Dennis Sørensen smiles confidently with his new robotic hand as he flexes his robotic fingers, and gingerly closes them around a disposable plastic cup. Sørensen is blindfolded but he 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 week long 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.