Controller gives steady sensory feedback to prosthetic arms

April 27 (UPI) — Researchers have developed a prosthetic arm setup that allows the user to feel steady sensation from mild electrical feedback that stimulates nerves.

University of Illinois at Urbana-Champaign team members developed a control algorithm that regulates the current, and it still works even when the electrodes begin to peel off or sweat builds up. Their findings were published this week in the journal Science Robotics.

“We’re giving sensation back to someone who’s lost their hand,” lead study author Aadeel Akhtar, an M.D./Ph.D. student in the neuroscience program at the University of Illinois said in a press release. “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.

Akhtar also founded PSYONIC, a startup company that develops low-cost bionic arms, and ultimately hopes to have the control system totally covered by health insurance.

He said a controlled stimulation module would cost much less than the prosthetic itself.

“Commercial prosthetics don’t have good sensory feedback,” Akhtar said. “This is a step toward getting reliable sensory feedback to users of prosthetics.”

Other prosthetic arms have included nerve stimulation with sensors in the fingertips, allowing the user to feel the amount of pressure the arm exerts. The harder the pressure, the stronger the signal.

But these arms haven’t given reliable feedback. The electrodes connected to the skin peel off, giving the user painful shocks. And sweat can block the connection between the electrode and the skins.

“A steady, reliable sensory experience could significantly improve a prosthetic user’s quality of life,” principal investigator Timothy Bretl, an aerospace engineering professor, said.

With the newly developed arm, a controller adjusts the current level by monitoring the situation. It works even when 75 percent of the electrodes are peeled off.

Two volunteers tested the system. Tasks included climbing stairs, hammering a nail into a board and running on an elliptical machine that could cause sweat and a loss of sensation. In addition, some of the electrodes progressively peeled back and forth.

“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,” Akhtar said. “However, when we had the control algorithm on, after the activity they said they could still feel the sensation just fine.”

The group wants the device to be so small it fits inside the arm rather than attaching to the outside.

“Once we get a miniaturized stimulator, we plan on doing more patient testing where they can take it home for an extended period of time and we can evaluate how it feels as they perform activities of daily living,” Akhtar said. “We want our users to be able to reliably feel and hold things as delicate as a child’s hand.”

He said the goal is “making a prosthetic hand that becomes an extension of the body rather than just being another tool.”

Researchers at the Cleveland Clinic have developed a prosthetic arm with more natural movement sensation. In tests on volunteers, users can “feel” their palm, back of the hand and even felt each finger, according to researchers.