Scientists have developed a prosthetic leg controlled by the human brain that could make it easier for amputees to walk up and down stairs.
The innovative new device allows patients to directly control their prosthesis using their thoughts.
The device records signals from surgically preserved muscles that are carefully monitored and converted into controls for a robotic ankle.
In a trial of 14 amputees, MIT researchers found that the leg created a more natural motion, improved stability on uneven terrain, and increased speed by 41%.
And researchers now expect a commercial version of the leg may not be available for as long as five years.
Study author Professor Hugh Herr said: ‘This is the first prosthetic study in history to show a prosthetic leg under full neural modulation, where a biomimetic gait emerges.
In their study, published in Nature Medicine, the researchers say their novel technique allows patients to receive “proprioceptive” feedback from the limb.
During trials, researchers found that this allowed patients to walk almost as fast as someone without an amputee and develop natural movements such as lifting their toes when climbing stairs.
This increased level of control is made possible by a new surgical amputation technique tested by researchers.
In traditional new applications, the muscles that normally control the foot are wrapped around the severed limb to create soft padding.
However, this process severs the normal connection between “antagonistic” pairs of muscles that push and pull in the leg.
MIT researchers have developed a new type of bionic leg that allows patients to control the limb directly with their thoughts.
Instead, the device requires patients to undergo a new form of below-knee amputation surgery called agonist-antagonist myoneural interface (AMI).
The ends of the muscles are connected together so that they can still communicate with each other within the residual limb.
During previous research, Professor Herr and his colleagues discovered that signals from these residual muscles could be used to replicate natural foot movements.
By registering the signals, the robotic ankle knows how far and with what force to bend and flex the foot so that the patient can control the limb naturally.
This process can be performed during the initial leg amputation or in a subsequent revision procedure; it can also be performed on the arms.
So far, only 60 people have undergone the procedure, but researchers hope it could pave the way for more natural bionic limbs.
The leg works by recording signals from surgically preserved muscles that are converted into instructions for the electronic ankle.
Lead author Hyungeun Song, a postdoctoral researcher at MIT, says: ‘Thanks to the AMI neuroprosthetic interface, we were able to boost that neural signaling, preserving as much of it as we could.
‘This was able to restore a person’s neural ability to continuously and directly control the entire gait, across different walking speeds, stairs, slopes, and even overcoming obstacles.’
Critically, the study also found that patients were more likely to say they felt their new prosthesis was part of their body.
The best prosthetics can help amputees regain their natural walking pattern through robotic sensors and predetermined gait algorithms.
However, these prostheses do not yet allow the patient to control their new robotic limb as if it were part of their original body.
Study author Professor Hugh Herr (pictured) says the technique allows patients to feel like the limb is part of their own body.
Professor Hare (pictured) hopes to achieve the goal of “rebuilding human bodies”, rather than allowing patients to control ever more advanced robotics.
Professor Herr says: ‘No one has been able to demonstrate this level of brain control that produces natural walking, where the human nervous system controls the movement, not a robotic control algorithm.
Professor Hare, who is a double amputee, says the problem with robotic prosthetics is that the patient does not feel the new limb is part of their body.
Although the patients received only 20 percent of the sensory feedback that a non-amputee would feel, they still developed natural walking habits as if it were a biological limb.
By allowing patients to directly control their limbs, Professor Hare hopes to achieve his goal of “rebuilding human bodies”.
He says: “The approach we are taking is to try to comprehensively connect the human brain with electromechanics.”
