A research team from the Scuola Superiore Sant’Anna has developed the first prosthesis with magnetic control, a new way of controlling the movements of a robotic hand. The magnetically controlled prosthetic hand allows users to reproduce all movements simply by thinking and to control the force applied when grasping fragile objects. There are no wires or electrical connection, only magnets and muscles to control the movements of the fingers and enable everyday activities such as opening a jar, using a screwdriver, or picking up a coin.
“The trial on the first patient was successful. We are ready to extend these results to a broader range of amputations,” said Christian Cipriani, director of the BioRobotics Institute of the Scuola Superiore Sant’Anna and head of the artificial hands area.
A research team from the BioRobotics Institute developed the new interface between the user’s residual limb and the robotic hand to decode motor intentions. The system involves implanting small magnets into the muscles of the forearm. The implant, integrated with the Mia-Hand robotic hand developed by the spin-off Prensilia, was successfully tested on the first patient who used the prosthesis for six weeks.
Myokinetic control, the decoding of motor intentions by means of implantable magnets in the muscles, is the latest frontier explored by the research team. The idea behind the new interface is to use small magnets, a few millimeters in size, to be implanted in the residual muscles of the residual limb and use the movement resulting from muscle contraction to open and close the fingers.
“There are 20 muscles in the forearm and many of them control the hand movements. Many people who have lost a hand keep on feeling it as if it is still in place and the residual muscles move in response to the commands from the brain,” Cipriani said.
The research team mapped the movements and translated them into signals to guide the fingers of the robotic hand. The magnets have a natural magnetic field that can be easily localized in space. When the muscle contracts, the magnet moves, and a special algorithm translates this change into a specific command for the robotic hand.
In April 2023, the participant, Daniel, 34, underwent surgery to implant six magnets in his arm. He was selected as a volunteer for the study because he still felt the presence of his hand and the residual muscles in his arm responded to his movement intentions.
“This is a significant advancement in the field of advanced prosthetic medicine,” said Lorenzo Andreani, MD. “The surgery was successful thanks to a careful patient selection process based on strict criteria. One of the most complex challenges was identifying the residual muscles in the amputation area, which were precisely selected using preoperative MRI imaging and electromyography. However, the actual condition of the tissue, due to scarring and fibrosis, required intraoperative adaptation.”
For each magnet, the team of surgeons and doctors located and isolated the muscle, positioned the magnet, and checked that the magnetic field was oriented in the same way.
“To make the connection between the residual arm where the magnets were implanted and the robotic hand easier, we made a carbon fiber prosthetic socket containing the electronic system capable of localizing the movement of the magnets,” Cipriani said.
The results of the experiment exceeded expectations, the researchers said. Daniel was able to control the movements of his fingers, he picked up and moved objects of different shapes, and performed actions such as opening a jar, using a screwdriver, cutting with a knife, and closing a zipper. He was able to control the force when he had to grasp fragile objects.
“This system allowed me to recover lost sensations and emotions. It feels like I’m moving my own hand,” Daniel said.
Editor’s note: This story was adapted from materials provided by Scuola Superiore Sant’Anna.
To watch a video of the process in English, visit the website.
The results, “Restoration of grasping in an upper limb amputee using the MyoKinetic prosthesis with implanted magnets,” were presented in Science Robotics.
