Strength study of anatomically-similar spongy structures additively manufactured from polymeric materials

The subject of the article is to investigate the potential to adjust the stiffness of 3D printed plastic implants to match bone stiffness by analyzing design parameters and mechanical properties, considering the spongy structure of the bone. The study consisted of theoretical and practical parts, including original research. In the theoretical part, the definition of implants, the materials used for their production, and the requirements they must meet were discussed, as well as 3D printing methods, with particular emphasis on the FFF method. The static compression test was also described. In the practical part, original research was conducted to verify the possibilities of adjusting the stiffness of the implants. Two 3D models of the L2 lumbar vertebra with different vertebral body thicknesses and internal lattice structures were developed based on literature dimensions. Thirty models with three different lattice densities and two wall thicknesses were printed and subjected to a static compression test. The results showed that an increase in lattice density increased the compression strength of the samples. Samples with thin walls exhibited lower compression strength compared to those with thick walls, regardless of the spongy lattice density. In each group of samples, the results were consistent, indicating good repeatability of the prepared samples. The findings suggest that appropriately selecting the lattice density and wall thickness can significantly improve the mechanical strength of bone implants, meeting the compression strength criteria for the spongy tissue of lumbar vertebrae.