Sergio Sánchez and Javier Blanco, both 26 years old and from Madrid, are always friends, “since school,” says the second. In 2020, they were studying a master’s degree in 3D printing and advanced manufacturing together when they decided that their Master’s Thesis (TFM) could be used to help their friend Sara Martín. The 24-year-old was born without her left forearm and hand and they created a prosthesis for both limbs. “We wanted to mix engineering with medicine. We proposed it to Sara and she immediately said that she was ”, they say excitedly.
Three years later they are already on the second version: “I started using the previous model, but they immediately told me that they could improve it,” says the young woman from Madrid. The first prosthesis they developed was mechanical. It worked through some cables that connected Martín’s elbow with the artificial hand, so that when he bent the elbow, the hand closed. The second version is myoelectric. In other words, it has electronics and has two electrodes connected to the flexor and extensor muscles of the hand, on the arm, to perform the opening and closing movements of the hand.
“We take a muscle that, due to the lack of a limb, has no function and we give it to it thanks to the sensors,” explains Blanco. The sensors transmit via bluetooth the electrical signals emitted by the muscles to a mobile phone, which converts them into specific orders. In this way, when Martin squeezes one of the muscles, the hand opens or closes.
The woman from Madrid had used other aesthetic prostheses before, without functionality, but she did not like them. “They were very heavy, they were very artificial and in the end I got used to not wearing them,” says the young woman. She had also tried other myoelectric models, but she had the same problem with her weight, they were too big for her and “they cost an awful lot”. Martín complains that, although there is aid, not all models are eligible for it and funding is scarce.
One of the advantages of 3D printing technology in cases like this is that it lowers costs. Without counting the hours of work, Blanco and Sánchez calculated that the cost of manufacturing the first prosthesis is around 60 or 80 euros. In the case of the second, as it is a more complex system, the amount would amount to around 200 euros, although this figure is not specified because the myoelectric prototype is not finished and they are still making adjustments.
Being a TFM project, the vast majority of the costs have been assumed by the center where they were studying, the EDDM engineering school in Madrid, so they have hardly had to make any economic contribution. They assume that, in the event that their prototype becomes a real product, its final sale price would be 1,000 euros for the first model and 1,500 euros for the second.
Before starting the project, they did a market study to find out what investment a prosthesis of these types could entail. They would cost around 2,300 and 4,000 euros respectively, a calculation they made with the prices of the catalog of orthopedic services of the Ministry of Health. However, “the prices marked there are well below the real prices,” acknowledges Blanco.
Another advantage of this technology is that it allows a fairly high degree of customization, the three young people point out. “The important thing was that it was the most useful and comfortable for Sara,” explains Sánchez convinced. To make the prostheses, they scanned Martín’s right forearm and hand to take the measurements and make them as symmetrical as possible. They also talked with the young woman about what she expected from her and what they could improve on from previous experiences she had had. The final result is made up of 28 pieces on the fingers, three on the hand, two on the forearm and two hooks.
The first afternoon that Sara tried the prosthesis, she controlled it wonderfully.
Sergio Sánchez, creator of the prosthesis
The two students point out that it took the young woman very little to learn how to use her first prosthesis. “We expected her to take several days to get used to, but the first afternoon she tried it she handled it great,” Blanco says proudly. Martín, for his part, expresses the difficulty that this entails: “You have to learn to control muscles that you don’t use regularly.”
The young woman tells of the improvement it has brought to her day-to-day life, even though “she doesn’t need it to live”. Unlike the previous ones that she had used, she says that she now has a prosthesis that helps her and is really useful. As it is a project outside of her work, they cannot spend as much time on it as they would like. Martín does not have it in her possession yet because Sánchez and Blanco have not finished all the work and are still making some adjustments.
Alfonso Denia, founder and CEO of EDDM explains that this is the first time that such a project has been developed in the center. “Everything that has to do with biomedicine is going perfectly because, in addition, it is an area that is seen in the master’s degree,” he says and, like his students, highlights the economic nature: “A 3D printer of thousands is not necessary of euros to be able to do something like that”.
The authors of the work were clear that they wanted to “do something that would really help someone, who would really benefit from it.” After finishing the master’s degree, Sánchez no longer has anything to do with orthopedics, he is dedicated to the aeronautics sector, but Blanco has continued training in that field: “I would like to continue combining technology and science to improve life of people”.
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