Abstract: BACKGROUND: The biomimetic periosteum synthesized by mesoporous bioactive glass nanoparticles and methacrylic acid gelatin can release calcium, silicon and phosphorus ions in the local area of bone defect and promote osteogenesis. However, silicon ions can also regulate the polarization of macrophages, so the effect of bionic periosteum on local inflammatory microenvironment of bone defect still needs to be explored. 
OBJECTIVE: To explore the relationship between the regulation of inflammatory microenvironment and the promotion of bone repair by inorganic ion biomimetic periosteum in vivo and in vitro. 
METHODS: (1) In vitro: The bionic periosteum was obtained by photocrosslinking mesoporous bioactive glass nanoparticles and methacrylic acid gelatin. Inductively coupled plasma spectroscopy was used to observe the release of Si4+ from biomimetic periosteum within 7 days. Bone marrow mesenchymal stem cells were inoculated into methacrylic acid gelatin hydrogel and mesoporous bioactive glass nanoparticles/methacrylic acid gelatin composite hydrogel separately. With the simple cultured cells as control, the biocompatibility of the cells was detected by Live/Dead fluorescence staining. Bone macrophages were inoculated in methacrylic acid gelatin hydrogel and mesoporous bioactive glass nanoparticles/methacrylic acid gelatin composite hydrogel separately. With simple cultured cells as control, the effect of bionic periosteum on macrophage phenotype in vitro was detected by nitric oxide synthase (macrophage M1 phenotype) and CD206 (macrophage M2 phenotype) immunofluorescence staining. (2) In vivo: The rat model of skull defect was established, and methacrylic acid gelatin hydrogel and mesoporous bioactive glass nanoparticles/methacrylic acid gelatin hydrogel were implanted into the bone defect. The local macrophage phenotype of bone defect was detected by RT-PCR at 7 days after operation, and the osteogenic property of biomimetic periosteum was detected by hematoxylin-eosin staining at 8 weeks after operation. 
RESULTS AND CONCLUSION: (1) In vitro: The bionic periosteum released Si4+ to the maximum concentration within 24 hours, and released slowly within 6 days after that. After co-culture for 3 days, Live/Dead fluorescence staining showed that the bone marrow mesenchymal stem cells in each group grew well, had good cell activity, and had no obvious death. After co-culture for 7 days, the results of immunofluorescence staining showed that most of the macrophages in the bionic periosteum group were M2, while those in the methacrylic acid gelatin group and control group were M1. After co-culture for 7 days, the results of alkaline phosphatase staining showed that the staining in the bionic periosteum group was stronger than that in the control group and the methacrylic acid gelatin group. (2) In vivo: RT-PCR results showed that most of the macrophages in the local inflammatory microenvironment of the bone defect of the rats implanted with bionic periosteum were M2, while most of the macrophages in the blank group and the methacrylic acid gelatin group were M1. Hematoxylin-eosin staining showed that there were more new bones in the bionic periosteal group than in the blank group and the methacrylic acid gelatin group. (3) The results showed that the inorganic ion bionic periosteum promoted the M2 polarization of macrophages in the inflammatory region through the release of Si4+, which could inhibit inflammation and promote osteogenesis. 

Key words: inorganic ion, bionic periosteum, inflammation, macrophage, osteogenesis, immune microenvironment