“We were able to show the first fully neural control of bionic walking,” said Hyunkyun Chang, the study’s first author and a postdoctoral researcher at MIT.
Most advanced bionic prosthetics rely on preprogrammed robotic commands instead of the user’s brain signals. Advanced robotic technologies can sense the environment and repeatedly execute predefined leg movements to help a person navigate that type of terrain.
But many of these robotics work best on uneven surfaces and struggle to navigate common obstacles like bumps or puddles. When the prosthesis is in motion, especially in response to sudden terrain changes, the prosthesis wearer often has little to say when adjusting the prosthesis.
“When I walk, an algorithm sends commands to a motor, so it feels like I’m walking, but I’m not,” said Hugh Herr, the study’s principal investigator and a professor of media arts and sciences at MIT. A pioneer in the field of biomechatronics, a field that combines biology with electronics and mechanics. Herr’s legs were amputated below the knee due to frostbite several years ago, and he uses advanced robotic prosthetics.
“There is mounting evidence [showing] “When you connect the brain to a mechatronic prosthesis, a metaphor occurs where a person views the prosthetic limb as a natural extension of their body,” Herr said.
The authors worked with 14 study participants, half of whom had below-the-knee amputations through an approach called agonist-antagonist myoneural interface – AMI, while the other half underwent traditional amputations.
“What’s really cool about this is how it’s improving surgical innovation with technological innovation,” said Conor Walsh, a professor at the Harvard School of Engineering and Applied Sciences who specializes in developing wearable assistive robots and was not involved in the study.
AMI amputation was developed to address the limitations of traditional amputation surgery, which cuts critical muscle attachments at the amputation site.
Movements are made possible by moving in pairs of muscles. One muscle – known as the agonist – contracts to move a joint and the other – known as the antagonist – lengthens in response. For example, during a biceps curl, the biceps muscle is the agonist because it contracts to raise the forearm up, while the triceps muscle is the antagonist because it activates the movement.
When surgery severs the amputated muscle pairs, the patient’s ability to sense post-surgical muscle contractions is impaired, thereby compromising their ability to accurately and well sense where their prosthesis is in space.
In contrast, the AMI procedure reattachs the muscles in the remaining joint.
“This study is part of a movement toward next-generation synthetic technologies,” said Eric Rombokas, assistant professor of mechanical engineering at the University of Washington, who was not involved in the study.
A below-knee amputation is called an AMI procedure Ewing amputation In 2016, he became the first person since Jim Ewing to receive the procedure.
Patients who underwent Ewing amputations experienced less muscle wasting in their surviving limbs and less phantom pain, the sensation of experiencing discomfort in a limb that no longer exists.
The researchers fit all participants with a novel bionic joint, which consists of an artificial ankle, a device that measures muscle movement and electrical activity from electrodes placed on the surface of the skin.
The brain sends electrical impulses to the muscles, causing them to contract. The contractions generate their own electrical signals, which are detected by electrodes and sent to tiny computers inside the prosthesis. Computers convert those electrical signals into power and motion for the satellite.
Study participant Amy Pietrafitta, who received an Ewing amputation after severe burns, said the bionic joint gave her the ability to point both legs and perform dance moves again.
“It’s very real to have that type of flexibility,” Pietrafitta said. “It felt like everything was there.”
With their enhanced muscle senses, participants with Ewing amputations were able to use their bionic limbs to walk faster and with a more natural gait than traditional amputees.
When a person has to deviate from normal walking patterns, they may have to work harder to get around.
“That energy expenditure … makes our heart work harder and our lungs work harder … and it can lead to gradual destruction of our hip joints or our lower spine,” says Matthew J., a reconstructive plastic surgeon at Brigham and Women’s Hospital. Cardi said. and was the first physician to perform the AMI procedure.
Patients who received an Ewing amputation and a new prosthesis were able to navigate ramps and stairs with ease. They steadily adjusted their feet to push themselves off the stairs and absorb the shock of the descent.
The researchers hope to have the novel prosthesis commercially available within the next five years.
“We’re starting to get a glimpse of this glorified future where a person can lose a large part of their body and have the technology to reconstruct that aspect of their body to full function,” Herr said.
