Restoring sensation for people with prosthetic hands

May 14, 2015

A macro-sieve peripheral nerve interface, modeled in this illustration, will stimulate regeneration of the ulnar and median nerves to transmit information from hands into the central nervous system (credit: Dan Moran, PhD, Washington University in St. Louis)

A team of engineers and researchers at Washington University in St. Louis is developing a device to restore sensory feedback for those qwith upper limb prosthetic devices, allowing people to feel touch, and hot and cold through their prosthetic hands.

If it works, upper-limb amputees who use motorized prosthetic devices would be able to feel various sensations through the prosthetic by stimulating the nerves in the upper arm and forearm, which would send sensory signals to the brain.

With a nearly $1.9 million grant from DARPA, the team has developed a peripheral nerve interface designed to stimulate regeneration of the ulnar and median nerves to transmit information back into the central nervous system.

An ultrathin, flexible material electrode similar to a soft contact lens and is about 1/8th the size of a dime is implanted into the ulnar and median nerves of anesthetized nonhuman primates.

The electrode, which looks like a wagon wheel with open spaces between the “spokes,” allows the nerve to grow. A small cuff electrode, the current standard of care, will compare the performance.

Once implanted, the team will train the nonhuman primates to play a joystick-controlled video game in which the team will give them cues as to where to move the joystick by stimulating specific sectors in the ulnar and median nerves so it feels as if someone is touching them. Their reward for advancing through the various stages of the game successfully is fruit-flavored juice.

The research team will then determine the amount of sensory information that is encoded, by providing low levels of stimulation to small groups of peripheral nerves.

Figure A: nerve regeneration through a high-transparency regenerative macro-sieve electrode. Figure B: nerve regeneration through a silicone nerve conduit. Figures C and D: epoxy nerve sections demonstrate numerous myelinated axons. (credit: Dan Moran, PhD, Washington University in St. Louis)

The ulnar nerve, one of three main nerves in the forearm, is the largest nerve in the body unprotected by muscle or bone and is connected to the ring finger and pinkie finger on the hand. It’s the nerve that is stimulated when you hit your elbow on something and trigger your “funny bone.” The median nerve in the upper arm and shoulder is connected to the other fingers on the hand, so together, the two nerves control movement and sensations including touch, pressure, vibration, heat, cold and pain in all of the fingers.

More control over prosthetic arms

Daniel Moran, PhD, professor of biomedical engineering in the School of Engineering & Applied Science and of neurobiology, of physical therapy and of neurological surgery at the School of Medicine, heads the project. People using arm prosthetics have to rely on their vision to use them properly, Moran says.

To pick up a cup of coffee, they have to be able to see the cup, place the fingers of the prosthesis around it and lift it. They are unable to feel whether the cup is in their hand, if the cup is hot or cold or if they are about to drop it. By enabling the ability to feel, users will have more control over the prosthesis.

DARPA is already funding the “Luke Arm,” a high-tech bionic limb created by DEKA Research. The prosthetic, named for “Star Wars” character Luke Skywalker, who received a prosthetic after losing his right hand in an epic battle with Darth Vader, is designed to help servicemen and women and veterans who had upper limb amputations. While the advanced prosthetic arm allows users to perform six different grips, such as picking up small objects, it does not provide users with the senses of touch and orientation of a natural hand.

Nearly 2 million people in the U.S. are living with the loss of a limb, including U.S. military veterans.