer total freedom.

Clark says the Utah Slanted Electrode Array can also transmit signals to the brain for more than just the sense of touch, such as temperature and pain, though the paper mainly addresses touch. While their work presently involved only amputees who lost their extremities below the elbow where the muscles to move the hand are situated, Clark says their research could also be used even by those who lost their arms above the elbow.

Clark believes that in 2020 or 2021, three test participants will be able to have the arm for use, after federal regulatory approval.

The project involves many institutions including the U’s Department of Neurosurgery, Department of Physical Medicine and Rehabilitation and Department of Orthopedics, the University of Chicago’s Department of Organismal Biology and Anatomy, the Cleveland Clinic’s Department of Biomedical Engineering, and Utah neurotechnology companies Ripple Neuro LLC and Blackrock Microsystems. The project is sponsored by the Defense Advanced Research Projects Agency and the National Science Foundation.

This is an incredible interdisciplinary effort. We could not have done this without the substantial efforts of everybody on that team.

Gregory Clark, Associate Professor, Biomedical Engineering, University of Utah

(Video credit: University of Utah)