(Screenshot by Michelle Starr/CNET Australia)
A prosthetic hand taps into nerve bundles located in the arm to allow the wearer to "feel" with the prosthetic fingers.
Prosthetic hands are certainly getting advanced. Myoelectric prosthetics allow wearers to achieve a fine level of movement by reading the involuntary muscle contractions and moving accordingly — but there's one area where they haven't quite arrived. Without being able to feel what they are holding, it is much easier for users to damage or crush delicate objects.
A new bionic prosthetic, developed jointly by researchers at Cleveland Veterans Affairs Medical Center and Case Western Reserve University and led by associate professor Dustin Tyler, may go some way to solving this problem. It can convey a sense of touch from 20 separate regions on a single prosthetic hand using an electrical interface that directly stimulates peripheral nerves on the wearer's arm.
The interface consists of modified 7-millimetre cuff electrodes, into which are placed radial, median and ulnar nerve bundles. The cuff flattens the bundles, creating a larger surface area, and the 20 electrodes deliver signals to the nerve fibres, allowing the wearer to feel when they are touching something. This differs from previous nerve interfaces in that it doesn't penetrate the nerve sheath, lessening the chance of signal degradation and nerve damage.
So far, two people have been fitted with the hands, and they continue to work after 18 months. One of these people is 48-year-old Ohio man Igor Spetic, whose right hand was crushed beneath a drop-forging hammer while he was crafting an aluminium jet engine part. In the video below, you can see him removing stems from cherries — first with the sensation turned off and then with the sensation turned on. With the sensation turned off, he damages nine out of 15 cherries; with it turned on, he only damages one out of 15.
Northwestern University neuroscience professor Lee Miller, who was not involved with the research, said the hand was a strong achievement. "This is the greatest number of distinct touch sensations generated by peripheral nerve stimulation that I know of, and the 18-month-long stability is also unsurpassed," he said.
Professor Tyler and his team are preparing a paper on their research.