Electronic Skin Lets Amputees Feel Pain Through Their Prosthetics
28 June 2018
Researchers at Johns Hopkins University have created a new electronic dermis (e-dermis). When placed over a prosthetic device, this artificial skin lets amputees feel pain and other sensations in their missing limb.
The researchers published their study Wednesday in the journal Science Robotics.
To create an electronic skin that functions like human skin, the researchers started studying the interaction between brain and skin and noticed that our skin contains a network of receptors that relay a variety of sensations to the brain, letting us know if what we’re touching is sharp or smooth, hot or cold, hard or soft, and so on.
“After many years, I felt my hand, as if a hollow shell got filled with life again,” says the anonymous amputee who served as the team’s principal volunteer tester.
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.
“We’ve made a sensor that goes over the fingertips of a prosthetic hand and acts like your own skin would,” says Luke Osborn, a graduate student in biomedical engineering. “It’s inspired by what is happening in human biology, with receptors for both touch and pain.
“This is interesting and new,” Osborn said, “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.”
To provide sensory feedback, they used targeted TENS to extensively map and understand the perception of a transhumeral amputee’s phantom limb during sensory feedback, a method they previously demonstrated in multiple amputees.
Although the participant did not undergo any targeted muscle or sensory reinnervation during surgery, there was a natural regrowth of peripheral nerves into the remaining muscles, soft tissue, and skin around the amputation. The median and ulnar nerves were identified on the amputee’s left residual limb and targeted for noninvasive electrical stimulation because these nerves innervated relevant areas of the phantom hand. The participant received more than 25 hours of sensory mapping in addition to over 150 trials of sensory stimulation experiments to quantify the perceptual qualities of the stimulation. Extensive mapping of the residual limb showed localized activation of the amputee’s phantom hand.
The human body is a template for many state-of-the-art prosthetic devices and sensors. Perceptions of touch and pain are fundamental components of our daily lives that convey valuable information about our environment while also providing an element of protection from damage to our bodies. Advances in prosthesis designs and control mechanisms can aid an amputee’s ability to regain lost function but often lack meaningful tactile feedback or perception.
Through transcutaneous electrical nerve stimulation (TENS) with an amputee, we discovered and quantified stimulation parameters to elicit innocuous (nonpainful) and noxious (painful) tactile perceptions in the phantom hand. Electroencephalography (EEG) activity in somatosensory regions confirms phantom hand activation during stimulation.
We invented a multilayered electronic dermis (e-dermis) with properties based on the behavior of mechanoreceptors and nociceptors to provide neuromorphic tactile information to an amputee. Our biologically inspired e-dermis enables a prosthesis and its user to perceive a continuous spectrum from innocuous to noxious touch through a neuromorphic interface that produces receptor-like spiking neural activity. In a pain detection task (PDT), we show the ability of the prosthesis and amputee to differentiate nonpainful or painful tactile stimuli using sensory feedback and a pain reflex feedback control system.
In this work, an amputee can use perceptions of touch and pain to discriminate object curvature, including sharpness. This work demonstrates possibilities for creating a more natural sensation spanning a range of tactile stimuli for prosthetic hands.
The researchers plan to further develop the technology and better understand how to provide meaningful sensory information to amputees in the hopes of making the system ready for widespread patient use.
|Written by: Linda Wallers|