LifeHand2

Dennis Sørensen smiles confidently as he

flexes his robotic fingers, and gingerly closes them around a disposable plastic cup. Although blindfolded, Sørensen instantly recognizes what he is touching. Round. Hard. Breakable. Lethargic sensory nerves, rusty and unused since an accident nine years ago, begin to stir.

Scientists have been hacking into the nervous system for decades, determined to hot-wire the brain to build more intuitive prostheses. They've come so far they can build robotic limbs that users control with their minds. The next frontier is feedback: Prostheses that send signals to the body and brain. In a study just published in Science Translational Medicine, researchers say that they have developed a prosthetic hand that can feel texture, respond to pressure, and restore an amputee's lost sense of touch.

"We were able to delivery sensory information, and [Sørensen] was able to use that information in real time," says Silvestro Micera, a bioengineer at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and the Scuola Superiore Sant'Anna (SSSA) in Italy, and coauthor on the study.

Connecting Biology to Machinery

The peripheral nervous system is a natural circuit board, a complex web of nerves and tissue that translates electrical signals into sensations. Even after his accident, Sørensen's nervous system remained largely intact, giving Micera and his team the opportunity to tap into their patient's biological circuitry.

Sørensen volunteered to undergo a surgical procedure in which a team of neurologists and engineers implanted electrodes directly into the nerves in his upper arm. "You need surgery to access the peripheral nerves," Micera says. "The surgery is not that complicated and, in general, we are provoking very insignificant damage to the nerve."

The researchers developed a novel robotic hand that expressed small pressure changes in its artificial tendons as an electrical current. Micera and his team then attenuated the hand's coarse electrical signals into fine impulses that could interface with Sørensen's body. During a weeklong clinical study, Sørensen sat at a table, blindfolded, as information flowed electronically from a robotic hand to his nervous system.

Sørensen's current, commercial prosthesis clamps down on objects in response to muscle movements in his upper arm. But without sensory feedback, he must carefully avoid crushing the objects that he holds. As researchers passed cups, napkins and other household items to Sørensen's new robotic hand, he confirmed that he could feel an object's consistency and shape, and determine whether he was squeezing too tightly.

Struggle for Sensation

Micera's team is not the first to produce a prosthetic hand that provides direct feedback to the patient. Dustin Tyler, a professor at Case Western Reserve University in Ohio, recently produced a video of a bionic hand he made that was so sensitive that it allowed an amputee to grasp a cherry and remove its stem without crushing the fruit. While Tyler believes that Micera's robotic hand is a step in the right direction, he questions just how much the patient could actually feel.

"The study has done a good job of showing the value of direct neural interfaces for control of grasp in a prosthetic device," Tyler says. "But the paper doesn't actually quantify sensation very much. Making a hand that can actually feel is going to depend on a better quantification of what is actually felt. The hand is getting realistic feedback, yes, but is it a hand that can feel?"

Tyler's concern is justified. Although the prosthesis prevented Sørensen from crushing objects and lent him a general impression of what he was touching, the study describes his actual experience only subjectively. "When I held an object, I could feel if it was soft or hard, round or square," Sørensen said in a press release. But just how close Sørensen's prosthesis comes to mimicking the sensation in a human hand remains to be quantified.

The Bionic Future

Micera maintains that his robotic hand represents a major step forward in prosthetic technology. "Our patient was able to feel the amount of force when grasping," Micera says. "We've gone from "I'm touching or I'm not touching' to "how much am I touching, how much force am I producing.'"

The next hurdle for Micera will be to scale down the prosthesis so that the electronics and computer can be implanted inside the patient's body. "In our study, the electronics and the computer were outside on a table," he says. "The next step will be to make everything implanted, similar to a pacemaker," which he predicts will be possible in two to three years.

Tyler cautions that because Micera's study was but a weeklong glance at a prosthesis, the long-term durability of his robotic hand remains to be seen. "The next step will be to show that the interface will last the lifetime of the individual," Tyler says.

But for thousands of amputees, this technology could mean more interactive prostheses that come closer than ever before to restoring normal function. "With a sense of touch, you can grasp fragile objects and shake hands," Micera says. "The prosthesis can become part of your own body."

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