Over the past few years, artificial hands have come a long way in terms of dexterity. They can grasp, shake hands, point, and, usefully, make the "come hither" gesture.
Now, researchers at the Cleveland Veterans Affairs Medical Center and Case Western Reserve University have made significant progress in building a prosthetic hand that provides something like a sense of touch.
The hand, which you can see put to use in a demonstration in the video below, has 20 sensitive spots that can perceive other objects' physicality. Implants that connect those spots to nerves in the patients arm have continued to work 18 months after installation, which MIT Technology Review reports, notes is a important milestone since "electrical interfaces to nerve tissue can gradually degrade in performance."
Hands are more than tools for manipulating the physical world. They are also tools of perception, reporting sensations such as heat, texture, contact. These two systems, output and input, work together, helping us to know when our grasp is tight or whether we've reached the object on a shelf that's just out of view. The difficulty of building a machine that can perceive tactile information and report it back to the brain has become the roadblock for a truly hand-like prosthetic.
The new prosthetic is a step towards creating this feedback loop. And it can do more than sense simple contact. Dustin Tyler, of Case Western, can adjust the device to signal different textures. Igor Spetic, who is using the hand in the above video, "says sometimes it feels like he’s touching a ball bearing, other times like he’s brushing against cotton balls, sandpaper, or hair," according to the Technology Review report.
At the heart of the technology is a custom version of an interface known as a cuff electrode. Three nerve bundles in the arm—radial, median, and ulnar—are held in the seven-millimeter cuffs, which gently flatten them, putting the normally round bundles in a more rectangular configuration to maximize surface area.
Then a total of 20 electrodes on the three cuffs deliver electrical signals to nerve fibers called axons from outside a protective sheath of living cells that surround those nerve fibers. This approach differs from other experimental technologies, which penetrate the sheath in order to directly touch the axons. These sheath-penetrating interfaces are thought to offer higher resolution, at least initially, but with a potentially higher risk of signal degradation or nerve damage over the long term. And so they have not been tested for longer than a few weeks.
Thus far, the device has only been tested in the lab, but researchers are hoping that further development and study could bring it to the market within the next decade.