Scientists from the Lerner Research Institute at the Cleveland Clinic have developed a bionic arm allowing upper-limb amputees to simultaneously feel sensations of movement and touch. This lets them think, behave and function like a person who doesn't have an amputation. The research team, led by the Cleveland Clinic, includes collaborators from the University of Alberta and the University of New Brunswick. They all contributed to engineering a bionic system that integrates motor control, touch and grip kinesthesia — the feeling of opening and closing the hand.
"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 movement and touch at the same time. These findings are an important step towards providing people with amputation with complete restoration of natural arm function," said lead investigator Paul Marasco, Ph.D., who is an associate staff member at the institute's Department of Biomedical Engineering.
The system is the first of its kind to simultaneously test all three sensory and motor functions in a neural-machine interface in a prosthetic arm. The neural-machine interface connects with the wearer's limb nerves, letting them receive physical sensations from their environment with the prosthetic and send nerve impulses from their brain to the device, signalling when they want to move it. As a result, the artificial limb enabled research participants to achieve a similar degree of accuracy in carrying out motor tasks the way non-disabled people do.
The scientists tested the bionic arm on two upper-limb amputees who underwent targeted sensory and motor reinnervation, procedures that establish a neural-machine interface by redirecting amputated nerves to intact skin and muscle. In target reinnervation, surgeons take the severed ends of a patient's existing sensory or motor neurons that were a part of the missing limb and connect them to the axons of sacrificial sensory neurons performing tasks on a patient's remaining skin and muscles. This creates spots on the skin that the brain perceives as belonging to the missing parts of a person's amputated limb.
When participants used the new artificial arm, researchers saw that the individuals' thought processes and behaviour changed to match that of a non-amputee, resulting in them not needing to monitor their prosthesis as they move around, locating items without looking at their artificial limb and efficiently correcting mistakes in movement. This is different from what wearers of traditional prosthetic limbs experience as they have to watch their prosthesis as they are using it and struggle to correct mistakes in applying the wrong amount of force with their hands.
"Over the last decade or two, advancements in prosthetics have helped wearers to achieve better functionality and manage daily living on their own. 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," said Dr. Marasco.
Written by Sophia Lopez
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