By Mark Waghorn via SWNS
A bionic arm has been created that combines intuitive motor control, touch and grip - producing the sensation of actually opening and closing a hand for amputees.
The brain-computer interface is the first to test all three functions all at once in a prosthetic device.
"They feel as if one of their hands are moving - even though they don't have a hand," said lead investigator Professor Paul Marasco, of the Cleveland Clinic in Ohio.
"They feel as if their fingers are touching things - even though they don't have fingers," Marasco said. "The interesting thing about it is when we put all of these systems together their brains actually feel like the hand is human."
It links to limb nerves which send impulses from the patient's brains to the prosthetic when they want to use or move it.
The robotic arm also receives physical information from the environment - relaying it back to their brain through their nerves.
"We modified a standard-of-care prosthetic with this complex bionic system which enables wearers to move their prosthetic arm more intuitively and feel sensations of touch and movement at the same time," Marasco said. "These findings are an important step towards providing people with amputation with complete restoration of natural arm function."
The bi-directional feedback and control allowed participants to perform tasks with a similar degree of accuracy as non-disabled peers.
"Perhaps what we were most excited to learn was that they made judgments, decisions and calculated and corrected for their mistakes like a person without an amputation," Marasco said. "With the new bionic limb, people behaved like they had a natural hand. Normally, these brain behaviors are very different between people with and without upper limb prosthetics."
It was tested on two study individuals with arm amputations who had previously undergone targeted sensory and motor re-innervation
The procedures establish a neural-machine interface by redirecting amputated nerves to remaining skin and muscles. Touching the skin with small robots activated sensory receptors that helped them perceive the sensation of touch.
When they thought about moving their limbs, the reinnervated muscles communicated with a computerized prosthesis to move in the same way.
The powerful machines also vibrated kinesthetic sensory receptors in those same muscles - leading them to 'feel' their hand and arm were moving.
Both participants were able to carry out basic, everyday tasks requiring hands and arms wearing the prosthetic.
They ranged from picking up and using cups, bottles and pegs to grasping a pen to write with.
One of the volunteers even used a smartphone. Describing the sensation, Claudia Mitchell, 41, said: "When I lean it back it's touching my 'finger'.
"I can actually tell which one. I can feel that."
Mitchell, who lives in Arkansas, said the new arm has made a "huge difference" in her life.
Everyday activities like opening and grabbing a water bottle and cutting a peach to make a pie are now much easier.
The US Marine veteran lost her left arm at the shoulder in a 2004 motorcycle accident.
She can also adeptly pick up a make-up bag using her prosthetic thumb and forefinger - and feel an object and know how hard to grip it.
"They were activities I once thought would never again be possible," Mitchell said.
Driven by medical technology that sounds like it could be from a science-fiction movie, her customized prosthetic is outfitted with a powerful computerized robotic touch system.
More than a prosthetic, it's actually part of her. She can interact with other people in a natural way.
Advanced evaluation tools showed the volunteers' performances were better than people with amputations using traditional prosthetic devices.
They were even comparable to those of non-disabled people, said the international team.
The other participant was wildfire ranger Rob Anderson, 43, from Grande Prairie, Alberta, Canada.
The pair were also assessed when the three sensory and motor modalities were enabled together versus individually.
As people with traditional prosthetics cannot feel with their limbs, they behave differently than those without an amputation while completing daily chores.
For example, they must constantly watch their device while using it, Marasco explained. They also have trouble learning to correct mistakes when they apply too much or too little force with their hand.
With the new artificial arm the researchers could see the pairs' brain and behavioral strategies changed to match those of a person without an amputation.
They no longer needed to watch their prosthesis, they could find things without looking and they could more effectively correct for mistakes.
"Over the last decade or two, advancements in prosthetics have helped wearers to achieve better functionality and manage daily living on their own," Marasco said. "For the first time, people with upper limb amputations are now able to again 'think' like an able-bodied person, which stands to offer prosthesis wearers new levels of seamless reintegration back into daily life."
The analysis in Science Robotics can be applied to any upper limb prosthetic or deficit that involves sensation and movement.
"We built the system actually using an off the shelf prosthetic as our basis," Marasco said. "Then we put in high level computing, touch and movement sensation. When you look at the limb it actually looks like any other. You can't tell there's actually a highly sophisticated, computerized communication and feedback system running inside of that."
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