Abstract: BACKGROUND: Bone morphogenetic protein 2 is vital in embryonic development, bone formation, and regeneration, but its high-dose application is linked to cancer. Bone morphogenetic protein 2 osteogenic peptide L20 reduces adverse effects like cancer and boosts bone tissue regeneration. 
OBJECTIVE: To graft bone morphogenetic protein 2 active peptide segments onto mesopores and surfaces through a peptide mimicry strategy inspired by oysters, and explore its impact on osteogenic properties of tissue-engineered bone.
METHODS: (1) Mesoporous bioactive glass was synthesized using a template method. Bone morphogenetic protein 2 osteogenic peptide L20 was loaded onto mesoporous bioactive glass using a one-step synthesis method to characterize the morphology and in vitro sustained release properties of mesoporous active glass nanoparticles loaded with bone morphogenetic protein 2 osteogenic active peptide L20. (2) Bone marrow mesenchymal stem cells were isolated and extracted from SD rats. After two generations, they were co-cultured with PBS (blank group), mesoporous bioactive glass nanoparticles (control group), and mesoporous bioactive glass nanoparticles loaded with bone morphogenetic protein 2 osteogenic active peptide L20 (experimental group). Cell live/dead fluorescence staining and CCK-8 assay were used to detect cytotoxicity and cell proliferation. Scanning electron microscopy was used to observe cell adhesion. After osteogenic induction and differentiation, alkaline phosphatase staining, Alizarin red S staining, and osteogenesis-related gene expression were detected. (3) Fifteen SD rats were selected to establish bilateral femoral condyle defect models and divided into three groups using a random number table method: the blank group (n=5) was not implanted with any material; the control group (n=5) was implanted with mesoporous bioactive glass nanoparticles, and the experimental group (n=5) was implanted with mesoporous bioactive glass nanoparticles loaded with bone morphogenetic protein 2 osteogenic active peptide L20. Eight weeks after surgery, femoral Micro-CT scanning and tissue morphology observation were performed. 
RESULTS AND CONCLUSION: (1) Scanning electron microscopy showed that the mesoporous bioactive glass nanoparticles loaded with bone morphogenetic protein 2 osteogenic active peptide L20 were spherical and monodisperse particles. Transmission electron microscopy showed their porous structure with an average particle size of (268.10±0.58) nm, which could release L20 in vitro. (2) Mesoporous bioglass nanoparticles loaded with bone morphogenetic protein 2 osteogenic active peptide L20 were non-cytotoxic and could promote the proliferation and adhesion of bone marrow mesenchymal stem cells. Compared with the blank group and the control group, the alkaline phosphatase activity and extracellular matrix mineralization capacity of the experimental group were increased (P < 0.05), and the mRNA expression levels of alkaline phosphatase, Runx2, and osteocalcin were increased (P < 0.05). (3) The results of femoral Micro-CT scanning showed that compared with the blank group and the control group, the new bone mass and bone density of the experimental group were increased (P < 0.05). The results of hematoxylin-eosin and Masson staining showed that compared with the blank group and the control group, the new bone formation and collagen fibers of the experimental group were increased. (4) These findings indicate that mesoporous bioactive glass loaded with bone morphogenetic protein 2 active peptide L20 exhibits excellent biocompatibility and in vitro and in vivo osteogenic properties, promoting regeneration and repair of SD rat femoral condyle defects. 

Key words: bone morphogenetic protein 2 osteogenic peptide, mesoporous bioactive glass, nanoparticle, catechol, osteoblast differentiation, femoral condyle defect, bone tissue engineering, biomaterials