An experimental new prosthetic limb has given wearers the ability to experience the sense of touch from the prosthetic, reports Technology Review. Normally, prosthetic limbs can help amputees regain some of the abilities of a lost limb. But touch is not among those abilities, because the prosthetic doesn't interface with the nervous system like a flesh-and-blood limb. This prototype prosthetic hand, however, created by researchers at the Cleveland Veterans Affairs Medical Center and Case Western Reserve University, can convey a sense of touch in 20 different spots on the hand.
"It does this by directly stimulating nerve bundles—known as peripheral nerves—in the arms of patients; two people have so far been fitted with the interface," writes Technology Review. "What’s more, the implants continue to work after 18 months, a noteworthy milestone given that electrical interfaces to nerve tissue can gradually degrade in performance."
The prosthetic is the first of its kind to create lasting nerve stimulation over such a long period, and may also have set a record for the number of distinct touch sensations it can recognize. It uses a piece of technology called a cuff electrode, which holds a bundle of nerve fibers. "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," explains Technology Review.
Other experiments with nerves penetrate the sheath to make contact with the electrons, which offers the potential for a "higher resolution" touch sensation, but is more likely to degrade the signal path. This experiment's approach proves the value of an alternative method, given its 18 months of functionality.
One test subject was able to successfully pluck the stems from cherries without applying too much pressure to them, as seen in the video below. He also experienced a variety of sensations with the prosthetic that were produced by modifying electrical signals, ranging from the soft sensation of a cotton ball to the rough texture of sandpaper.