New electronic skin gives prosthetics a sense of pain

Today's prosthetic devices don't allow users to perceive touch but a group of scientists from Johns Hopkins University developed a skin for devices that captures a range of sensations we experience, including pain for the first time. Their research is published today in Science Robotics.

The big picture: Over the past decade researchers have gained a better understanding of our "highly complex sense" of touch and worked on ways to add it to prosthetics, says Paul Marasco, a neurophysiologist at the Cleveland Clinic who wasn't involved in the work. Now, he adds, they are starting to trickle out of the research environment and into the clinical realm.

"Pain is a crucial part of our senses," says Luke Osborn, a graduate student at Johns Hopkins University. It is our way of protecting ourselves from further damage and gauging safety, he added.

What they did: Osborn and his colleague created an electronic skin or "e-dermis" that fits over a prosthetic hand. Like the human type, the engineered dermis has two layers that together mimic receptors on our body and captures a range of touch sensations, including pain.

• Working with an amputee volunteer, Osborn applied electric pulses that stimulated the participant's nerves and asked him to rate the level of discomfort from the sensation in his phantom hand. (In the experiment, they limited the pain to one you might experience if you accidentally cut yourself with a knife, Osborn says.)
• They then used those stimulation patterns to provide sensory feedback to the volunteer's brain as he picked up smooth, curved objects or sharp, pointed ones with his prosthetic hand.
• The researchers also gave the prosthetic a reflex so it would quickly let go of an object if it felt pain.

The challenge: Touch is made of multiple components, including pressure, vibration and temperature, and there are anywhere from 11 to 20 different channels ("depends on who you ask," Marasco says) for perceiving it.

• For example, the receptors on the back of our hand are different from those on our palms. All of that information is fused and integrated in the brain in order to make sense of the world, Marasco says. "Our fingers don't feel touch, our brain does."

One more thing: Osborn says the ability to sense pain could be useful for robots. It might allow them to differentiate between something that is potentially damaging and something that isn't, giving them more human-like touch.