At a lab at Johns Hopkins University, researchers are building a prosthetic hand unlike any other: It can sense pain.
It’s easy to understand why you might want a prosthesis that can feel the squishiness of a grape or the warmth of another person’s hand. But pain? Well, pain could be useful, too. “If you think about how we humans use pain, it’s to protect our bodies, to prevent damage,” says Luke Osborn, a graduate student in Nitish Thakor’s lab at Hopkins, who co-authored a new paper on the pain-sensitive hand.
People born without the ability to feel pain stumble through life with dangerous freedom. Babies who do not feel pain are known to chew their fingers raw; children without pain will plunge their hands into boiling water. Pain is a signal that says, Hey, watch out. “People do damage their prosthetic limbs a lot. They use them as tools they weren’t designed to be used as,” says Levi Hargrove, a bioengineer at the Shirley Ryan AbilityLab, who was not involved in the study. It’s easy, for example, to bang an unfeeling piece of plastic and metal against a table. Pain could make a prosthesis feel more real, more lifelike—less a tool and more like a natural part of the body.
So Osborn and his collaborators set about making an “e-dermis,” an electronic skin that fits over the fingertips of a prosthetic hand. The e-dermis is a thin layer of rubber and fabric that senses pressure. It can “feel” the difference between a small round object and a sharp, pointy one, and converts the signal to a series of electric pulses.