Cytocompatibility and Bone-Formation Potential of Se-Coated 316L Stainless Steel with Nano-Pit Arrays

316L stainless steel is still widely applied in joint replacement and orthopedic surgery due to its mechanical properties, corrosion resistance and relatively low price. In this study, electrochemical oxidation and nanoscale coating were used to fabricate Se-coated 316L stainless steel with nano-pit arrays to enhance its surface characteristics, biocompatibility and osseointegration ability. The modified 316L stainless steel was tested via field emission scanning microscopy (FESEM), energy-dispersive X-ray spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and Se release studies. The results of this study showed that the nano-pit arrays were 50 nm in diameter and that the Se coating consisted primarily of elemental Se and exhibited sustained release. The biological response of the samples was evaluated using in vitro rat bone marrow mesenchymal stem cell (rBMSCs) experiments and in vivo animal experiments. The modified 316L stainless steel displays enhanced abilities of cell adhesion, proliferation and osteogenic activity, as shown by FESEM, CCK-8 assay, immunofluorescence microscopy (IF) and alkaline phosphatase (ALP) activity assay in vitro and additional new bone formation in vivo, indicating its outstanding cytocompatibility and osteogenic differentiation ability. More importantly, the Se coating can upregulate gene expression of OPN, RUNX-2 and ALP, indicating that the nano-Se-coated 316L stainless steel with nano-pit arrays is a promising biomedical material for implants in orthopedic or dental clinic applications.