Prosthetic research could give amputees consistent, delicate sensation

Amputees could once again consistently feel things as delicate as a child’s hand in their own thanks to developing new research.

Led by neuroscientist Aadeel Akhtar, researchers at the University of Illinois in the US created a controller algorithm that regulates current from a prosthetic arm.

The artificial limbs replicate the sense of touch by stimulating nerves with mild electrical feedback. Sensors in the fingertips measure the amount of pressure exerted – a light touch generates a light sensation, while a hard push creates a stronger signal.

Over time, however, electrodes connected to the skin can start to peel off. This causes a build up of electrical current on the area that remains attached, potentially leading to painful shocks. Alternatively, sweat can block the connection so the user feels less or even nothing at all.

The researchers aimed to provide amputees with “steady, reliable sensory experience” to improve their quality of life. The controller algorithm monitors feedback the user experiences, automatically adjusting the current level so they feel steady feedback, even when sweating or when electrodes are 75% peeled off.

“We're giving sensation back to someone who's lost their hand,” said Akhtar, who is also founder of Psyonic, a company developing low-cost bionic arms. “The idea is that we no longer want the prosthetic hand to feel like a tool, we want it to feel like an extension of the body.”

The team tested the controller on two volunteers. In one test, the electrodes were progressively peeled back and the controller adjusted the electrical current to provide steady feedback without shocks.

The patients also did a series of tasks that could cause loss of sensation due to sweat – climbing stairs, hammering a nail into a board and running on a cross-trainer.

“What we found is that when we didn't use our controller, the users couldn't feel the sensation anymore by the end of the activity. However, when we had the control algorithm on, after the activity they said they could still feel the sensation just fine,” Akhtar said.

Now, the team is working on miniaturising the electric feedback module and hope to do more extensive patient testing. The aim is for users to reliably feel and hold things as delicate as a child’s hand.

The research was published in Science Robotics.