Objective To investigate the role of three-dimensional scaffolds seeded with NeuroD1-modified neural stem cells (NSCs) for repair of spinal cord injury in rats.Methods A new three-dimensional bio-printer was used to make bionic spinal cord scaffolds.NSCs are transduced with retrovirus vectors encoding NeuroD1 to express transgenes in high levels.Forty healthy female SD rats were divided into control group,scaffold group,scaffold + NSCs-green fluorescent protein (GFP) group and scaffold + NSCs-NeuroD1 group with 10 rats per group,according to the random number table.Spinal cord injury in rats was induced using the electric controlled cortical impactor.A week later,the control group was excised 3 mm spinal cord at the injury site under microscope.RT-PCR was used to confirm the construction of NeuroD1 overexpressing NSCs.Survival and differentiation of transplanted NSCs were detected with fluorescent staining.Rat neurological motor function was evaluated with BBB score at postoperative 1,2,4,6 and 8 weeks.Rat electrophysiological changes were observed by monitoring motion evoked potential and sensory evoked potential at 8 weeks.Results RT-PCR results confirmed the successful reconstruction of NeuroD1-overexpressing NSCs.BBB score in scaffold + NSCs-NeuroD1 group was the highest and had significant differences compared to other three groups (P ＜ 0.05).Electrophysiological results showed the motor and sensory in scaffold + NSCs-NeuroD1 group had the shortest latencies and highest amplitudes,which revealed significant differences compared to other three groups (P ＜0.05).Immunofluorescence staining showed GFP cells in scaffold + NSCs-NeuroD1 group at 8 weeks,which differentiated into neurons and astrocytes.GAP-43 was positively stained,and myelin formation was detected.Conclusion Three-dimensional scaffolds seeded with NeuroD1-modified NSCs can promote nerve loop reconstruction in spinal cord injury rats,and accelerate recovery of motor and sensory function.