Magnetomicrometry

Magnetic sensors inside the muscles will allow you to control prosthetic limbs

Alexandra Medvedeva, Naked Science

Using a simple system of magnets, researchers from the Massachusetts Institute of Technology (USA) have invented a new way to track muscle movements. They have already proven the effectiveness of the technology in animal experiments and now plan to use this method to help people with amputations manage prosthetic limbs more accurately and naturally. The article was published in the journal Frontiers in Bioengineering and Biotechnology (Taylor et al., Untethered muscle tracking using magnetomicrometry).

Modern prosthetic limbs are usually monitored by electromyography (EMG). Electrodes attached to the skin surface or implanted into the residual muscle of an amputated limb measure signals from the muscles and transmit them to the prosthesis. However, this approach does not take into account any information about the length or speed of muscle contraction, which could make the movements of the prosthesis more accurate.

For several years, the authors of the article have been working on a new way of measuring muscle work. Their approach, dubbed "magnetomicrometry," uses permanent magnetic fields surrounding small balls implanted in the muscle.

A credit card-sized sensor attached to the surface of the body tracks the distances between two magnets. When the muscle contracts, the magnets come closer, and when it relaxes, they move away from each other.

Previously, scientists have shown that this system can be used to accurately measure small movements of the ankle. Now they have set a goal to find out whether the system can perform accurate measurements during natural movements outside of laboratory conditions. To do this, the researchers created an obstacle course for turkeys whose leg muscles were implanted with sensors. It turned out that during jumping, running and other movements, the system calculated the length of the muscles in less than a millisecond.

After that, the authors tested the biocompatibility of the implants. The magnets did not cause tissue scarring, inflammation or other undesirable side effects. In addition, the operation did not change the turkeys' gait, so probably the sensors did not provoke discomfort. In addition, the magnets remained stable for eight months, throughout the study, and did not migrate towards each other if they were implanted at a distance of at least three centimeters from each other.

Now scientists are planning to get approval to test the system on people with prosthetic limbs. They hope to use the sensor to control the prostheses in a similar way to how EMG is currently used. Magnetic sensors implanted into the preserved muscles of the limb will transmit information to the prosthesis about the degree of stretching of the muscle and give it the desired position.

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