3D-printed biomimetic scaffolds with precisely controlled and tunable structures guide cell migration and promote regeneration of osteochondral defect.

Untreated osteochondral defects will develop into osteoarthritis, affecting patients' quality of life. Since articular cartilage and subchondral bone exhibit distinct biological characteristics, repairing osteochondral defects remains a major challenge. Previous studies have tried to fabricate multilayer scaffolds with traditional methods or 3D printing technology. However, the efficacy is unsatisfactory because of poor control over internal structures or a lack of integrity between adjacent layers, severely compromising repair outcomes. Therefore, there is a need for a biomimetic scaffold that can simultaneously boost osteochondral defect regeneration in both structure and function. Herein, an integrated bilayer scaffold with precisely controlled structures is successfully 3D-printed in one step via digital light processing (DLP) technology. The upper layer has both 'lotus- and radial-' distribution pores, and the bottom layer has 'lotus-' pores to guide and facilitate the migration of chondrocytes and bone marrow mesenchymal stem cells, respectively, to the defect area. Tuning pore sizes could modulate the mechanical properties of scaffolds easily. Results show that 3D-printed porous structures allow significantly more cells to infiltrate into the area of 'lotus- and radial-' distribution pores during cell migration assay, subcutaneous implantation, andtransplantation, which are essential for osteochondral repair. Transplantation of this 3D-printed bilayer scaffold exhibits a promising osteochondral repair effect in rabbits. Incorporation of Kartogenin into the upper layer of scaffolds further induces better cartilage formation. Combining small molecules/drugs and precisely size-controlled and layer-specific porous structure via DLP technology, this 3D-printed bilayer scaffold is expected to be a potential strategy for osteochondral regeneration.