Magnetic sensors track muscle movement, for better prosthetic limb control.
MIT researchers showed that tiny magnets implanted in muscle can be tracked from outside the body to measure muscle movement in three people with below-knee amputations, which could improve prosthetic limb control.
Researchers at MIT report that they can accurately track muscle movement using small magnetic beads implanted in the muscle. The team says the measurements could make it easier for people with certain amputations to control prosthetic limbs. The findings appear in the journal Nature Sensors.
Neuroprosthetic limbs use signals from the muscles that remain after an amputation to guide the device. Until now, these devices have relied on electrodes placed on the skin, a method called electromyography. According to the researchers, those measurements have not been reliable enough to ensure safety while walking with a neuroprosthetic leg. The electrical signal fades when a muscle is held at one length for several seconds, electrodes can pick up signals from nearby muscles, and sweat can interfere.
The new approach is called magnetomicrometry. Pairs of magnets are implanted in a muscle, and sensors worn on the skin measure the change in distance between them as the muscle contracts or stretches. From that, muscle length and velocity can be calculated. The beads are 3 millimeters across, about the size of a sesame seed. They are made from neodymium, iron and boron, and are coated with gold and a polymer called parylene C to make them biocompatible. The signals can be read from up to 6 centimeters beneath the skin.
The study involved three participants with below-knee amputations. All had a surgical type that reconnects muscle pairs so they can still communicate within the residual limb. Magnets were implanted in up to four ankle muscles at Brigham and Women's Hospital. Electrodes were also implanted in the same muscles, so the team could compare magnetomicrometry, implanted-electrode electromyography and skin-surface electromyography.
Participants did not wear a prosthesis. Instead, they used their muscle movements to move a cursor to targets on a screen, a stand-in for controlling a robotic ankle-foot prosthesis. "Our results suggest that the magnet-based approach can offer more accurate and stable control," said Christopher Shallal, one of the study's lead authors.
The researchers are now running a larger study of how well people can control prosthetic limbs using the magnetic bead measurements. The work was funded in part by the Yang Tan Collective at MIT and a National Science Foundation Graduate Research Fellowship.
At a Glance
- The study appeared in Nature Sensors and involved three participants with below-knee amputations.
- The magnetic beads are 3 millimeters in diameter and can be read from up to 6 centimeters below the skin.
- Magnets were implanted in up to four ankle muscles, with surgeries performed at Brigham and Women's Hospital.
- A larger study of controlling prosthetic limbs with the magnetic measurements is now underway.
Sources
This brief was written by Brightside Report from the reporting linked above. Spot an error? Request a correction.