Scientists Develop Ultra-Precise Mind-Controlled Prosthetic Limb

(CN) – The next generation of mind-controlled prosthetics are within reach and will give amputees the ability to better operate bionic limbs. All it will take is a learning algorithm and some muscle power.

The new technology detailed in a paper published Wednesday is more effective and resilient than previous attempts to link brain activity to prosthetic limb movement.

Joe Hamilton, a participant in the University of Michigan RPNI study, naturally uses his mind to control a DEKA prosthetic hand to pick up a small block. (Evan Dougherty / University of Michigan Engineering)

An able-bodied person carries out their daily actions effortlessly and without much thought to the network of nerves required to move their thumbs, fingers or hands. And yet it’s a process that does not go away after someone loses a limb.

Researchers with the University of Michigan developed a new surgical procedure that takes a tiny portion of a thigh muscle, grafts it into an amputee patient and allows severed nerves to develop new tissue. This allows for nerve signals to be amplified and better communicate with a bionic hand in a lab setting, according to the paper published in Science Translational Medicine.

This regenerative peripheral nerve interface (PRNI) technology acts as a megaphone for the severed nerves, the study authors say, allowing participants to carry out fine-motioned actions like picking up a small block or moving a zipper. U of M associate professor and study co-lead Cindy Chestek says typically other direct nerve approaches have only produced small nerve signals.

With the PRNI process the results were multiplied with greater results, Chestek said in an interview.

“Here, the muscle acts like a biological amplifier and makes it a 10-100 times bigger voltage,” Chestek said. “I think it’s safe to say that these are the largest nerve signals recorded to date in a human being, and that’s primarily what’s behind what we show for example controlling multiple degrees of freedom of the thumb.”

After the initial surgery, Chestek says all the participants said they felt like they were able to move their “phantom” hand. Each person was shown an animated hand movement and they were asked to follow along. After the initial calibration the participants were able to use the bionic hand for up to 300 days in the lab study, according study results.

Karen Sussex, a participant in the University of Michigan RPNI study, naturally uses her mind to control a Touch Bionics i-LIMB prosthetic hand to pick up a can of tomato paste. (Robert Coelius / University of Michigan Engineering)

The study is a sort of marriage between learning algorithm from the brain-machine interface field and the muscle grafts. Chestek, whose expertise is in the process of translating neural signals into movement intent, says all of the “learning” is in the algorithm parameters, and the study team only asked the participants to move as they normally would.

Study participant Joe Hamilton lost his arm in a fireworks accident in 2013. In a statement accompanying the study, Hamilton said, “It’s like you have a hand again. You can pretty much do anything you can do with a real hand with that hand. It brings you back to a sense of normalcy.”

Biomedical engineering professor Paul Cederna at U of M said in a statement that researchers often do not see how their work impacts a person.

“When you can sit and watch one person with a prosthetic device do something that was unthinkable 10 years ago, it is so gratifying. I’m so happy for our participants, and even more happy for all the people in the future that this will help,” Cederna said.

Chestek said the study is the result of 12 years of work that evaluated the surgical technique in animals and progressed to this clinical trial. There’s optimism that the findings to amplify nerve signals will have far-reaching implications for the field of prosthetics.

“We hope that one day this can become widely available, as this nerve amplification technique is applicable to basically every amputee at all levels, wherever the nerves are located,” said Chestek.

The team are looking for more participants as the trial is ongoing.

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