An MIT-led team reported on October 29 in Nature Sensors that tiny magnetic beads implanted in muscle could accurately track muscle movement, a measurement approach the researchers suggest could support control of prosthetic limbs. The study involved three participants with below-knee amputations who received magnets in up to four muscles of the ankle joint, with surgeries performed at Brigham and Women's Hospital. The beads measured 3 millimeters in diameter, and the researchers said magnetic signals could be read from a depth of up to 6 centimeters.

In the experiments, participants were not wearing a prosthetic limb. They used muscle movements to move a cursor to targets on a screen, and the team compared magnet tracking with implanted and skin-surface electrode measurements. Senior author Hugh Herr said electrical activation alone cannot directly determine mechanical signals such as joint position, torque or impedance. The researchers said the results suggested the magnet-based approach offered more accurate and stable control.

According to the report, a larger study was underway to evaluate how well people could control prosthetic limbs using the magnetic bead measurements. The work was funded in part by the Yang Tan Collective at MIT, a National Science Foundation Graduate Research Fellowship and an MIT HEALS Graduate Fellowship.