3D-bioprinted anisotropic bicellular living hydrogels boost osteochondral regeneration via reconstruction of cartilage–bone interface

Reconstruction of osteochondral (OC) defects represents an immense challenge due to the need for synchronous regeneration of special stratified tissues. The revolutionary innovation of bioprinting provides a robust method for precise fabrication of tissue-engineered OCs with hierarchical structure; however, their spatial living cues for simultaneous fulfilment of osteogenesis and chondrogenesis to reconstruct the cartilage-bone interface of OC are underappreciated. Here, inspired by natural OC bilayer features, anisotropic bicellular living hydrogels (ABLHs) simultaneously embedding articular cartilage progenitor cells (ACPCs) and bone mesenchymal stem cells (BMSCs) in stratified layers were precisely fabricated via two-channel extrusion bioprinting. The optimum formulation of the 7% GelMA/3% AlgMA hydrogel bioink was demonstrated, with excellent printability at room temperature and maintained high cell viability. Moreover, the chondrogenic ability of ACPCs and the osteogenic ability of BMSCs were demonstrated in vitro, confirming the inherent differential spatial regulation of ABLHs. In addition, ABLHs exhibited satisfactory synchronous regeneration of cartilage and subchondral bone in vivo. Compared with homogeneous hydrogels, the neo-cartilage and neo-bone in ABLHs were augmented by 23.5% and 20.8%, respectively, and more important, a more harmonious cartilage-bone interface was achieved by ABLHs due to their well-tuned cartilage-bone-vessel crosstalk. We anticipate that such a strategy of tissue-mimetic ABLH by means of bioprinting is capable of spatiotemporal cell-driven regeneration, offering insights into the fabrication of anisotropic living materials for the reconstruction of complex organ defects.