Thanks to specially bio-engineered electrical signals mimicking sensory information from the missing limb, the neuroprosthetic leg tried with three different amputees gave them full proprioception, not only restoring a natural gait but also enabling them to climb over various obstacles without having to look.
The fundamental neuroengineering principle involves imitating the electrical signals that the nervous system would have normally received from the person’s own, real leg. Specifically, the bionic leg prototype is equipped with seven sensors all along the sole of the foot and one encoder at the knee that detects the angle of flexion. These sensors generate information about touch and movement from the prosthesis.
Next, the raw signals are engineered via a smart algorithm into bio-signals which are delivered into the stump’s nervous system, into the tibial nerve via wirelessly connected intra-neural electrodes, and these signals reach the brain for interpretation.
One of the amputees, Djurica Resanovic, lost his leg in a motorbike accident several years ago which resulted in amputation above the knee. Giving his impressions about the bionic leg prototype, Resanovic said he could feel his leg and foot again, as if it were his own leg.
“It was very interesting. You don’t need to concentrate to walk, you can just look forward and step. You don’t need to look at where your leg is to avoid falling” he said. “I could tell when they touched the big toe, the heel, or anywhere else on the foot. I could even tell how much the knee was flexed.”
“We showed that less mental effort is needed to control the bionic leg because the amputee feels as though their prosthetic limb belongs to their own body,” explains Stanisa Raspopovic, ETH Zurich professor and co-founder of EPFL spin-off SensArs Neuroprosthetics, who led the study.
“This is the first prosthesis in the world for above-knee leg amputees equipped with sensory feedback. We show that the feedback is crucial for relieving the mental burden of wearing a prosthetic limb which, in turn, leads to improved performance and ease of use.”
The bionic leg prototype delivers sensory information to the amputee wirelessly, via electrodes surgically placed into the stump’s intact nervous system. These electrodes pierce through the intact tibial nerve instead of wrapping around it. This approach has already proven to be efficient for studies of the bionic hand led by Silvestro Micera, co-author of the publication, EPFL’s Bertarelli Foundation Chair in Translational Neuroengineering, professor of Bioelectronics at Scuola Superiore Sant’Anna, and co-founder of SensArs Neuroprosthetics.
Thanks to detailed sensations from the sole of the artificial foot and from the artificial knee, all three patients could manoeuvre through obstacles without the burden of looking at their artificial limb as they walked. They could stumble over objects yet mitigate falling. Most importantly, brain imaging and psychophysical tests confirmed that the brain is less solicited with the bionic leg, leaving more mental capacity available to successfully complete the various tasks.
The findings were reported in a paper titled “Enhancing functional abilities and cognitive integration of the lower limb prosthesis” in Science Translational Medicine.
The sensorized sole coupled to the prosthetic leg was developed by SensArs, spun-off from NCCR Robotics in 2016.
NCCR Robotics – www.nccr-robotics.ch
SensArs Neuroprosthetics – www.sensars.com