Amputees often experience the sensation of a “phantom limb” — a feeling that a missing body part is still there. Pain, while unpleasant, is an essential, protective sense of touch that is lacking in the prostheses that are currently available to amputees. 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.
An electronic skin was developed that, when layered on top of prosthetic hands, brings back a real sense of touch through the fingertips. Made of fabric and rubber laced with sensors to mimic nerve endings, the “e-dermis” recreates a sense of touch as well as pain by sensing stimuli and relaying the impulses back to the peripheral nerves. The sensor goes over the fingertips of a prosthetic hand and acts as the person’s own skin would.
Human skin is made up of a complex network of receptors that relay a variety of sensations to the brain. Bringing a more human touch to modern prosthetic designs is critical, especially when it comes to incorporating the ability to feel pain. That’s where the e-dermis comes in, conveying information to the amputee by stimulating peripheral nerves in the arm, making the so-called phantom limb come to life. 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 e-dermis does this by electrically stimulating the amputee’s nerves in a noninvasive way, through the skin. A neuromorphic model was made, mimicking the touch and pain receptors of the human nervous system and allowing the e-dermis to electronically encode sensations just as the receptors in the skin would. Tracking brain activity via electroencephalography (EEG), it was determined that the test subject was able to perceive these sensations in his phantom hand.
The researchers then connected the e-dermis output to the volunteer using a noninvasive method known as transcutaneous electrical nerve stimulation (TENS). In a pain-detection task, the team determined that the test subject and the prosthesis were able to experience a natural, reflexive reaction to 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). The technology could be used to make robotic systems more human and to expand or extend to astronaut gloves and spacesuits.