Two years after losing his left hand in an accident, Daniel can pick up an egg without breaking it, using a screwdriver or cutting bread with a knife. And this is thanks to the first bionic hand magnetically connected to your body, without cables or electrodes. A system that allows fine movements of the fingers thanks to small magnets implanted in the muscles remaining in the severed area.
Details of this breakthrough, framed within the framework of the MYTI project, financed by the European Research Council, are published this Wednesday in the journal Scientific robotics. The study describes the strategy that allowed the 34-year-old Italian to use his bionic hand to tie his shoelaces and take pills from blister packs. “This system has allowed me to regain lost sensations and emotions: I feel like I’m moving my own hand,” Daniel explains.
The prosthetics usually given to amputees are “myoelectric,” which work by using electrodes placed on the surface of the skin or inserted into nerves that pick up electrical currents that translate into the movement of the prosthesis. This technology relies heavily on brain signals to control the prostheses, which the authors say lack the ability to replicate the dexterous movements of the natural human hand, and are often rejected by patients after a while.
Magnets that direct the movement
The new strategy, developed by a research team from the Institute of Biorobotics of Sant’Anna High School from Pisa and coordinated by Christian Cipriani, is based on “myokinetic” control, that is, the decoding of motor intentions by translating the movement of the muscles and not the signal from the nerves. The strategy consists of implanting a series of small magnets of a few millimeters in the residual muscles of the amputated arm and installing in the prosthesis a system that translates these changes in the position of the magnetic fields into opening and closing movements of the amputated arm. fingers with precision.
“There are 20 muscles in the forearm and many of them control the movements of the hand. Many people who have lost a hand continue to feel as if it is still there and that the residual muscles move in response to commands from the brain,” Cipriani explains. “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.”
When the muscle contracts, the magnet moves and a special algorithm translates this change into a specific command for the robotic hand.
Christian Cipriani
— Researcher at the Scuola Superiore Sant’Anna in Pisa and head of the study
In April 2023, Daniel underwent surgery in which six magnets were implanted in his arm. In each of them, the team of surgeons and doctors located and isolated each muscle, placed the magnet, and verified that the magnetic field was oriented in the same way. A transcutaneous magnetic locator located on the prosthesis detects magnetic displacements caused by the subject’s voluntary muscle contractions, which the researchers combine with pattern recognition algorithms to estimate the user’s intention and move the robotic arm.
Towards more precise and durable prostheses
“This result is the result of decades of research,” Cipriani sums up. “We have finally developed a functional prosthesis that meets the needs of a person who has lost a hand.” According to him, these implants will allow in the future to perform tasks that require great skill, such as playing the piano. “We have realized that we can do a lot to improve their lives and those of many other people,” adds Marta Gherardini, first author of the study. “This is the greatest motivation that drives us to continue our work and to do it better and better.”
We have realized that there is a lot we can do to improve your life and the lives of many other people.
Marta Gherardini
— First author of the study
The authors suggest that future prosthetics could withstand more severe amputations and reduce user dropout rates. And, with some adaptations, the device could integrate and translate elbow flexion, upper arm contractions and wrist angle to open or close the bionic hand, something it cannot do at present.
A very rapid adaptation
Antonio Oliviero, head of the neurology department of the National Paraplegic Hospital (Toledo), believes that the authors have taken an approach similar to that of the myoelectric prosthesis, but with the advantage of using the muscle by attaching small magnets to it. “When the person thinks about the movement and the muscle deforms, the attraction of these magnets changes and there is a sensor that interprets it and transfers it to the robotic arm,” he explains. “This prosthesis is no less complex, but it seems to allow faster learning, in just six weeks.” According to him, it is an interesting and simple approach that will probably allow many patients to use it without having the problems that they sometimes have with traditional prostheses and why they stop using them.
Jaime Ibáñez Pereda, a researcher at the University of Zaragoza and an expert in the interpretation of biomedical signals, considers this to be a very intelligent approach. “If we put magnets in the muscles, then all the technological complexity is put in the robotic arm, the patient only needs the magnets,” he points out. The main limitation, he points out, is that they have only tested it on a single subject, but also that the prosthesis is very dependent on the position, and at the moment the subject moved the elbow, the precision was lost, although they propose to adopt improvements to avoid this.
The user may feel it a little more naturally, as it depends on the movement of the muscle and not the electrical signal.
Jaime Ibanez Pereda
— Researcher at the University of Zaragoza and expert in the interpretation of biomedical signals
In general, the expert points out, this type of prosthesis can have the advantage that the inserted magnets are more biocompatible and there is less chance that the body will reject them or that the tissues will grow, which worsens the signal and requires renewing them from time to time, as is the case with electrodes.
“It is also possible that the user feels it a little more naturally, because the force applied when moving the hand comes from the deformation of the muscle rather than from electrical activity, which can be more intuitive,” he adds. However, more uncertainty is also generated, because the amount of movement it generates and can be “translated” – especially in very damaged patients – is limited, while in reading the electrical signal the range is wider and detects weaker signals.
A route to tactile sensations
“The article presents an interesting, innovative and potentially disruptive paradigm shift,” biomedical engineer Francesca Lunarini tells elDiario.es. According to him, this innovative approach has several advantages over traditional electromyographic sensors: the interface has reduced dimensions and, above all, does not require wireless power or cables.
“But the potentially disruptive feature of the proposed technology is its possible bidirectional communication function: on the one hand, it serves as a sensor to measure and detect the user’s intention while, on the other hand, it can be used as an actuator to provoke natural reactions. vibrotactile and kinesthetic sensations,” Lunarini points out. In other words, let the patient palpate the limb. “This could be achieved, for example, by activating remote vibrations in the magnets to activate proprioceptive muscle receptors.”
The system can be used to elicit natural vibrotactile and kinesthetic sensations and establish two-way communication with the prosthesis.
Francesca Lunarini
— Biomedical engineer
“The present article, with a six-week study in a transradial amputee, not only demonstrates the clinical viability of the bionic hand control approach, but also reports very promising results,” concludes the specialist. “Although some conceptual and technical limitations need to be resolved, the results open the way to an innovative human-machine interaction solution, capable of providing the user with direct bidirectional communication with the prosthesis, like the natural hand.”
