Hierarchical 3D-printed scaffolds for osteochondral regeneration: From Bio-mimetic design to functional integration

Osteochondral (OC) defects, characterized by the structural and functional disruption of articular cartilage and subchondral bone, present significant clinical challenges due to their limited intrinsic regenerate capacity. Scaffold-based tissue engineering has paved a way for OC defect treatment yet remains challenge to restore the complex structure and composition of native OC tissue. Recent advances in 3D printing enable the fabrication of layered anisotropic scaffolds that aim to biomimetically recapitulate the native tissue's zonal properties through precise hierarchical design. High-resolution fabrication techniques facilitate the construction of delicate microarchitectures, while advanced bioprinting methods allow for the incorporation of bioactive factors and cells into the scaffold. Emphasis is placed on four scaffold design paradigms in this review: composite gradients, microarchitectural patterning, biochemical gradients, and cellular heterogeneity. Moreover, key properties of multilayered scaffolds are discussed, including mechanical performance, interfacial strength, and degradation behavior. In addition, several obstacles associated with the in vivo application of scaffolds are discussed, providing insights for future clinical transformation of OC defects treatment.