Neuroprosthesis technology has advanced over the years, but it is still not accessible enough for the vast majority of the population. Now engineers at MIT and Shanghai Jiao Tong University have designed a soft, lightweight, and potentially low-cost neuroprosthetic hand.
The prosthetic hand precisely inflates individual fingers to take hold of objects while also providing the user with tactile feedback. The smart hand is soft and elastic, weighs about half a pound, and has a total component cost of about US$500 – making it potentially more affordable, as well as easier to use, if or when it goes into production.
The team’s artificial hand is made from soft, stretchy material – in this case, the commercial elastomer EcoFlex. It comprises five balloon-like fingers, each embedded with bone-like fiber segments. The bendy digits are connected to a 3D-printed palm, shaped like a human hand.
Unlike other neuroprosthetic models with electric motors, this prototype uses 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.
Using a computer model, the team developed a controller that directs the pneumatic system to inflate the fingers in positions that mimic five common grasps, including pinching two and three fingers together, making a balled-up fist, and cupping the palm.
The pneumatic system receives signals from EMG (electromyography) sensors attached to the user’s limb that measure electrical signals generated by motor neurons to control muscles. The team then used an existing algorithm that “decodes” muscle signals into common grasp types to program the controller for common tasks, such as holding a wine glass. When an amputee imagines, the sensors pick up the residual muscle signals, which the controller then translates into corresponding pressures. Each finger is then inflated by the pump to create the required grasp shape.
They stitched to each fingertip a pressure sensor and then wired them all up to a specific location on an amputee’s residual limb to provide real-time tactile feedback.
The volunteers learned to use it by repeatedly contracting the muscles in their arms while imagining making five common grasps. After 15 minutes of training, they found themselves stacking checkers, turning pages, writing with a pen, lifting heavy balls, and picking up fragile objects like strawberries and bread. They repeated the same tests using a more rigid, commercially available bionic hand and found that the inflatable prosthetic was as good, or even better, at most tasks, compared to its rigid counterpart.
The team has filed a patent on the design through MIT and is working to improve its sensing and range of motion.
“This is not a product yet, but the performance is already similar or superior to existing neuroprosthetics, which we’re excited about,” says Xuanhe Zhao, professor at MIT. “There’s huge potential to make this soft prosthetic very low cost, for low-income families who have suffered from amputation.“