If you were told ten years ago that prostheses would one day help people not only walk, but also... feel every single step, every single stone under your foot, would you have believed it? Yet today, in a cutting-edge laboratory, science is turning this fantasy into reality.
Imagine a world where prostheses are not just mechanical extensions of the body, but real sensory substitutes, capable of restoring the sensation of touch to those who have lost a part of themselves. We're getting there faster than we thought.
Prosthetics, a sensory revolution
The loss of a limb does not only result in the loss of its motor function, but also of its sensory function. And while traditional prostheses have offered a partial solution, restoring mobility, the sensation of touch has always remained an unfulfilled dream… until now.
The research, published on the pre-print server bioRxiv (I link it to you here), has unveiled a device that, by mimicking nerve activity, can be implanted in the remaining part of the leg, allowing amputees to “feel” as they walk. This not only improves their speed of movement, but also instills greater confidence in every step.
Elegant progress
Jacob George, a neuroengineer at the University of Utah, praised the study as “really elegant.” And it's not difficult to understand why. This research is not limited to a computational model, but extends to animal models and ultimately to humans. It is one of the first investigations conducted so comprehensively.
Many denture patients face unexpected challenges. Not being able to feel the pressure exerted on an object can lead to embarrassing situations, such as breaking or dropping objects – a lack of sensory feedback that has led some amputees to refuse the use of prosthetics. But, as they say, every problem is an opportunity in disguise.
A step forward. Literally.
In recent years, researchers have focused on prostheses that offer increasingly natural sensory feedback. Research from 2019 by George's team showed that biomimetic feedback allowed a patient to grasp fragile objects such as eggs and grapes with pinpoint accuracy. But how exactly does this feedback work?
In the new study, the researchers used a computer model to recreate how the nerves in the foot react to different stimuli, such as the perception of pressure. The goal was to create natural patterns of neural activity that might occur when you feel something with your foot or while walking.
Then the scientists used the model to deliver patterns of electrical impulses to peripheral nerves in the cats' paws, recording the activity of neurons in the spinal cord that receive input from those nerves. The result? A response similar to that of a real touch.
Man and prosthesis, a winning combination
The next step was to test the approach in humans. Three individuals with lower-limb amputations were fitted with prosthetics that include a sensor to record pressure information from the robotic foot during walking.
This device “feels” the sensations of walking and transmits this information to the amputee's nervous system, trying to imitate the sensations associated with walking.
Stanisa Raspopovich, a neuroengineer at ETH Zürich and co-author of the study, hopes that his team and others will continue to improve this technology. A more detailed understanding of how the nervous system detects and communicates different aspects of touch could help further refine such devices.
The ultimate goal? Feel everything again. It will be a magnificent journey.
