Orthopedic implants with metal 3D printing

First used in medicine and now largely in dentistry and tool making, the next step for 3D printing (3DP) will be its use in more demanding orthopedic implant applications, where surgeons currently have to rely on standard-sized machined implants without the possibility of customization.

For example, personalized pore structures enabled by 3DP allow the mechanical properties of implants to be optimized to resemble bone. Biomechanical stimulation enables bone tissue growth in the implant, promoting osseointegration, mitigating stress damage at the bone-implant interface, and extending the life of the implant.

“The development of custom-made implants allows for better coupling and adjustment between bone and implant using osseointegration,” says researcher Miguel Araya Calvo from the Costa Rican Institute of Technology. “Furthermore, the digitized process from CT imaging to the fabrication of a customized implant will enable implementation of custom interventions such as surgical planning and the development of customized guides that reduce the time, cost, and risk of the surgical procedure.”

As a digital fabrication technique, 3DP has been integrated with existing CT scanning systems to allow imaging to create digital models. This has led to a faster manufacturing process and improved product quality.

“3D printing enables the realization of complex structures that cannot be achieved by other manufacturing methods,” says Kari Mäntyjärvi, development manager of the Future Manufacturing Technologies (FMT) research group at the Kerttu Saalasti Institute, University of Oulu. “This allows, for example, the design of lightweight and durable structures, with optimization focused on very small details. So you go from the macro to the micro level. This can be used in different application areas, such as medicine.”

3DP offers fast manufacturing of custom implants, using a similar process already commercialized by dentistry. 3DP’s manufacturing accuracy and near-free geometry control provide a completely new starting point for developing implant structures. By exploiting the specificities of the manufacturing process, the shortcomings of traditional implants, in terms of mechanical properties and biocompatibility, can be addressed.

Research by the FMT group in collaboration with the Costa Rican Institute of Technology has shown by 3DP purpose-designed pore structures instead of solid structures, the flexibility of metal structures can be optimized to suit different bone types. In addition, porosity can be controlled in a gradual way so the implant surface can be made partially solid for durability but porous for tissue adhesion and structural flexibility.

The new type of implant developed takes advantage of both features so it can be fixed to the bone as a constrained connection without screws, as the bone tissue grows into the implant from the porous areas. The highly porous inner structure of the implant provides an excellent platform for the growth of different cells such as blood vessels and nerve tissue.

Durability tests of metallic lattice structures have been carried out at the University of Ouluon a laboratory scale according to medical standards with promising results. Pre-clinical trials will start in February in Costa Rica, when researchers from the FMT team travel with 3D-printed metal samples for a two-week research visit. The metal samples will be mounted on animal bones for mechanical laboratory testing and biocompatibility experiments.

University of Oulu
https://www.oulu.fi/en