Abstract: BACKGROUND: The bone scaffold with complex porous structure can be customized accurately and individually by additive manufacturing technology, so as to achieve the dual bionics of the structure and function of cancellous bone at critical-sized bone defects.
OBJECTIVE: To clear the mechanical properties and biological activity of β-tricalcium phosphate bioceramic bone scaffold with triply periodic minimal surface structure, and reveal the regulatory effect of triply periodic minimal surface structure on osteoblasts through material and cytological characterizations. 
METHODS: Three kinds of triply periodic minimal surface G surface structure β-tricalcium phosphate bioceramic bone scaffolds with different pore sizes of 330, 420, and 510 μm were designed by Matlab R2020a software, and the design drawings were analyzed by Inspire 2018 software. The STL file exported based on the triply periodic minimal surface structure was the blueprint. β-Tricalcium phosphate scaffolds were fabricated by additive manufacturing technology based on digital laser processing. The surface morphology was observed by scanning electron microscope. The phase composition was detected by X-ray diffractometer, and the mechanical strength was detected by universal material testing machine. MC3T3-E1 cells were co-cultured with scaffolds. Cell proliferation, cell adhesion, and alkaline phosphatase activity were detected.   
RESULTS AND CONCLUSION: (1) Inspire 2018 software showed that triply periodic minimal surface presented a smooth, continuous and uniform porous structure. (2) Scanning electron microscope confirmed that the additive manufacturing technology based on digital laser processing successfully realized the accurate molding of triply periodic minimal surface structure. (3) X-ray diffraction confirmed that the scaffold was composed of pure β-tricalcium phosphate crystal phase. (4) The compressive strength and elastic modulus of the three groups of scaffolds were all within or near the range of cancellous bone, and the compressive strength of the scaffolds was inversely proportional to the pore size. (5) CCK8 assay showed that MC3T3-E1 cells grew well on the scaffolds; the biological activity of the scaffolds was dose-dependent with the pore size; and the 510 μm pore diameter scaffold had the best effect on promoting proliferation. (6) Living cell imager and laser confocal microscope showed that MC3T3-E1 cells could adhere to the scaffold in the early stage, and the amount of adhesion increased with the increase of pore size. (7) Alkaline phosphatase activity analysis showed that the alkaline phosphatase activity of cells on 420 μm scaffold was the highest. (8) The results show that the mechanical properties and biological activity of the triply periodic minimal surface structure β-tricalcium phosphate bioceramic scaffold are excellent; the pore size of 420 μm is beneficial to cell differentiation and 510 μm is beneficial to cell proliferation, which has the potential to repair critical bone defects.

Key words: triply periodic minimal surfaces, bioceramic, β-tricalcium phosphate, additive manufacturing, digital laser processing, critical-sized bone defect, pore size, MC3T3-E1 cell