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Leg Prosthetic System Restores Sensory Feedback

Walking with prosthetic device

Volunteer walking with sensory-enabled prosthetic device (ETH Zurich)

3 Oct. 2019. Results from a small clinical trial shows a system for leg prosthetic devices restores tactile sensory feedback to improve mobility and reduce falling. Researchers from ETH Zürich and École Polytechnique Fédérale de Lausanne, or EPFL, in Switzerland report their findings in yesterday’s issue of the journal Science Translational Medicine (paid subscription required).

People wearing a prosthetic device after a leg amputation must deal with a lack of haptic feedback or sense of feeling when wearing the device. As a result, users’ mobility is limited and they face a higher risk of falling, which are often reasons for abandoning the device. Researchers from the neuroengineering lab of robotics professor Stanisa Raspopovic at ETH Zürich designed a system that adds sensory feedback in real time to a lower-leg prosthetic device, making it feel like more a natural part of the user than an external object.

A team led by postdoctoral researcher Francesco Petrini designed a system that adds sensors at key points in a prosthetic device for people needing an amputation above the knee. The sensors measure pressure and balance in the insole, along with flexing at the knee. Readings from the sensors are sent via Bluetooth to a controller, then relayed to a stimulator with electrodes connected to the sciatic nerve. Petrini and colleagues from ETH Zürich, EPFL, and a spin-off company SensArs Neuroprosthetics in Lausanne, designed the sensory feedback system to fit in and work with prosthetic devices now on the market.

The researchers, with associates in Belgrade, Serbia, recruited three volunteers with amputations above the knee to test the device. The team first asked the volunteers to report a sense of feeling in the prosthetic device at multiple points in the foot and lower leg, as well as flexing sensation in the knee. In addition, the researchers asked participants to report the position of their limbs, a sensory condition known as proprioception. Tests were conducted with connections for the sensors turned off and on, and participants reporting far more sensations with the connections on than off.

The researchers then asked the volunteers to perform more complex tasks. Participants climbed and descended stairs, and navigated an obstacle course, with the speed of executing these tasks and number of times they lost balance or fell recorded. The team also tested for agility, asking participants to step one foot in front of the other on a line printed on the floor. The three participants performed all of these tasks faster and with greater ease with the sensor connections turned on than off. In addition, the participants exerted less cognitive effort with the sensory system turned on in their prosthetic devices, and considered the sensory-enabled prosthesis more a part of their bodies.

SensArs Neuroprosthetics is commercializing the technology. The company is developing a system called Sensy that the company says restores feeling for people with amputations. In February 2019, Science & Enterprise reported on a system to provide people with prosthetic hands and arms a better sense of the position of their limbs, by the many of the same authors involved with SensArs Neuroprosthetics.

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