A Cleveland Clinic led international research team have engineered a first-of-its-kind bionic arm for patients with upper-limb amputations that allows the wearer to control the arm with their thoughts and feel the sensations of touch and movement.
The bionic system combines three important functions – intuitive motor control, touch and grip kinaesthesia, and the intuitive feeling of opening and closing the hand.
The system is the first to test all three sensory and motor functions in a neural-machine interface all at once in a prosthetic arm. The neural-machine interface connects with the wearer’s limb nerves. It enables the patient to send nerve impulses from their brain to the prosthetic when they want to use or move it, and to receive physical information from the environment and relay it back to their brain through their nerves.
The artificial arm’s bi-directional feedback and control enabled study participants to perform tasks with a similar degree of accuracy as non-disabled people.
“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,” said lead investigator Paul Marasco, Ph.D., associate professor in Cleveland Clinic Lerner Research Institute’s Department of Biomedical Engineering. “With the new bionic limb, people behaved like they had a natural hand. Normally, these brain behaviours are very different between people with and without upper limb prosthetics.”
The researchers tested their new bionic limb on two study participants with upper limb amputations who had previously undergone targeted sensory and motor reinnervation-procedures that establish a neural-machine interface by redirecting amputated nerves to remaining skin and muscles.
In targeted sensory reinnervation, touching the skin with small robots activates sensory receptors that enables the patient to perceive the sensation of touch. In targeted motor reinnervation, when the patient thinks about moving their limbs, the reinnervated muscles communicate with a computerized prosthesis to move in the same way. Additionally, small, powerful robots vibrate kinaesthetic sensory receptors in those same muscles which helps the wearer feel that their hand and arm are moving.
According to Dr. Marasco, because people with traditional prosthetics cannot feel with their limbs, they behave differently to people without an amputation while completing tasks during daily living. For example, traditional prosthesis wearers must constantly watch their prosthetic while using it and have trouble learning to correct for mistakes when they apply too much or little force with their hand.
With the new artificial arm and the advanced evaluation tools, the researchers could see that the study participants’ brain and behavioural 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 their mistakes.
“Over the last decade or two, advancements in prosthetics have helped wearers to achieve better functionality and manage daily living on their own,” said Dr. Marasco. “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 study was funded in part by the Defense Advanced Research Projects Agency, a research and development arm of the U.S. Department of Defense.
