High-Strength Hydroxyapatite Scaffolds with Minimal Surface Macrostructures for Load-Bearing Bone Regeneration

Triply periodic minimum surfaces (TPMS), which outperform other structures in terms of bulk moduli and relative density, have been widely used to dramatically improve the mechanical strength of natural echinoderm skeletons and engineered scaffolds. Herein, TPMS-structure-based 3D-printed hydroxyapatite (HAp) scaffolds to highly improve their limited mechanical strength and evaluate the underlying mechanism in terms of mechanical match and biological bone repair process as a bone regeneration scaffold are constructed. The results show that TPMS-structure-based HAp scaffolds have a greater compressive strength range that is sufficient to meet the strength requirements for human cortical and trabecular bone, and outperform traditional HAp scaffolds with Cross-hatch structures in terms of compressive strength, cell density, and osteogenic differentiation. The reduction of stress concentration and open-cell permeable structure of Split-P scaffolds can benefit the generation and ingrowth of new bone after the in vivo implantation in the rabbit femur bone. Furthermore, RNA-seq and immunochemistry staining results of in vivo samples unravel the bone repair mechanism in a time sequence. The optimized scaffolds with TPMS macrostructures and an in-depth understanding of repair mechanisms will contribute to the development of bone regeneration materials that perform on par with load-bearing bone.