Losing a limb can be devastating, made all the worse by prosthetics that are far from mirroring a natural limb and end up being rejected by the amputee. Researchers have developed a bionic limb with never before seen sensory capabilities – fusing intuitive motor control, touch, and the feeling of opening and closing the hand (grip kinesthesia) for patients with upper-limb amputations. These factors working together provide a higher-level behavioral performance akin to a non-disabled person.
Amputations often have an overwhelming impact on patients’ health with the potential to cause psychological distress, economic loss, difficult reintegration into society, and rejection of their prosthetic replacement.
Rejection of a prosthetic limb is where the prosthesis is viewed as a foreign body by its user instead of a prosthetic embodiment involving the full integration of the bionic limb into the patient’s psyche. As these robotic appendages can’t mimic the body’s ability to sense the movement, action, and location of human upper limb function, work is underway to improve full prosthetic integration. But with cases concerning artificial limb repulsion on the rise, new, more efficient prosthetics are needed that patients would readily accept.
Now, a study from researchers led by the Lerner Research Institute engineers a first-of-its-kind bionic arm for patients with upper-limb amputations that allows wearers to think, behave and function as a person without an amputation. The team modified a standard-of-care prosthetic with this complex neural interface enabling wearers to move their prosthetic arm more intuitively while feeling the sensations of movement and touch. The study is published in the journal Science Robotics.
Previous studies show that although prostheses are used to at least partially restore the body cosmetically after amputation, hurdles exist regarding the patient’s acceptance of their prosthetic device as part of their body. As can be expected, this is a crucial part of prosthetic rehabilitation.
Due to the fact, people with traditional prosthetics can’t feel with their limbs – they behave differently to people without an amputation while completing tasks during daily living. For example, conventional prosthesis wearers must constantly watch their prosthetic while using it and have trouble correcting mistakes when applying too much or little force with their hands. Thus, the artificial limb may start to feel alien to the user.
A possible remedy, targeted sensory reinnervation via a neural interface, consists of touching the skin with small robots to activate sensory receptors, which enable the sensation of touch. In targeted motor nerve restoration, when patients think about moving their limbs, the reinnervated muscles communicate with a robotic prosthesis via the neural interface to move in the same way. Likewise, small, powerful robots vibrate kinesthetic sensory receptors in those same muscles, which helps prosthesis wearers feel that their hands and arm are moving.
The current study develops a bionic arm system that combines motor control, touch and grip kinethesia reinnervation. To achieve this, the researchers tested their new bionic limb on two participants with upper-limb amputations. Both volunteers had previously undergone targeted sensory and motor reinnervation to establish a closed-loop neural-machine interface diverting amputated nerves to the remaining skin and muscle.
The patients performed everyday behaviors requiring hand and arm functionality while wearing the advanced prosthetic – they did this without having to watch their prosthesis, find things without looking, or correct their mistakes more effectively. In a groundbreaking result, the study participants’ brain and behavioral strategies changed to match a person without an amputation.
The system differs from others as it’s the first to test all three sensory and motor functions in a prosthetic arm at once. These tests are all facilitated by a brain-computer interface connected to the wearer’s nerves in their limb – enabling patients to send nerve impulses from their brains to the prosthetic. In this way, they can use or move their prosthesis while receiving physical information from the environment and relaying it back to their brain through their nerves.
The lab explains how their sensory bionics will change amputee’s lives. “Perhaps what we’re most excited to learn was that they made judgments, decisions and calculated and corrected for their mistakes like a person without an amputation,” said Dr. Marasco, who leads the Laboratory for Bionic Integration. “With the new bionic limb, people behaved as if they had a natural hand. Normally, these brain behaviors are very different between people with and without upper limb prosthetics.”
“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.”
In the future, the researchers state their findings are an essential step towards providing amputees with complete restoration of natural arm function.
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