Experimental tests on robotic prosthesis: clothespin (Credit: © 2024 Scuola Superiore Sant’Anna)
‘This system allowed me to recover lost sensations and emotions: it feels like I’m moving my own hand.’
PISA, Italy — In a groundbreaking development, researchers have created a new way for amputees to control prosthetic hands using tiny magnets implanted in their muscles. This innovative approach, called the myokinetic interface, could revolutionize how artificial limbs are controlled, offering more intuitive and natural movement for users.
The study, conducted by a team of Italian scientists and published in Science Robotics, demonstrates how this magnetic method can allow an amputee to perform complex tasks like tying shoelaces or manipulating fragile objects – abilities that have long been challenging for people using standard artificial limbs.
Imagine losing your hand in an accident. Suddenly, simple tasks like buttoning a shirt or holding a cup become monumental challenges. Current prosthetic hands, while helpful, often fall short of providing the dexterity and fine control needed for many everyday activities. They typically rely on electrical signals from remaining muscles, which can be difficult to control precisely.
Daniel, the first patient to test the myokinetic interface, lost his left hand in 2022.
“I suddenly found myself without a hand: one moment I had it and the next moment it was gone,” Daniel recalls.
This new system uses small, powerful magnets – each about the size of a grain of rice – surgically implanted into an amputee’s residual arm muscles. As the person thinks about moving their phantom hand, these muscles contract, causing the magnets to shift slightly. Special sensors in the prosthetic socket detect these tiny movements, translating them into commands for the robotic hand.
“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,” explains Christian Cipriani, a professor at the BioRobotics Institute of the Scuola Superiore Sant’Anna, in a media release.
The researchers tested their system with Daniel, who had lost his left forearm in an accident. Six magnets were implanted in three of his residual arm muscles. After just six weeks of training, he was able to perform a variety of tasks with the prosthetic hand, including picking up an egg without breaking it and extracting pills from a blister pack.
Perhaps most impressively, Daniel could tie his shoelaces using the prosthetic hand – a task that requires intricate coordination and fine motor control. This level of dexterity is rarely seen with traditional prosthetic systems.
“This system allowed me to recover lost sensations and emotions: it feels like I’m moving my own hand,” Daniel says.
“This result rewards a decades-long research path. We have finally developed a functional prosthesis that meets the needs of a person who has lost a hand,” adds Prof. Cipriani.
The myokinetic interface isn’t just about improved control. Since the magnets are completely passive, requiring no batteries or wires, they could potentially last a lifetime once implanted. This longevity could significantly reduce the need for invasive follow-up surgeries that are sometimes required with other implanted prosthetic control systems.
While the results are promising, the technology is still in its early stages. The researchers acknowledge that further refinement is necessary before it can be widely adopted. However, they believe that with continued development, the myokinetic interface could offer amputees a level of prosthetic control closer to that of a natural hand than ever before.
As this technology evolves, it could open up new possibilities for amputees, allowing them to regain abilities they thought were lost forever. From playing a musical instrument to performing delicate tasks in the workplace, the myokinetic interface might just be the key to unlocking a new era of prosthetic functionality.
Paper Summary
Methodology
The researchers implanted six small magnets into three arm muscles of a man who had lost his left forearm. They then created a special prosthetic socket filled with sensors that could detect the movements of these magnets. When the user thought about moving his hand, his muscles would contract, moving the magnets. The sensors would pick up these movements and translate them into commands for the prosthetic hand. The team tested two ways of interpreting these signals: a direct control method where specific muscle movements corresponded to specific hand actions, and a pattern recognition approach that used machine learning to interpret more complex patterns of muscle activity.
Key Results
After six weeks of training, the participant was able to use the prosthetic hand to complete several standardized tests used to evaluate hand function. His performance was similar to what he achieved with a traditional myoelectric prosthesis (controlled by electrical signals from muscles). He was also able to perform complex real-world tasks like tying shoelaces and handling fragile objects. The system using pattern recognition to interpret muscle movements showed particularly promising results in terms of precise control.
Study Limitations
The study only involved one participant over a short period of time, so more research is needed to confirm the long-term effectiveness and safety of the approach. The implanted magnets didn’t move as much as hoped within the muscles, which limited the precision of control. The prosthetic socket sometimes interfered with the magnetic signals, particularly when the elbow was bent. The system also required recalibration each time the prosthesis was put on.
Discussion & Takeaways
This study demonstrates that the myokinetic interface is a viable approach for controlling advanced prosthetic hands. It offers the potential for more intuitive control compared to traditional methods. The researchers believe that with further refinements, such as improved surgical techniques for implanting the magnets and better socket designs, the system could offer even more precise control. They also suggest that this technology could be combined with other advanced prosthetic techniques to further improve functionality.
Funding & Disclosures
The study was primarily funded by the European Research Council and the Italian Ministry of Research. Two of the study authors hold shares in Prensilia S.r.l., a company that develops advanced robotic hands and prostheses.
