Bioinspired fractal design and additive manufacturing of radial gradient porous bone scaffold: Towards tunable porosity, mechanical properties and permeability

The single and homogeneous pore structure of bone scaffold often struggle to simultaneously meet the dual requirements of natural bone for porosity and mechanical properties, thereby limiting the efficacy of bone regeneration. Herein, inspired by the honeycomb and branching structures found in nature, the poly (l-lactide) scaffold with radial gradient porous structure was designed using biomimetic and fractal design methodologies, and then fabricated by fused deposition modeling technology. By adjusting the wall thickness of honeycomb structure and iteration number of fractal structure, the characteristic of natural bone porosity, which gradually decreased from the center to the periphery, was simulated. Mechanical testing results indicated that the compressive properties of the scaffold improved with increasing iteration order, which was due to the increased contact area between the fractal-structure layer and the honeycomb-structure layer. Permeability experiments and simulation analyses demonstrated that from the first-order to fourth-order scaffolds, both porosity and overall permeability exhibited gradual decreasing trend, while the overall permeability of all scaffolds remained higher than that of natural bone. Considering both compression and permeability, the third-order scaffold performed best. Overall, this work aims to present a strategy for designing scaffold with tailored pore distributions, mechanical properties and permeability to meet diverse requirements.