Abstract: Abstract: Objective To investigate the mechanism of inorganic bone regeneration material silicon-containing hydroxyapatite (si-HA) in promoting the proliferation and osteogenic differentiation of mouse pre-osteoblast MC3T3-E1 (3T3) by regulating the polarity conversion of macrophages. Methods The hydroxyapatite (HA) and si-HA nanoparticles were prepared, and were used to stimulate RAW264.7 macrophages of mice at a dose of 10 mg/L. The cells were divided into HA group and si-HA group. Another control group (DMEM medium with 10% FBS) was set. The polarization status and the expression level of inflammatory factors in RAW cells were analyzed. The supernatants of RAW cells stimulated by HA and si-HA nanoparticles for 3 days were collected to prepare RAW conditioned medium, HA + RAW conditioned medium and si-HA + RAW conditioned medium. The conditioned medium was used to culture mouse 3T3 preosteoblasts, with complete medium as the blank control group. The expression levels of proliferation and osteogenic related genes were detected. Results The results showed that the expression levels of macrophage M1 phenotype factor iNOS, TNF-α and IL-1β mRNA were significantly down-regulated in si-HA group compared with those of the control group and HA group. The expression levels of Arginase, IL-10 and IL-1ra mRNA were significantly higher in si-HA group compared with those of the control group and HA group (P＜0.05). The expression level of IL-6 mRNA was lower in HA group (P＜0.05). The proliferation ability, alkaline phosphatase (ALP) activity and mineralized nodule formation of 3T3 cells were significantly stronger in si-HA+RAW group than those in the control group, RAW group and HA+RAW group (P < 0.05). After 14 days of culture, the expression levels of ALP, OCN, OPN, Col-l and Runx2 mRNA were significantly higher in si-HA+RAW group than those of the other three groups (P < 0.05). Conclusion The results show that si-HA nanoparticles can induce a favorable bone immune microenvironment, enhance the proliferation and osteogenic differentiation of 3T3 cells.

Key words: macrophage activation, osteoblasts, silicon, hydroxyapatites, bone immunity, osteogenic differentiation