Made of fabric and rubber laced with sensors to mimic nerve endings, e-dermis recreates a sense of touch as well as pain by sensing stimuli and relaying the impulses back to the peripheral nerves.
“It's inspired by what is happening in human biology, with receptors for both touch and pain,” said Luke Osborn, a graduate student in biomedical engineering. “A prosthetic hand that is already on the market [can be fitted] 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.”
The work shows it’s possible to restore a range of natural, touch-based feelings to amputees who use prosthetic limbs. The ability to detect pain could be useful, for instance, not only in prosthetic hands but also in lower limb prostheses, alerting the user to potential damage to the device.
“Pain is, of course, unpleasant, but it’s also an essential, protective sense of touch that is lacking in the prostheses that are currently available to amputees,” Osborn said. “Advances in prosthesis designs and control mechanisms can aid an amputee’s ability to regain lost function, but they often lack meaningful, tactile feedback or perception.”
The e-dermis conveys information to the amputee by electrically stimulating peripheral nerves in the arm in a non-invasive way. Inspired by human biology, the e-dermis enables its user to sense a continuous spectrum of tactile perceptions, from light touch to noxious or painful stimulus.
The team created a ‘neuromorphic model’ mimicking the touch and pain receptors of the human nervous system, allowing the e-dermis to electronically encode sensations just as the receptors in the skin would. Tracking brain activity via electroencephalography, or EEG, the team determined that the test subject was able to perceive these sensations in his phantom hand.
In a pain-detection task the team determined that the test subject and the prosthesis were able to experience a natural, reflexive reaction to both pain while touching a pointed object and non-pain when touching a round object.
The e-dermis is not sensitive to temperature — for this study, the team focused on detecting object curvature (for touch and shape perception) and sharpness (for pain perception). Osborn says the technology could be used to make robotic systems more human, and it could also be used to expand or extend to astronaut gloves and space suits.
The researchers plan to further develop the technology and work to better understand how to provide meaningful sensory information to amputees in the hopes of making the system ready for widespread patient use.
