Fractal Design Boosts Extrusion-Based 3D Printing of Bone-Mimicking Radial-Gradient Scaffolds

Although extrusion-based three-dimensional(EB-3D)printing technique has been widely used in the complex fabrication of bone tissue-engineered scaffolds,a natural bone-like radial-gradient scaffold by this processing method is of huge challenge and still unmet.Inspired by a typical fractal structure of Koch snowflake,for the first time,a fractal-like porous scaffold with a controllable hierarchical gradient in the radial direction is presented via fractal design and then implemented by EB-3D printing.This radial-gradient structure successfully mimics the radially gradual decrease in porosity of natural bone from cancellous bone to cortical bone.First,we create a design-to-fabrication workflow with embedding the graded data on basis of fractal design into digital processing to instruct the extrusion process of fractal-like scaffolds.Further,by a combination of suitable extruded inks,a series of bone-mimicking scaffolds with a 3-iteration fractal-like structure are fabricated to demonstrate their superiority,including radial porosity,mechanical property,and permeability.This study showcases a robust strategy to overcome the limitations of conventional EB-3D printers for the design and fabrication of functionally graded scaffolds,showing great potential in bone tissue engineering.