To move a prosthetic limb, electrical signals from the muscles are typically translated into the desired motion. Current technology commonly measures the signals via electrodes that are either on the skin or implanted through an invasive surgical procedure, and it often requires wires to connect to a power supply. A team from the BioRobotics Institute of the Sant’Anna School of Advanced Studies in Italy has skipped over the electrical signal and built an artificial hand that responds to muscle contractions in a user’s arm.
Led by Christian Cipriani, the researchers designed the prosthetic hand for people whose limb was amputated recently enough that the surrounding arm muscles still respond to signals from the brain. The hand is attached to a sleeve that wraps around the user’s arm.
A recent amputee last year trialed the new prosthesis for six weeks. Making incisions smaller than 2 cm, the team surgically implanted six permanent magnets into the person’s arm muscles. Subtle shifts in the magnets’ positions when the muscles contracted would alter the magnetic field that was monitored by sensors in the sleeve portion of the artificial limb. After initial calibration, the user was able to move the artificial hand as if it were his own. He could perform daily tasks, including tying shoelaces, cutting food with a knife, and opening jars.
The study is the first clinical implementation of a hand prosthesis controlled by muscle movements in real time. The magnetically guided hand demonstrated similar levels of dexterity and control to other commercially available prostheses. Finger motion was precise, and the technology reliably translated the amount of muscle contraction to the intended force. The artificial limb is also self-contained: The implanted magnets do not require power, and the sleeve contains all the hardware components, including a rechargeable battery, to interpret the magnetic field changes and move the hand in response.
The researchers did run into challenges. They had to implement a filter in the software to ignore unwanted hand movement commands concurrent with elbow movement, which had changed the position of the magnets and thus the control signal. Work is being done to mitigate the issue. Future tests will involve implanting the magnets deeper in the muscle tissue to capture larger and more precise movements. The BioRobotics Institute has secured funding to pursue the technique for a broader range of prosthetic limbs. (M. Gherardini et al., Sci. Robot. 9, eadp3260, 2024.)
