Magnetic beads track muscles for future prosthetic control
· BehindLines newsroom
Tracking a muscle's movement, rather than only its electrical activity, could improve prosthetic control. On 29 October, researchers described in Nature Sensors a system that detects small implanted magnets through the skin. The study involved three people with below-knee amputations and tested control of a virtual task.
Following the muscle's mechanics
The scientific abstract describes passive magnetic beads measuring 3 millimetres, tracked by sensors worn on the skin. The system monitors muscle movement in real time, with resolution finer than a millimetre at depths of up to 6 centimetres.
The authors report that their estimate of muscle state matched or exceeded electrical reference methods on most of the measures assessed. This comparison applies to these participants and tasks; it does not establish that the magnetic approach is always better.
In its account of the work, the Massachusetts Institute of Technology explains that changes in the distance between two magnets reveal both muscle length and the speed at which it moves.
An on-screen cursor, before evidence of walking
The experimental task is an essential distinction. MIT says participants were not wearing prostheses during the experiments: they used their muscles to guide a cursor towards a target.
All the volunteers had undergone a particular surgical procedure that reconnects pairs of muscles in the residual limb. They also had implanted electrodes, allowing magnetic signals to be compared with electrical measurements taken both inside the body and at the skin.
The findings represent a research step towards a control interface. They do not yet demonstrate that this system would let someone use an artificial leg safely in everyday life.
MIT says a larger study will assess control of actual prostheses. More natural movement therefore remains a goal to be tested; its account provides no timetable for commercial availability.