A One‐Stone‐Two‐Birds Strategy for Osteochondral Regeneration Based on a 3D Printable Biomimetic Scaffold with Kartogenin Biochemical Stimuli Gradient

Osteochondral defect (OCD) regeneration remains challenging because of the hierarchy of the native tissue including both the articular cartilage and the subchondral bone. Constructing an osteochondral scaffold with biomimetic composition, structure, and biological functionality is the key to achieve its high‐quality repair. In the present study, an injectable and 3D printable bilayered osteochondral hydrogel based on compositional gradient of methacrylated sodium alginate, gelatin methacryloyl, and β‐tricalcium phosphate (β‐TCP), as well as the biochemical gradient of kartogenin (KGN) in the two well‐integrated zones of chondral layer hydrogel (CLH) and osseous layer hydrogel (OLH) is developed. In vitro and subcutaneous in vivo evaluations reveal that apart from the chondrogenesis of the embedded bone mesenchymal stem cells induced by CLH with a high concentration of KGN, a low concentration of KGN with β‐TCP in the OLH synergistically achieves superior osteogenic differentiation by endochondral ossification, instead of the intramembranous ossification using OLH with only β‐TCP. The biomimetic construct leveraging KGN as the only biochemical inducer can facilitate cartilage and subchondral bone restoration in the in vivo osteochondral defect. This one‐stone‐two‐birds strategy opens up a new facile approach for OCD regeneration by exploiting the biological functions of the bioactive drug molecule KGN. An injectable biomimetic scaffold is constructed for osteochondral defect regeneration. Kartogenin (KGN) is used as the only bioactive drug molecule to achieve the "one‐stone‐two‐birds" strategy. A high concentration of KGN in the chondral layer hydrogel can induce the chondrogenesis of bone marrow mesenchymal stem cells (BMSCs), while a low concentration of KGN with β‐tricalcium phosphate (β‐TCP) can realize superior osteogenic differentiation of BMSCs by endochondral ossification.