Sesame-seed magnets could make prosthetic limbs move naturally

MIT researchers can now track muscle movement using magnetic beads the size of a sesame seed, a step toward prosthetic limbs that move more like the real thing. The study, published this week in Nature Sensors, implanted tiny magnets into the ankle muscles of three people with below-knee amputations. When a muscle contracts, external sensors measure the shifting distance between the beads, revealing muscle length and speed. For four decades, prosthetics have relied on skin electrodes, which fade when a muscle holds still and get confused by sweat. The magnetic version, tracked wirelessly through the body, proved more accurate and stable. "You place two beads in the muscle and you have access to all of this rich information about the muscle dynamics," said graduate student Christopher Shallal. The surgeries happened at Brigham and Women's Hospital. For now, participants used their muscles to move a cursor on a screen. The ankle comes next.