Surface Adhesion Properties and Cytotoxicity of Graphene Oxide Coatings and Graphene Oxide/Silver Nanocomposite Coatings on Biomedical NiTi Alloy

Graphene has potential biomedical applications; thus, its surface adhesion is important. In this study, graphene oxide (GO) coatings and graphene oxide/silver (GO/Ag) nanocomposite coatings were developed on NiTi alloy and the surface structure surface adhesion, mechanical properties, and cytotoxicity of the coatings were evaluated. The coatings were developed using electrophoretic deposition (EPD) at 30 V with coating times of 1, 5, and 10 min. The GO-coated and the GO/Ag-coated NiTi alloys were characterized using scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy, and atomic force microscopy (AFM). The surface adhesion force and energy of the coating were measured using the AFM tapping mode and its mechanical properties (hardness and Young's Modulus) were investigated. The cytotoxicity of the coatings on human gingival fibroblasts was determined using a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. The thickness of the GO coatings on the NiTi alloy ranged from 0.34 to 1.32 mu m and the thickness of the GO/Ag coatings ranged from 0.48 to 1.38 mu m. The coating thickness and surface roughness (Ra) increased as coating time increased from 1 to 10 min. The GO and the GO/Ag coatings had adequate surface adhesion forces, and the 1-min coatings of GO and GO/Ag had the highest surface adhesion forces (14.86 and 15.33 nN, respectively). The hardness of the GO coatings ranged from 0.41 to 0.88 GPa, and that of the GO/Ag coatings ranged from 0.44 to 0.92 GPa. The Young's modulus of the GO and the GO/Ag coatings ranged from 1.13 to 4.25 GPa, and 1.15 to 4.89 GPa, respectively. The coatings showed favorable surface adhesion, mechanical properties and good biocompatibility with high cell viability of the human gingival fibroblasts. Therefore, the GO-coated and the GO/Ag-coated NiTi alloys can be used for biomedical applications.