MIT team uses magnets the size of sesame seeds to read muscles for robotic legs
Tested in three people with below-knee amputations, the method could give prosthetic limbs more natural control.
Researchers at the Massachusetts Institute of Technology said Oct. 29 that tiny magnets placed inside muscles can track muscle movement well enough to help steer robotic prosthetic legs.
Today, many powered prosthetics read the electrical signals muscles give off, using electrodes stuck to the skin. MIT said those readings can fade when a muscle is held still, pick up the wrong muscle or be thrown off by sweat.
In the new method, two magnetic beads go into a muscle. Each is 3 millimeters wide, about the size of a sesame seed, and coated in gold and a plastic film so the body tolerates it. A sensor worn over the skin tracks the beads wirelessly from as deep as 6 centimeters, about 2.4 inches. As the muscle stretches and tightens, the beads move closer or farther apart. That gap shows the muscle's length and speed, which tells a robotic leg how the person wants to move.
Because the beads are so small and are tracked without wires, the method is less invasive than the implanted electrodes Herr's team used in an earlier robotic knee, MIT said. "This interface is minimally invasive, so it could be accessible to more people," said Christopher Shallal, an MIT graduate student and a lead author.
The team tested the beads in three people with below-knee amputations. In a computer task, the magnets gave more accurate and steadier control than skin electrodes, MIT said. A larger study with real prosthetic legs is underway. The study appears in the journal Nature Sensors and comes from the lab of MIT professor Hugh Herr.