Abstract: BACKGROUND: Bone tissue has the function of self-renewal, reconstruction and repair of tissue defects. However, when a large area of severe bone defect occurs, bone grafts or bone substitutes are often needed to reconstruct the defect, which increases the risk of bone infection around the implant. 
OBJECTIVE: To prepare nanohydroxyapatite/polycaprolactone composite nanofiber scaffolds with different silver concentrations to determine the silver concentration that promotes cell proliferation and has antibacterial properties. 
METHODS: Nanohydroxyapatite/polycaprolactone composite nanofiber scaffolds with different silver concentrations (0, 0.001, 0.01, 0.1 mol/L) were prepared by using electrospinning technology. The microscopic morphology and elemental composition of scaffolds of four groups were shown by scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscope. MC3T3-E1 osteoblasts were co-cultured with four groups of scaffolds to study the effect of sample scaffolds on the cell proliferation and osteogenic differentiation. Four groups of scaffolds were co-cultured with Staphylococcus aureus (ATCC25923) and Escherichia coli (ATCC25922) to study the antibacterial properties of scaffolds by the formation of antibacterial circle and antibacterial rate.
RESULTS AND CONCLUSION: (1) Scanning electron microscopy showed that the four groups of electrospinning films were more continuous and uniform in diameter. The electrospinning filaments displayed a mesh-like structure, in which pore structures of different sizes were dispersed. As the silver-loaded content of the scaffold increased, the diameter of the nanofibers gradually increased. Transmission electron microscope showed that the silver-loaded scaffold nanofibers were uniformly dispersed with black silver nanoparticles, and the particle size diameter was (46±24) nm. (2) CCK-8 assay showed that compared with the unloaded silver scaffolds, silver-loaded 0.001, 0.01 mol/L nanofiber scaffolds could promote osteoblast proliferation. Silver-loaded 0.1 mol/L nanofiber scaffolds inhibited osteoblast proliferation. Nucleus and cytoskeleton staining showed that silver-loaded 0, 0.001, and 0.01 mol/L nanofiber scaffolds facilitated the extension of osteoblast morphology. Silver-loaded 0.1 mol/L nanofiber scaffolds were not conducive to the extension of osteoblast morphology. (3) Alkaline phosphatase staining showed that silver-loaded 0, 0.001, and 0.01 mol/L nanofiber scaffolds were beneficial to osteoblast differentiation, and silver-loaded 0.1 mol/L nanofiber scaffolds inhibited osteoblast differentiation. (4) Antibacterial circle experiment showed that the unloaded silver scaffolds had no antibacterial properties. As the silver-loaded content of the scaffold increased, the antibacterial properties of silver-loaded scaffolds increased. Antibacterial rate experiment proved that silver-loaded 0.01 mol/L nanofiber scaffolds had strong antibacterial activity. (5) The results confirm that the silver-loaded 0.01 mol/L nanohydroxyapatite/polycaprolactone composite nanofiber scaffold has both good biological activity and excellent antibacterial properties. 

Key words: electrospinning, nanofiber, nanohydroxyapatite, silver nanoparticle, bone infection, osteogenesis, antibacterial property