While a number of groups are developing thought-controlled prosthetic hands, most of the devices require electrodes or other relatively fiddly electronics to be implanted in the amputee's body. Such is not the case with a new system, however, which works with tiny inert implanted magnets.
For most thought-controlled prosthetic hands, electrodes are implanted in the user's residual arm stump, or even in the brain.
As that person thinks about moving the fingers of the hand in a given fashion, those electrodes detect the nerve signals that travel from the brain towards the hand. Integrated electronics translate those signals into commands that are relayed to the hand's servos, causing the fingers to move as desired.
Led by Prof. Christian Cipriani, scientists at Italy's Scuola Superiore Sant'Anna (Sant'Anna School of Advanced Studies) set out to develop a simpler yet better-performing alternative. The resulting system was trialled on a 34-year-old test subject named Daniel, who lost his left hand in an accident in September of 2022.
Utilizing MRI scans and electromyography (the monitoring of electrical activity in muscle tissue), the scientists started by determining how the muscles in Daniel's left arm stump contracted when he thought about moving the fingers of his missing hand. Part of what made Daniel a good recipient was the fact that he was already experiencing phantom limb sensation, a common phenomenon in which amputees still feel the presence of a missing limb.
Based on their observations, the researchers implanted six small magnets – each just a few millimeters in size – into some of the key muscles. They then fitted Daniel with a Mia-Hand prosthetic hand, which included a carbon fiber cuff that was worn over his arm stump.
As the muscles in that arm contracted in response to his finger-movement thoughts, magnetic field sensors in the cuff detected the corresponding movements of the implanted magnets. Depending on which magnets/muscles were moving in which way, the fingers of the hand were prompted to move in the associated fashion.
In tests performed so far, Daniel has used the hand to perform tasks such as opening a jar, using a screwdriver, closing a zip-lock bag, cutting with a knife, plus picking up and moving various objects. He was also able to modulate his grasping force when handling fragile items.
"The trial on the first patient was successful," says Cipriani. "We are ready to extend these results to a broader range of amputations."
A paper on the study, which is part of the European Research Council's MYTI project, was recently published in the journal Science Robotics. Daniel can be seen using the hand, in the video below.
Scientist at MIT are developing a similar system, in which prostheses are controlled by implanted magnetic beads.
