## 1 Introduction  
Spinal cord injury (SCI), which involves dyssynergia and serious damage to motor and sensory functions in the human body, is often caused by trauma, dysfunction, or degenerative disease. Despite decades of therapeutic research, current treatments are limited to drug treatment in the acute stage or surgical methods [1, 2]. Additionally, the initial degree of impairment affects patients throughout life. Stem cell therapy is a promising strategy developed to treat SCI [3, 4, 5]. The transplanted stem cells promote neural and neural cord regeneration by providing a paracrine effect and a scaffold for replacing damaged neurons [6]. Recently, stem cell treatment has been suggested for radical SCI. Particularly, D1 Mesenchymal stem cells (MSCs) can cause auto-regeneration and differentiation of other mesenchymal systems and are used to restore cartilage in the orthopedic area [7]. Mesenchymal stem cells (MSCs) have recently been evaluated for use in cellular repair after central nervous system injury [8, 9]. MSCs are derived from the bone marrow and can self-renew and differentiate into several distinct mesenchymal lineages [10, 11, 12]. Through morphological and phenotypic changes, MSCsdifferentiate into neuron-like cells, making these cells a good candidate for use in tissue regeneration and treatment of nervous system injuries [13; 14].  
Super-paramagnetic iron-oxide nanoparticles (SPIONs) are composed of magnetite, which is an iron-oxide, and are thought to be next-generation nano-drugs. These particles are coated with a biocompatible polymer to enhance their stability and cell transfer effects [15; 16]. SPION-based drug delivery, nano-biomaterial, bio-imaging, and other methods are studied to determine their practical applications, and animal studies have been conducted to determine their potential in SCI therapy by using stem-cell-fusion to increase migration [17; 18]. However, further studies are needed before SPIONs can be applied clinically and to demonstrate the migration, stability, and safety by magnetic induction of stem cell fusions [19; 20]. Recent studies have focused, not only on improving biocompatibility and advancing magnetic materials, but also remotely controlling the magnetic field to cause SPIONs fusion [21]. Some research groups have reported risks such as cellular stress, gene expression changes, impacts on cell proliferation, and nanoparticle-protein interactions. Therefore, the cytotoxicity with nanoparticles should be further examined. Nano-materials could be improved to enable the safe use of SPIONs for developing new targeted therapies [22].  
In this study, we differentiated our work from the previous study using dopamine coating. Polydopamine is a mussel-inspired adhesive coating, which has become attractive in the biomaterials field due to its ability to form strong adhesive interactions with materials and with functional biomolecules that contain amine groups. The introduction of Polydopamine in SPION does not initiate any phase transfer in the bulk SPIONs since the Polydopamine polymerization influences the formation of the carbon layer on the surface rather than the bulk [23]. Herein, we report neuronal differentiation of MSCs and evaluate whether SPION-labeled MSCs could be magnetically targeted at the injury site to keeping the nature of MSCs under in vitro conditions [24].