The Advanced Planning and 3D Manufacturing Unit (UPAM3D) at Gregorio Marañón University General Hospital, part of the Community of Madrid, has reportedly designed, manufactured and implanted the world’s first personalized metamaterial bone prosthesis. Almost a year after the surgery, the patient, a 38-year-old man treated for a high-grade bone sarcoma in the tibia, has shown no infection or related complications, has retained knee alignment and mobility, and can now walk, in many cases without crutches.
The prosthesis was manufactured from a titanium alloy using 3D printing inside the hospital itself, a solution adopted because no implant on the market was capable of saving the patient’s leg without compromising knee mobility. The device was fitted by the hospital’s oncological surgeons and developed through a partnership between the Gregorio Marañón Health Research Institute and the Polytechnic University of Madrid.
A structure that mimics bone
The device draws on aerospace-derived technology: metamaterial structures made up of millimeter-scale rods that recreate both the shape and function of bone. Rather than replacing the original bone, the prosthesis imitates it, absorbing mechanical load and preventing the surrounding bone tissue from weakening through disuse. The piece weighs just 300 grams yet withstands more than 500 kilograms of weight.
The medical team introduced a further innovation in this case: the prosthesis was filled with cancellous bone from the Gregorio Marañón Hospital’s own Bone and Osteotendinous Tissue Bank. The graft became interwoven within the metal structure, aiding bone integration and implant fixation. The operation proceeded without complications, and subsequent imaging tests confirmed the favorable adaptation of these elements.
Why a conventional implant wouldn’t work
The patient had suffered an infection and a severe reduction in bone density in the tibia, meaning the bone could not support a conventional implant. Faced with this limitation, the hospital’s medical team considered a personalized device, one adapted not only to the patient’s anatomy, but to the specific function of the affected limb.
The design was based on the patient’s radiological images, from which the team built a digital twin of his healthy leg. Real-world loads placed on a tibia while walking, climbing stairs or stumbling were simulated on this model. Using that data, the team calculated point by point how the piece’s internal lattice needed to be configured so that weight was transmitted precisely to the areas the bone could bear. This process allowed the fixation screws to be oriented toward the areas of best bone quality, and the surgery to be planned with millimeter precision.
Spain’s push into hospital-based 3D manufacturing
The Gregorio Marañón implant comes as Spanish public hospitals are increasingly treating 3D printing as a certified manufacturing activity rather than an experimental support tool.
At Hospital Universitario 12 de Octubre, also in Madrid, the Advanced Technologies in Design and 3D Printing Unit (UTADI 3D) recently became the first public unit in Spain to hold dual design and manufacturing certification for custom medical devices under the UNE-EN ISO 13485:2018 standard, expanding its remit beyond radiotherapy molds into a wider range of patient-specific devices. The unit now supports 33 services across the hospital and belongs to a national reference network coordinated by the Instituto de Salud Carlos III, a sign that formal accreditation, along with the underlying technology, is what is allowing Spanish hospitals to move from printing prototypes to manufacturing devices used directly in patient care.
Custom implants in orthopedic oncology
In orthopedic oncology, standard implants have long forced compromises on mobility, fit and durability. Surgical teams are increasingly using CT and MRI scans from the outset to design devices matched to each patient’s bone geometry, load profile and the exact defect left after tumor removal.
This approach has already shown results elsewhere. Researchers at Guangxi Medical University Hospital in China used custom titanium prostheses with mesh patches to treat five patients with distal radius giant cell tumors between 2018 and 2021, improving ligament attachment, joint stability and early wrist mobility by precisely matching each patient’s anatomy.
In India, Manipal Hospitals used CT scans to design a personalized 3D printed titanium chest bone for a patient whose sternum and ribcage had been destroyed by a large tumor, replacing the entire structure after its removal.
Gregorio Marañón’s metamaterial prosthesis goes a step further, replicating not just the shape of the missing bone but its mechanical behavior under load.
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Featured image shows Gregorio Marañón Hospital Implants Personalized Metamaterial Bone Prosthesis. Photo via Gregorio Marañón University General Hospital.