3D-printed surgical guides to refine implantation research

Medical bone implants, such as screws or artificial joints, play a major role in orthopedic surgery and dental medicine. Osseointegration, which is the formation of new bone at the surface of the implant as well as the functional connection between bone and implant, is decisive for stable anchoring of the implant and its durability. To study the process of osseointegration under experimental conditions such as osteoporosis, an animal model in the rat is used worldwide as the gold standard. In this model, screws with a typical size of 1- 2 mm are implanted into the tibia bone of rats prior to histological assessment of osseointegration. The exact positioning of the screws is crucial for successful osseointegration; however, its flawless realization is a major obstacle that frequently results in failed experiments and an exaggerated number of used animals. The PRECISE project aims to solve this scientific and ethical problem by the use of 3D- printed surgical guides that exactly fit the shape of the rat tibia bone and allow precise positioning of the screws. To this end, tibia bones of three standard rat phenotypes will be scanned prior to the virtual design of accurately fitting surgical guides. These guides will then be fabricated in plastic and metal using three different 3D printing technologies. The applicability of the guides is then evaluated independently by two surgeons in rat cadavers. The blueprints of the best performing guides will be provided to the worldwide community via databases. In a next step, a special imaging device (in vivo CT) will be implemented into the workflow to allow 3D reconstruction of the tibia bones from living animals. Thereby, it will be possible to design individual surgical guides for practically every rat phenotype (different age, size, sex, disease context, etc.). Both approaches, the general and the customized design, will be compared in their practicability and implementation. Finally, the PRECISE project will for the first time systematically evaluate the impact of implant positioning (i.e., distance from the growth plate) on osseointegration. In this context, rats with compromised bone quality as well as the in vivo CT technology will be used to assess the process of osseointegration in vivo over time. In summary, the PRECISE project is expected to contribute to the standardization of the rat tibia osseointegration model, to refine the method and reduce the number of animals used in future scientific studies.