Abstract
Hierarchical structure has exhibited an important influence in the fields of supercapacitors, catalytic applications, and tissue engineering. The hot dog, a popular food, is composed of bread and sausage with special structures. In this study, inspired by the structure of a hot dog, the strategy of combining direct ink writing 3D printing with bidirectional freezing is devised to prepare hot dog-like scaffolds with hierarchical structure. The scaffolds are composed of hollow bioceramic tubes (mimicking the "bread" in hot dogs, pore size: ≈1 mm) embedded by bioceramic rods (mimicking the "sausage" in hot dogs, diameter: ≈500 µm) and the sausage-like bioceramic rods possess uniformly aligned lamellar micropores (lamellar pore size: ≈30 µm). By mimicking the functions of hierarchical structure of bone tissues for transporting and storing nutrients, the prepared hot dog-like scaffolds show excellent properties for loading and releasing drugs and proteins as well as for improving the delivery and differentiation of tissue cells. The in vivo study further demonstrates that both the hierarchical structure itself and the controlled drug delivery in hot dog-like scaffolds significantly contribute to the improved bone-forming bioactivity. This study suggests that the prepared hot dog-like scaffolds are a promising biomaterial for drug delivery, tissue engineering, and regenerative medicine.