Two years after losing his left hand in an accident, Daniel can pick up an egg without breaking it, use a screwdriver or cut bread with a knife. And he does so using the first bionic hand connected to his body magnetically, without cables or electrodes. A system that allows fine finger movements thanks to small magnets implanted in the muscles that remained in the severed area.
The details of this progress, framed within the project WASH funded by the European Research Council, are published this Wednesday in the magazine Science RoboticsThe study describes the strategy that has allowed this 34-year-old Italian to use the bionic hand to tie his shoelaces and take pills out of a blister pack. “This system allowed me to recover lost sensations and emotions: I feel as if I were moving my own hand,” says Daniel.
The prostheses commonly fitted 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 movement of the prosthesis. This technology relies heavily on brain signals to control the prostheses, which lack the ability to reproduce the dexterous movements of the natural human hand, the authors say, and are often rejected by patients after a time.
Magnets that direct the movement
The new strategy, developed by a research team from the Biorobotics Institute of the Sant’Anna High School from Pisa and coordinated by Christian Ciprianiis 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, a few millimetres in size, in the residual muscles of the amputated arm and installing a system in the prosthesis that translates these changes in the position of the magnetic fields into movements to open and close the fingers with precision.
“There are 20 muscles in the forearm, and many of them control hand movements. Many people who have lost a hand still feel it as if it were still there, and the residual muscles move in response to commands from the brain,” explains Cipriani. “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 leader 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 checked that the magnetic field was oriented in the same way. A transcutaneous magnetic locator located in the prosthesis detects the displacements of the magnet 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 fruit 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.” In his opinion, these implants will in the future make it possible to perform tasks that require great skill, such as playing the piano. “We have become aware that we can do a lot to improve his life and that of many other people,” he adds. Marta Gherardinifirst 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 we can do a lot to improve your life and that of many other people.
Marta Gherardini
— First author of the study
The authors suggest that future prosthetics could support more severe amputations and reduce user abandonment 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 fast adaptation
Anthony Oliverhead of Neurology at the National Hospital for Paraplegics (Toledo), believes that the authors have made an approach similar to that of the myoelectric prosthesis, but with the advantage of using the muscle by coupling small magnets to it. “When the person thinks about 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 that it does allow for faster learning, in just six weeks.” In his opinion, 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 which cause them to stop using them.
Jaime Ibanez Peredaa researcher at the University of Zaragoza and an expert in biomedical signal interpretation, considers that this is a very intelligent approach. “If we put magnets in the muscles, then all the technological complexity is placed 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 one subject, but also that the prosthesis is very dependent on position, and when the subject moved the elbow, precision was lost, although they propose adopting improvements to avoid this.
The user may feel it in a slightly more natural way, 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 biomedical signal interpretation
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 tissue will grow that worsens the signal and requires them to be replaced from time to time, as happens with electrodes.
“It may also feel a little more natural to the user, because the force applied by moving the hand is derived from how much the muscle is deformed rather than electrical activity, which may be more intuitive,” he adds. However, it also creates more uncertainty, since the amount of movement generated and “translatable” – especially in severely damaged patients – is limited, whereas in reading the electrical signal the range is wider and weaker signals can be detected.
A path to tactile sensations
“The article presents an interesting, innovative and potentially disruptive paradigm shift,” says the biomedical engineer. Francesca Lunardini According to elDiario.es, this innovative approach offers several advantages compared to traditional electromyographic sensors: the interface is small and, most importantly, it does not require wireless power or cables.
“But the potentially disruptive feature of the proposed technology is its potential bi-directional communication function: on the one hand, it serves as a sensor to measure and detect the user’s intention, while on the other, it can be used as an actuator to provoke natural vibrotactile and kinesthetic sensations,” Lunardini points out. In other words, the patient can feel the limb. “This could be achieved, for example, by activating remote vibrations in the magnets to activate the proprioceptive muscle receptors.”
The system can be leveraged to elicit natural vibrotactile and kinesthetic sensations and establish bidirectional communication with the prosthesis.
Francesca Lunardini
— Biomedical Engineer
“The current paper, with a six-week study in a transradial amputee, not only demonstrates the clinical feasibility of the approach to bionic hand control, but also reports very promising results,” she concludes. “Although some conceptual and technical limitations need to be addressed, the results pave the way towards an innovative human-machine interaction solution, capable of providing the user with direct two-way communication with the prosthesis, just like the natural hand.”
Source: www.eldiario.es
