Scientists at MIT and Brigham and Women's Hospital have made a groundbreaking discovery in the field of prosthetics, creating a system that allows users to control their prosthetic legs using their own nervous systems. This innovative technology could revolutionise the lives of individuals with lower limb amputations, paving the way for a future where artificial limbs function seamlessly with the human body.
The key to this breakthrough is a new surgical procedure known as the agonist-antagonist myoneural interface (AMI). Unlike traditional amputation methods, AMI reconnects muscles in the residual limb, preserving the natural push-pull dynamics of muscle pairs. This seemingly simple change has a profound impact on the control and function of prosthetic limbs.
Dr. Hugh Herr, a professor at MIT and senior author of the study, explains the significance: "This is the first prosthetic study in history that shows a leg prosthesis under full neural modulation, where a biomimetic gait emerges. No one has been able to show this level of brain control that produces a natural gait, where the human's nervous system is controlling the movement, not a robotic control algorithm."
The AMI system provides users with proprioceptive feedback, the sense of where their limb is in space. This sensory information, often taken for granted by those with intact limbs, is crucial for natural movement. With the AMI, patients regain a portion of this vital feedback, enabling them to walk more naturally and confidently.
In the study, seven patients who underwent AMI surgery were compared to seven patients with traditional amputations. The results were remarkable. AMI patients walked faster, navigated obstacles more easily, and climbed stairs with greater agility. They also demonstrated more natural movements, like pointing their toes upwards when stepping over obstacles, a subtle yet important aspect of a natural gait.
The AMI system's adaptability is another impressive feature. Patients could adjust their gait to different real-world conditions, including walking on slopes and navigating stairs. This adaptability is crucial for everyday life where terrain and challenges can change quickly. In an obstacle-crossing trial, AMI patients demonstrated their ability to modify their gait effectively, showcasing the system's responsiveness to unexpected challenges.
The success of the AMI system relies on its ability to augment residual muscle afferents, the sensory signals sent from muscles to the nervous system. Even a modest increase in these signals can significantly improve control and function, highlighting the remarkable adaptability of the human nervous system.
Dr. Hyungeun Song, lead author of the study, states: "One of the main findings here is that a small increase in neural feedback from your amputated limb can restore significant bionic neural controllability, to a point where you allow people to directly neurally control the speed of walking, adapt to different terrain and avoid obstacles."
While this research represents a major advancement, it is just the beginning. The team at MIT is exploring ways to further enhance sensory feedback and improve the integration between the human nervous system and prosthetic devices. The AMI procedure has already been performed on about 60 patients worldwide, including those with arm amputations, suggesting broad applicability across different types of limb loss.
As this technology continues to evolve, we may see even more natural and intuitive control of artificial limbs. The ultimate goal is to create prosthetics that feel and function like a natural part of the user's body, blurring the line between human and machine.
This development marks a new era in bionics, offering hope for improved mobility, independence, and quality of life for millions of people living with limb loss. It also provides valuable insights into the plasticity of the human nervous system and our ability to integrate with advanced technology.