Background We previously showed that nano-hydroxyapatite/carboxymethyl chitosan (n-Ha/CMCS) displayed excellent mechanical properties,good degradation rates and exceptional biocompatibility,with negligible toxicity.The aim of this study was to determine the effect of the same composite with vascular endothelial growth factor (VEGF)-transfected bone marrow stromal cells (BMSCs) in a rabbit radial defect model.Methods The nano-hydroxyapatite was produced through co-precipitation.The n-HA/CMCS scaffold was produced by particle filtration and lyophilization followed by genipin crosslinking.Total RNA from rabbit bone was reverse-transcribed to synthesize VEGF165-pcDNA3.1 that was transfected into the BMSCs.The composite was implanted into a rabbit radial defect model,and the osteogenic activity examined by gross morphology,X-ray examination and hematoxylin and eosin (HE) staining.Results The microstructure and mechanical property of the n-HNCMCS scaffold resembled natural cancellous bone.Compared with glutaric dialdehyde crosslinked scaffolds,the genipin crosslinked scaffold was less toxic,and displayed a higher capacity to promote cell adhesion and proliferation.Spontaneous fluorescence of the composite permitted visualization of the composite-bone interface and the adhesion behavior of cells on the scaffold under laser scanning confocal microscopy.The scaffold with VEGF-transfected BMSCs bridged the bony defect and promoted healing,with most of the implanted material being replaced by natural bone over time with little residual implant.Using X-ray,we noted obvious callus formation and recanalization of the bone marrow cavity.Furthermore,HE stained sections showed new cortical bone formation.Conclusions The n-HA/CMCS scaffold composite with VEGF-trasnfected BMSCs is biocompatible,nontoxic,promotes the infiltration and formation of the microcirculation,and stimulates bone defect repair.Furthermore,the degradation rate of the composite matched that of growing bone.Overall,this composite material is potentially useful for bone defect repair.