“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 rather than 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 robots 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 person wearing the prosthesis often has little say in 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, a professor of media arts and sciences at MIT and the study’s principal investigator. and 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 were amputated below the knee through an approach known as 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 Harvard’s 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 muscles working in pairs. 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 lift the forearm up, while the triceps muscle is the antagonist because it activates the movement.
When surgery cuts off the severed muscle pairs, the patient’s ability to sense post-surgical muscle contractions is impaired, and this compromises 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.
The study is “part of a movement toward next-generation prosthetic technologies that will address not just movement, but also perception,” 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 disconnection In 2016, he became the first person since Jim Ewing to receive the procedure.
Patients with Ewing amputations experienced less muscle atrophy in their residual limb and less phantom pain—a feeling of discomfort in a limb.
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.
Amy Pietrafitta, a study participant in Ewing’s 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, Ewing amputees 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 with Ewing amputations and patients who received a new prosthesis were also 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.
