Building prosthetics that can feel

By

Scott Seckel

On May 27, 2011, Jason Little, a 41-year-old real estate investor from Orlando, Florida, was in an accident. His SUV rolled over on the interstate, shattering the driver’s side window. Little’s left arm was trapped outside, mangled beyond saving from the elbow down.

Flash-forward to this past summer, when he was matched with a prosthesis that connected to his nervous system. He hadn’t felt his wife’s touch with his left hand in more than seven years.

“I closed my eyes, she put her hand in the prosthetic, and I closed it, and I was able to tell her I was touching her hand,” Little said. “She broke down. It was a pretty powerful moment.”

The prosthetic hand, the first of its kind, is the culmination of 12 years of work by James Abbas (pictured above), an associate professor in the School of Biological and Health Systems Engineering at Arizona State University, and Professor Ranu Jung, chair of the Department of Biomedical Engineering at Florida International University. The research was announced last month.

“For someone to function in a more seamless way, if you’re at a dinner party or wherever, you want to pick up things without staring at them or paying a lot of attention,” said Abbas, director of the Center for Adaptive Neural Systems. “We feel there is value to this, maybe also in terms of returning to work.”

For Little, the value is incalculable. He can do things like open a water bottle without squeezing it too hard and bursting the bottle.

“It sounds like such a simple task, but when you don’t have that feedback, it’s very difficult to know how hard you’re squeezing something,” he said. “They’ve been able to get pretty close as far as where on my hand where I should feel things. It’s amazing."

Video courtesy of Florida International University 

With his old prosthesis, Little had to rely on visual or auditory cues that he was crushing something or letting it slip from his grasp.

“That’s the only feedback I was getting previously,” he said. “Now I can tell you whether an object is hard or soft. That’s incredible to me.”

Neural stimulation is not new. Researchers long have been interested in stimulating different areas of the brain to achieve various results, but there’s also interest in going into peripheral nerves, such as in the arms or legs.

Electrodes have been developed to go inside peripheral nerves. Fine wires, thinner than a human hair, are sewn into the nerve and activate neurons within small bundles of nerves called fascicles.

Ken Horch, professor emeritus of bioengineering at the University of Utah, has tested wires on amputees. People who hadn’t had a hand in 20 years could feel sensation, because, while the hand was gone, the appropriate nerves were still attached to the spinal column. The brain still thinks it’s feeling the hand. Abbas and Jung contacted Horch with the idea that the wire tech could be turned into a system someone could use on a daily basis.

They partnered with a medical device company called Cochlear Corporation. The company makes an electrode ear implant that is implanted in the inner ear structure. When the nerve fibers are stimulated, users can hear sound. About 300,000 people use cochlear implants.

“We worked with them to modify it for our needs,” Abbas said. “We were able to benefit from what Cochlear has already developed.”

What they created is called the Neural-Enabled Prosthetic Hand system. The wires are implanted in the upper arm. They connect to a neurostimulator implanted in Little’s shoulder that has a radio frequency coil and a magnet. When Little dons the arm, he positions an external coil over the implant and it is held in place with a magnet.

“It basically is sensing two things,” Abbas said. “One is the force on the thumb, and the other is how much it’s open.”

The hand opens and closes, and the thumb and forefinger “feel,” but not the other three fingers.

“If it gets too complex it’s going to be problematic,” Abbas said. “It just gives him more things to pay attention to. If you think about it, there are diminishing returns. … Right now there are just two pieces of information we’re trying to convey: How much is the hand open, and how much force is he applying?”

Part of the idea was to work with existing technology to get the arm out in the world sooner rather than later.

“If all goes well, we hope he’ll be using it for the rest of his life,” Abbas said.

To Little, the stimulation feels like being electrocuted, but at a one on a scale of 10.

“It’s a really weak electrocuting experience, is the best way to explain it,” he said. “It doesn’t hurt at all.”

He sends a signal from his brain to his muscle, and his muscle controls the hand. The prosthesis sends a sensation signal back.

“It’s two-way communication that’s brand-new,” he said. “With those two bits of information, I’ve been able to determine, with about 80 percent accuracy, whether I’m holding a block of wood or a block of foam, and whether or not that block is three-quarters of an inch wide, or an inch and a half wide, based on the hand position sensor.”

The project was funded by the Defense Advanced Research Projects Agency of the U.S. Department of Defense and the National Institutes of Health.

Top photo: Associate Professor James Abbas, director of the ASU Center for Adaptive Neural Systems, helped develop a neural-enabled prosthetic hand that allows its user to feel pressure and sense whether a held object is hard like a coffee mug or soft like a banana. The project has taken a dozen years to develop, and its electrodes were surgically implanted in the first subject, Jason Little of Orlando, in March 2018. Photo by Charlie Leight/ASU Now