Swiss researchers have developed a prosthetic device designed with sensors in the sole of the foot that communicate more naturally with the brain and enable those with lower-limb amputations to feel the surface of the ground better when walking.
“The prosthesis feels more like a part of the body,” Stanisa Raspopovic, PhD, assistant professor at the Department of Health Sciences and Technology, ETH Zurich, told the Keystone-SDA news agency.
The new signal transmission was tested on three patients who were able to move faster and more safely. According Raspopovic, the test subjects were also able to concentrate on other things while walking, and they also made fewer mistakes when trying to spell words backwards while climbing stairs.
“Greater mobility is ultimately also good for health,” Raspopovic said.
Prostheses that are connected to the nervous system have been around for several years, however, according to Raspopovic, these lead to unpleasant sensations in patients, such as an annoying tingling sensation on the skin. “They send constant electrical pulsations. That’s not how our nervous system works,” he said.
Raspopovic’ and his team of researchers relied on biomimetic stimulation, signals that were modeled on nature. “We have learned the language of the nervous system, so to speak,” he said.
As a result, Natalija Katic, a PhD student in Raspopovic’s research group, developed a computer model called FootSim based on data that records the activity of special sensory cells in the sole of the foot. The model showed how the sensory cells in the soles of the feet behave during walking or running.
To test how well the model simulated the signals from the sole of the foot, researchers first implanted electrodes in cats on the leg nerve and spinal cord. When they applied pressure to the cat’s paw from below to generate the natural nerve activity during a cat’s step, the activity patterns recorded in the spinal cord resembled the patterns that occurred in the spinal cord after the researchers had stimulated the nerve in the leg with biomimetic signals.
In contrast, the conventional rigid stimulation produced a significantly different pattern in the spinal cord of the cats. According to Raspopovic, this shows that biomimetic stimulation is superior to conventional stimulation. The realization that nature-inspired signals work better than others is also important for other instruments, such as spinal implants or electrodes for brain stimulation, according to Raspopovic.
Editor’s note: This story was adapted from materials provided by ETH Zurich and Swissinfo.ch.
