Photograph courtesy of EPFL. Copyright Luca Rossina

Researchers have developed a next-generation prosthetic hand that allows people with amputations to regain proprioception. The results of the study, which were published February 20 in Science Robotics, are the culmination of ten years of robotics research. The prosthesis, developed by researchers from the École Polytechnique Fédérale de Lausanne, EPFL, Switzerland; the Sant’Anna School of Advanced Studies (SSSA), Pisa, Italy; and the A. Gemelli University Polyclinic in Rome, enabled its users to regain a very subtle, close-to-natural sense of touch, according to the researchers.

Recently, several research groups have been able to provide tactile feedback for people with prostheses, but Silvestro Micera, PhD, a professor at EPFL and SSSA, said that this latest study has taken things one step further.

“Our study shows that sensory substitution based on intraneural stimulation can deliver both position feedback and tactile feedback simultaneously and in real time,” he said. “The brain has no problem combining this information, and patients can process both types in real time with excellent results.”

The prosthesis allows patients to reach out for an object on a table and determine its consistency, shape, position, and size without having to look at it. It has been successfully tested on several patients and works by stimulating the nerves in the user’s residual limb. Current myoelectric prostheses allow people to regain voluntary motor control of their artificial limb by exploiting residual muscle function in the forearm, but because they lack sensory feedback require the user to rely on visual cues.

Intraneural stimulation of the new device re-establishes the flow of external information using electric pulses sent by electrodes inserted directly into the residual limb. Patients then undergo training to gradually learn how to translate those pulses into proprioceptive and tactile sensations.

The technique enabled two amputees to regain high proprioceptive acuity, with results comparable to those obtained in healthy subjects. The simultaneous delivery of position information and tactile feedback allowed the participants to determine the size and shape of four objects with a high level of accuracy (75.5 percent).

Editor’s note: This story was adapted from materials provided by École Polytechnique Fédérale de Lausanne.

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