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Amputees use thought to move individual fingers in bionic limb

Scientists have developed a new ‘nerve interface’ technology that allows users to have greater control and precision when using prosthetic hands.

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

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

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

A new piece of technology that allows amputees to move individual fingers in their prosthetic limbs by using their mind has been developed by scientists.

The so called “nerve interface” technology uses muscle grafts, electrodes and machine learning algorithms to amplify the faint nerve signals coming from the amputee’s residual limb so the bionic hand can receive these signals in real time.

The US researchers said their technology, which can last for almost a year without adjustments, allows amputees to have more precision control of their prosthetic hands.

Dr Robert Oneal, a collegiate professor of plastic surgery at the University of Michigan’s Medical School in the US and study co-author said: “This is the biggest advance in motor control for people with amputations in many years.

“We have developed a technique to provide individual finger control of prosthetic devices using the nerves in a patient’s residual limb.

“With it, we have been able to provide some of the most advanced prosthetic control that the world has seen.”

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

Four participants were involved in the study published in the journal Science Translational Medicine.

All the test subjects used the Mobius Bionics LUKE arm developed by a medical device company based in the US.

As the peripheral nerve signals in an amputated limb are too faint to be picked up by the electrodes, the researchers found a way to amplify these signals wrapping the nerves in tiny muscle grafts.

These muscle grafts then regenerated and developed nerves and blood vessels over three months, which prevented the growth of nerve masses that lead to phantom limb pain.

Electrodes implanted in the muscle grafts were able to record the peripheral nerve signals and pass them on to a prosthetic hand in real time.

Dr Oneal said: “We designed a way to connect up the peripheral nerves with a piece of muscle.

Joe Hamilton, a participant in the University of Michigan RPNI study, naturally uses his mind to control a DEKA prosthetic hand to pinch a small zipper on a hand development testing platform
Study participant Joe Hamilton uses his mind to control his prosthetic hand to pinch a small zipper on a hand development testing platform (Evan Dougherty/University of Michigan Engineering)

“When a tiny peripheral signal comes down the nerve it goes down to the muscle and becomes a huge muscle signal.”

In the lab, the participants were able to pick up blocks with a pincer grasp and move their thumb in a continuous motion using their thought.

In addition, they were able to lift round objects and even play a version of the rock, paper, scissors game.

Dr Cindy Chestek, an associate professor of biomedical engineering at the University of Michigan’s College of Engineering, and one of the study authors, said: “So now we can access the signals associated with individual thumb movement, multidegree of freedom thumb movement, individual fingers.

“This opens up a whole new world for people who are upper limb prosthesis users.”

The researchers said their nerve interface worked for up to 300 days without requiring readjustments.

Study participant Joe Hamilton, who lost his arm in a fireworks accident in 2013, 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.”

The researchers are now looking for new participants as part of an ongoing clinical trial.

PA