Djurica Resanovic lost his leg in a motorcycle accident several years ago, resulting in him having an amputation above the knee. But thanks to neuroprosthetic leg technology, he was successfully merged with his bionic leg during clinical trials in Belgrade, Serbia.
“After all of these years, I could feel my leg and my foot again as if it were my own leg,” he said of the bionic leg prototype. “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.”
Scientists from a European consortium, led by Swiss education institutions ETH Zurich and EPFL spin-off SensArs Neuroprosthetics, implemented the bionic leg technology in collaboration with Serbian institutions. The results were reported in Science Translational Medicine journal.
“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,” explained lead author Dr Stanisa Raspopovic, an ETH Zurich professor and co-founder of SensArs Neuroprosthetics.
He added: “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.”
Wearing a blindfold and earplugs, Resanovic could feel his bionic leg prototype, thanks to sensory information that was delivered wirelessly via electrodes surgically placed into his leg 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 co-author Dr Silvestro Micera, EPFL’s Bertarelli Foundation Chair in Translational Neuroengineering, professor of bioelectronics at Scuola Superiore Sant’Anna, and co-founder of SensArs Neuroprosthetics.
“We believe intraneural electrodes are key for delivering bio-compatible information to the nervous system for a vast number of neuroprosthetic applications. Translation to the market is just around the corner,” said Micera.
Resanovic 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.”
He and two other leg amputees, all with transfemoral amputation, had participated in the three-month clinical study to test the new bionic leg technology, which literally takes neuroengineering a step forward, providing a promising new solution for this highly disabling condition that affects more than four million people in Europe and the US.
Thanks to detailed sensations from the sole of the artificial foot and 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 preoccupied with the bionic leg, leaving more mental capacity available to successfully complete the various tasks.
These results complement a recent study that demonstrated the clinical benefits of the bionic technology, like reducing phantom limb pain and fatigue.
The fundamental neuroengineering principle is about merging body and machine. It 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 biosignals that are delivered into the stump’s nervous system, into the tibial nerve via intraneural electrodes, and to the brain for interpretation.
“We developed the sensory feedback technology to augment prosthetic devices,” explained Francesco Petrini, CEO and co-founder of SensArs Neuroprosthetics, who is guiding an effort to bring these technologies to market.
“An investigation longer than three months, with more subjects and with in-home assessment, should be executed to provide more robust data to draw clinically significant conclusions about an improvement of the health and quality of life of patients.”
This project was funded in part by the NCCR Robotics and the Bertarelli Foundation.