A complex network of receptors relays sensations from fingertip to brain. Sharp. Round. Rough. Soft. Hot. Cold. The ability to detect pain, in particular, is vital to preventing bodily damage. Touch a hot stove or a shard of glass, and the message to move one's hand comes through loud and clear.
A new electronic skin designed by a team of Johns Hopkins engineers is helping return that sense of touch to amputees. When layered on top of prosthetic hands, this e-dermis, as it is called, laced with sensors to mimic nerve endings, registers stimuli and relays the impulses back to the peripheral nerves. "After many years, I felt my hand, as if a hollow shell got filled with life again," says the amputee who served as the team's principal volunteer.
"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," says Nitish Thakor, a professor of biomedical engineering and senior author of the research, which was recently published online in Science Robotics.
The fabric and rubber e-dermis works by electronically encoding sensations just as the receptors in the skin would. It then stimulates peripheral nerves in the arm, which are connected to the device using a noninvasive method known as transcutaneous electrical nerve stimulation. Inspired by human biology, the e-dermis could be useful for both prosthetic hands and lower limb prostheses, alerting the user to potential damage to the device. It is significant because it can fit overtop a prosthetic hand that's already on the market, meaning users can retrofit their existing device and replace the e-dermis if it ever gets damaged, says Luke Osborn, a graduate student in biomedical engineering and lead author of the research.
The research team includes members from the Johns Hopkins departments of Biomedical Engineering, Electrical and Computer Engineering, and Neurology, and from the Singapore Institute of Neurotechnology. For now, the e-dermis is not sensitive to temperature—the team focused instead on the ability to detect object curvature (for touch and shape perception) and sharpness (for pain perception). But they plan to further develop the technology, which could be used not only for amputees but to make robotic systems more human, to expand or extend to astronaut gloves and space suits, and more, Osborn says.