Introduction: The repair of large segmental bone defects has always been a major challenge in clinical practice, and "stress shielding" caused by the mismatch in elastic modulus between the bone implant and the native bone is one of the key factors leading to implant failure.

Methods: Inspired by the branching structure of tree branches and trabecular bones, this study constructs a multi-level fractal scaffold geometric model with controllable fractal dimension, porosity, and pore size distribution. The influence of key structural parameters such as fractal iteration times, pore size, and trabecular diameter on the overall elastic modulus, compressive strength, and yield behavior of the scaffold was systematically studied using a combination of finite element calculations and mechanical experiments. Furthermore, scanning electron microscopy (SEM) was used to characterize the microstructure of the scaffolds fabricated by 3D printing.

Results: The porosity distribution of the 2-iteration and 3-iteration models is consistent with that of natural bone, featuring a radial gradient distribution with larger internal porosity and smaller external porosity. The elastic modulus of the 3-iteration model is 21% lower than that of the 2-iteration model, while its compressive strength is 17.3% higher than that of the 2-iteration model. The pore size of the fabricated scaffolds is consistent with that of the designed model, with a pore size error within 10%, indicating that the multi-level fractal scaffold designed in this study has good processability.

Conclusions: The 3-iteration fractal scaffold has higher strength and lower elastic modulus, which is similar to the mechanical properties of natural bone and can effectively alleviate stress shielding. The bionic scaffold based on fractal theory and the research on its structure-modulus matching proposed in this study can provide a new idea for alleviating the stress shielding of implants.