February 11, 2014

Bionic Hand Provides Real-Time Sensory Perception

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Sørensen could grasp objects intuitively and identify what he was touching while blindfolded. Photograph courtesy of the Lifehand 2 consortium and Università Campus Bio-Medico di Roma.

A group of scientists from Switzerland, Italy, and Denmark have reported on the results of their study in which a man was able to achieve real-time bidirectional sensory feedback with a bionic prosthetic hand that was wired to nerves in his residual upper arm. Silvestro Micera, PhD, an associate professor of neuroprosthetics at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, and colleagues at EPFL and Scuola Superiore Sant’Anna (SSSA), Pisa, Italy, developed the sensory feedback system. The results were published online February 5, in the journal Science Translational Medicine, and represent a collaboration called Lifehand 2 between several European universities and hospitals.

Dennis Aabo Sørensen, 36, from Denmark lost his left hand in a fireworks-related accident nine years ago. On January 26, 2013, he underwent surgery at Policlinico Universitario Agostino Gemelli (Gemelli), Rome, Italy. A specialized group of surgeons and neurologists implanted electrodes into the ulnar and median nerves of Sørensen’s left arm. After 19 days of preliminary tests, Micera and his team connected a bionic prosthesis to the electrodes—and to Sørensen—every day for an entire week. A prototype of this technology was tested in February 2013 during a clinical trial.

The researchers were initially worried about reduced sensitivity in Sørensen’s nerves since they hadn’t been used in more than nine years, but they say these concerns faded away as the scientists successfully reactivated Sørensen’s sense of touch.

“The sensory feedback was incredible,” said Sørensen. “I could feel things that I hadn’t been able to feel in over nine years.” In a laboratory setting wearing a blindfold and earplugs, Sørensen was able to detect how strongly he was grasping, as well as the shape and consistency of different objects he picked up with his prosthesis. “When I held an object, I could feel if it was soft or hard, round or square.”

Micera and his team enhanced the prosthetic hand they used with sensors that detect information about touch. This was done by measuring the tension in artificial tendons that control finger movement and turning this measurement into an electrical current. But this electrical signal is too coarse to be understood by the nervous system. Using computer algorithms, the scientists transformed the electrical signal into an impulse that sensory nerves can interpret. The sense of touch was achieved by sending the digitally refined signal through wires into four electrodes that were surgically implanted into what remains of Sørensen’s upper arm nerves.

The ultra-thin, ultra-precise electrodes were developed by microsystems engineer Thomas Stieglitz, MSEE, PhD, and his research group at Albert-Ludwigs-Universität Freiburg, Germany. The electrodes made it possible to relay extremely weak electrical signals directly into the nervous system. A tremendous amount of preliminary research was done to ensure that the electrodes would continue to work even after the formation of post-surgery scar tissue. It is also the first time that such electrodes have been transversally implanted into the peripheral nervous system of an individual with an amputation.

The clinical study provides the first step toward a bionic hand, although a sensory-enhanced prosthesis is years away from being commercially available. The next step involves miniaturizing the sensory feedback electronics for a portable prosthesis. In addition, the scientists will fine-tune the sensory technology for better touch resolution and increased awareness about the angular movement of fingers.

The electrodes were removed from Sørensen’s arm after one month due to safety restrictions imposed on clinical trials, although the scientists are optimistic that they could remain implanted and functional without damage to the nervous system for many years.

Editor’s note: This story was adapted from materials provided by EPFL.

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