Magnetic Bead Implants Give Robotic Prosthetics Real Time Muscle Tracking
Researchers at MIT tracked muscle movements in three amputees using wireless magnetic sensors to improve neuroprosthetic control.
By Letizia Giugliano
2 min readHuman-Edited, AI-Assisted
Three human amputees have successfully tested an implantable magnetic tracking system that measures muscle movements in real time. The study from the Massachusetts Institute of Technology, published in the journal Nature Sensors, offers a new physical interface for robotics controllers that guide advanced prosthetic limbs.
Moving past four decades of skin electrodes
For forty years, neuroprosthetic control systems have relied on electromyography, a technique that uses surface electrodes on the skin to detect electrical signals in muscle tissue. That approach presents mechanical limits: electrical data does not directly convey position, torque, or resistance. Skin electrodes also suffer from signal drift when a muscle stays contracted, pick up cross-talk from adjacent muscles, and lose contact when sweat forms.
To overcome these issues, a team led by senior author and inventor Hugh Herr, professor of media arts and sciences and co-director of the K. Lisa Yang Center for Bionics at MIT, turned to a mechanical tracking method known as magnetomicrometry, as reported by MedicalXpress. The technique bypasses electrical proxies by directly measuring the physical length and velocity of muscle fibers, marking a notable innovation in bionic prosthetics.
“This interface is minimally invasive, so it could be accessible to more people. You place two beads in the muscle and you have access to all of this rich information about the muscle dynamics.”
— Christopher Shallal, MIT
Two magnetic beads to track muscle dynamics
The invention operates by placing pairs of miniature magnetic beads inside target muscle tissue. When the surrounding muscle contracts or stretches, external sensors mounted on the surface of the skin track changes in the magnetic field to calculate the exact distance between the two beads.
Co-lead author Christopher Shallal, a graduate researcher in the Harvard-MIT Program in Health Sciences and Technology, described the approach as a minimally invasive alternative to earlier methods. Because magnetic fields pass through biological tissue without wires, the sensor reads muscle mechanics directly through the skin. Co-lead author Cameron Taylor, assistant professor of biomedical engineering at the University of North Carolina at Chapel Hill, had previously verified the technique in animal models in 2021 before moving to human trials, according to MedicalXpress.
Cursor trials in patients with bionic limb surgery
The clinical trial evaluated the system in three participants with below-knee amputations who had previously undergone an agonist-antagonist myoneural interface procedure, known as AMI. During this surgery, opposing muscle pairs are surgically reconnected so that when one muscle contracts, its partner stretches dynamically.
During the study trials reported by MedicalXpress, participants did not wear a physical prototype limb. Instead, they moved their residual muscles to guide an on-screen cursor toward targets. The wireless tracking allowed the system to register continuous muscle dynamics, providing the kind of mechanical output data needed for robotics controllers to build a more natural gait.
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