A pioneering study published in Nature Medicine unveils a groundbreaking development in prosthetic technology, enabling a select group of patients with below-the-knee amputations to control their prosthetic legs using neural signals. This advancement marks a significant departure from traditional prosthetic control methods, where movements are typically pre-programmed.
Led by Hugh Herr from the MIT Media Lab, the study introduces the concept of an agonist-antagonist myoneural interface (AMI), achieved through specialized amputation surgery and a non-invasive surface electrode connection to the robotic prosthetic lower leg. This interface establishes a bidirectional link between the wearer’s body and the artificial limb, enhancing control and proprioception—the awareness of the limb’s position in space.
Herr explains, “The patients that have this neural interface are able to walk at normal speeds; and up and down steps and slopes; and maneuver obstacles really without thinking about it. It’s natural. It’s involuntary.”
The AMI surgery involves connecting pairs of muscles and integrating synthetic elements to enhance the interface’s functionality. Muscle-sensing electrodes transmit signals to a small computer in the prosthetic limb, interpreting them into precise movements for ankle and foot joints. In return, feedback about the leg’s position aids in restoring a natural sense of movement.
According to Daniel Ferris, a neuromechanical engineer not involved in the study, “It’s a really novel idea that they’ve built on over the last eight years that’s showing really positive outcomes for better bionic lower legs.”
Testing involved tasks like walking on various terrains and navigating obstacles, where AMI users demonstrated a significantly more natural gait compared to those using conventional prosthetics. This naturalistic motion not only improves mobility over challenging surfaces but also reduces physical strain and potentially enhances social interaction for amputees.
The efficiency of the AMI interface is highlighted by its ability to transmit essential information using only 18 percent of the typical neural output from a limb to the spine, yet achieving results comparable to a natural gait.
AMI surgeries have now become standard at Brigham and Women’s Hospital in Massachusetts, indicating potential widespread adoption due to improved patient comfort and functional outcomes. With commercialization efforts underway, Herr envisions neural integration as the next frontier, aiming for prosthetics to be perceived not just as tools but as integrated parts of the body.
As the field progresses, the focus remains on refining the connection between amputation sites and prosthetic devices, with commercial viability potentially within the next five years. This transformative research not only promises enhanced mobility for amputees but also sets a new standard in prosthetic technology, paving the way for future advancements in neural-controlled bionic limbs.
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