Figure 1.

Schematic overview of fabrication of scaffold-free zonally-stratified articular cartilage: human ADSCs were expanded and differentiated under chondrogenic induction followed by centrifuging them to obtain dense pellet. Cells were then microinjected into alginate capsules to facilitate cell aggregation followed by de-crosslinking of alginate capsules to obtain TSs. Zonally-stratified cartilage was comprised of the vertically aligned bottom zone, which was fabricated using an aspiration-assisted bioprinting (AAB) technique with the assistance of a pin array and the superficial zone, which was bioprinted using an extrusion-based bioprinting technique. After tissue fusion, the superficial zone was transferred onto the bottom zone and assembled via tissue fusion.