Advances in 3D-printed hierarchical scaffolds for load-bearing bone reconstruction: bridging the gap between traditional approaches and next-generation tissue engineering approaches

Critical-sized long bone defects remain a major clinical challenge because of their limited self-healing capacity and the high mechanical demands of load-bearing environments. Tissue engineering offers promising alternative approaches over conventional load bearing bone tissue reconstruction strategies. This review outlines the limitations of traditional bone repair methods and recent progress in 3D printing-based reconstruction strategies. Further, key design principles for hierarchical scaffold architectures were examined, focusing on biomimetic pore size and porosity gradients, multiscale nano–micro–macro organization, mechanical optimization for effective load transfer, and topologically interlocking or compartmentalized structures. The materials section comprises established printable polymers and ceramics, as well as composite and emerging smart materials, such as stimuli-responsive and self-healing systems, that aim to integrate structural function with controlled biological signaling. Finally, we compare conventional, composite, and emerging smart biomaterials, discussing current preclinical evidence, remaining challenges, and future directions toward clinically translatable, mechanically robust bone regeneration solutions.