Biohybrid robotic hands aim for a human touch.

WITH NO SENSATION OF TOUCH, hand prostheses are out of touch, failing amputees and others in need.

Enter a group of biomedical engineers in Florida and a physician in Utah who strive to tighten the wide functional gap between natural and artificial hands.

“Today’s prosthetic hands are only good at a single task at a time, whether it’s catching a ball or holding a golf club,” says Erik D. Engeberg, Ph.D., professor and mechanical engineer at Florida Atlantic University.

More complex actions requiring multiple moves — unlocking a door, using a remote control, playing a guitar—remain out of reach.

Such moves need feedback from physical sensation, which prosthetic hands can’t yet provide. Imagine wrapping a package, tying a hair ribbon or strumming guitar strings without being able to feel the ribbon or strings. So prosthetic upper limbs rely on users being trained to open their artificial hands with one set of forearm muscles (extensors) and close them with another (flexors). But alternating between the two can be as unnatural as trying to adjust your car’s outside mirrors with a toggle switch.

“If we can create a prosthetic that’s easier to control and has a sense of touch like a real hand, we can restore people’s function at a higher level,” Engeberg says. “For a violinist or athlete, restoring higher function would make a huge difference in their quality of life. Getting an artificial hand that works as well as a human hand is the holy grail.”

That’s why Engeberg has devoted his career—and more than 17 years thus far—to that quest.

Living neurons are key

Engeberg’s team of biomedical engineers, an orthopedic physician and researchers have made bold moves departing from the technique of embedding sensorydevices in patients’ brains, which is invasive, expensive and highly regulated.

Instead, he’s found a way to grow living neurons in vitro and use them to transmit the needed electrophysiological signals that intuitively translate thought into action for dexterous robotic hands. His have 25 touch receptors in each fingertip—versus thousands in a real fingertip.

Those sensors contain microelectrodes through which electric currents run, recreating the communication between muscles and peripheral nerves emanating from the spinal cord, a link that’s essential to movement.

“His approach of experiments in the lab instead of on people is totally different and has great potential to reach the goal faster than other research being done,” says Douglas T. Hutchinson, M.D., the current project’s medical adviser and an orthopedics professor at University of Utah in Salt Lake City.

“Not many people want experiments on their partially amputated arms,” says Hutchinson, who implanted the electrodes for the related research that was the underpinning of Engeberg’s Ph.D. thesis on hand prosthetics at University of Utah in 2007.

Engeberg credits Hutchinson with providing “clinical insights to make the research platform as realistic as possible.”

Already, “the fingertips can tell the difference between an orange peel and a banana peel,” he says. “Those sensations are mapped by your brain and delivered by electric activity through nerves. You touch something and take an action based on the sensation.”

Engeberg hopes to create prostheses that can detect friction, moisture, pain and temperature via tactile sensors.

More challenges must be faced

To reach the goal of an artificial hand that rivals a natural one, much remains to be done.

One hurdle is that training robotic hands in new skills is slow. “A robotic hand can be taught to play one song very well, but that’s all it can do,” Engeberg says. “Teaching it a new task is very challenging, so while a robotic prosthesis can type or play piano, it’s not at the same level as a human hand.”

Change is on the horizon

Still, biohybrid robotic hands will be a “game-changer,” Hutchinson says.

“There’s a huge advantage to this kind of prosthesis,” Hutchinson says. “A prosthetic hand has to act as the amputee wants and has to feel like part of their body.”

“A lot more must be done,” he says. “But Engeberg has done a great job at moving research forward.” •