An international team of engineers has designed a soft, lightweight, and potentially low-cost neuroprosthetic hand that can help amputees with a wide range of daily activities, such as zipping a suitcase, shaking hands, and petting a cat.
The team from the Massachusetts Institute of Technology (MIT) in the US and the Shanghai Jiao Tong University in China developed the prosthetic, designed with a system for tactile feedback, restoring some primitive sensation in a volunteer’s residual limb. The new design is also durable, quickly recovering after being struck with a hammer or run over with a car.
The smart hand is soft and elastic and weighs about half a pound. Its components total around $500 — a fraction of the weight and material cost associated with more rigid smart limbs.
“This is not a product yet, but the performance is already similar or superior to existing neuroprosthetics, which we’re excited about,” said Xuanhe Zhao, Professor of mechanical engineering and of civil and environmental engineering at MIT.
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“There’s huge potential to make this soft prosthetic very low cost, for low-income families who have suffered from amputation,” Zhao added.
The artificial hand, described in the journal Nature Biomedical Engineering, is made from soft, stretchy material — the commercial elastomer EcoFlex. The prosthetic comprises five balloon-like fingers, each embedded with segments of fiber, similar to articulated bones in actual fingers. The bendy digits are connected to a 3-D-printed “palm,” shaped like a human hand.
Rather than controlling each finger using mounted electric motors, as most neuroprosthetics do, the researchers used a simple pneumatic system to precisely inflate fingers and bend them in specific positions. This system, including a small pump and valves, can be worn at the waist, significantly reducing the prosthetic’s weight.
The team used an existing algorithm that “decodes” muscle signals and relates them to common grasp types to program the controller for their system.
When an amputee imagines, for instance, holding a wine glass, the sensors pick up the residual muscle signals, which the controller then translates into corresponding pressures. The pump then applies those pressures to inflate each finger and produce the amputee’s intended grasp.
To enable tactile feedback, the team stitched to each fingertip a pressure sensor, which when touched or squeezed produces an electrical signal proportional to the sensed pressure. Each sensor is wired to a specific location on an amputee’s residual limb, so the user can “feel” when the prosthetic’s thumb is pressed, for example, versus the forefinger.