Researchers have developed an "e-dermis" or electronic skin that could be applied to a prosthetic hand to give the wearer a sense of touch. By using electronic sensors that mimic the nerve endings in the body, the skin can convey both the senses of touch and of pain.
The skin is made of a combination of fabric and rubber, into which the electronic sensors are embedded. The technology isn't invasive, but relays sensation through the wearer's skin using a method known as TENS, or transcutaneous electrical nerve stimulation – a process that needs hours of mapping of the subject's nerve endings.
It's thought the technology could make sense of so-called phantom limb sensations in amputees – the name given to the feeling that a missing limb remains present. The researchers used EEGs to confirm that phantom-limb sensations were felt during stimulation via the electronic skin over the course of tens of hours of testing.
According to the research paper, the subject mainly felt sensations of pressure along with some "electrical tingling" feelings. The subject reported feeling nothing more severe than an uncomfortable but tolerable pain. The researchers say the subject could report which fingers of the prosthesis were being stimulated "with perfect accuracy."
"For the first time, a prosthesis can provide a range of perceptions from fine touch to noxious to an amputee, making it more like a human hand," senior author of the research Nitish Thakor explains in a press release.
The desire to restore pain may seem counterintuitive, but it could be used to warn the wearer of damage.
"This is interesting and new, because now we can have a prosthetic hand that is already on the market and fit it with an e-dermis that can tell the wearer whether he or she is picking up something that is round or whether it has sharp points," adds biomedical student Luke Osborn.
"After many years, I felt my hand, as if a hollow shell got filled with life again," says the researchers' principle (and anonymous) volunteer.
At the moment the electronic skin is able to detect curvature and differentiate sharp objects, but in future could be adapted for temperature sensitivity. As well as helping prosthesis users, the researchers think the technology could be used to improve space suits, or to aid robots.
We've reported on various touch-sensitive prostheses over the years, but this development shows just how far the technology has come, needing no invasive surgery, differentiating touch from pain, and being potentially applicable to any prosthesis.
The skin is the work of a team of engineers at Johns Hopkins University and the Singapore Institute of Neurotechnology. The work has been published in the journal Science Robotics and can be read in full online.
A video summary can be seen below.
Sources: Johns Hopkins University, Science Robotics
