Abstract: The custom-tailored medicine requires a developmental strategy that integrates excellent osteogenesis with mechanical stability to enhance the reconstruction of the critical-size bone defect (CSBD) and the healing process in weight-bearing bone. We prepared three-dimensional (3D) printed biphasic calcium phosphate (BCP) scaffolds composited with nano-graphene oxide (GO). The biological effects of the GO/BCP composite scaffolds could induce the differentiation of rat bone marrow stem cells (BMSCs) and the migration of human umbilical vein endothelial cells (HUVECs) for bone repair. The proper ratio of GO in the composite scaffold regulated the composites' surface roughness and hydrophilicity to a suitable range for the adhesion and proliferation of BMSCs and HUVECs. Besides, the GO/BCP composite scaffold increased osteogenesis and angiogenesis by activating BMP-2, RUNX-2, Smad1/4, and VEGF. The customized intramedullary nail combined with GO/BCP scaffold was applied to repair CSBD (2.0 cm in length) in a beagle femur model. This fixation strategy was confirmed by finite element analysis. In vivo, the results indicated that the custom-made internal fixation provided sufficient stability in the early stage, ensuring bone healing in a considerable mechanical environment. At 9 months postoperatively, longitudinal bony union and blood vessels in osteon were observed in the CSBD area with partial degradation in the 0.3% GO/BCP group. In the three-point bending test, the ultimate load of 0.3% GO/BCP group reached over 50% of the normal femur at 9 months after repair. These results showed a promising application of osteogenic GO/BCP scaffold and custom-made intramedullary nails in repairing CSBD of the beagle femur. This effective strategy could provide an option to treat the clinical CSBD in weight-bearing bones.

Key words: 3D printing, Biphasic calcium phosphate ceramic, Graphene oxide, Segmental bone defect, Angiogenesis, Osteogenesis