Additively manufactured 316L stainless steel with improved corrosion resistance and biological response for biomedical applications

Abstract

Enhancing the corrosion resistance and improving the biological response to 316 L stainless steel is a long-standing and active area of biomedical research. Here, we analyzed the structure and corrosion tendency of selective laser melted-additively manufactured (AM) 316 L stainless steel (AM 316L SS) and its wrought counterpart. SEM analysis showed a fine (500–800 nm) interconnected sub-granular structure for the AM 316L SS, but a polygonal coarse-grained structure for the wrought sample. Relative to the wrought sample, the AM 316L SS also exhibited a higher charge transfer resistance and higher breakdown potential (˜1000 mV vs. SCE) when tested in biological electrolytes, which included human serum, PBS, and 0.9 M NaCl. A higher pitting resistance (extended passive region) and improved stability of the AM 316L SS was attributed to its dense structure of oxide film and refined microstructure. Finally, material compatibility with pre-osteoblasts was analyzed. Large cytoplasmic extension of osteoblast cells and retention of stiller morphology was observed when cells were cultured on the AM 316L SS as compared to its wrought counterpart, suggesting that the AM 316L SS was a better substrate for cell spreading and differentiation. The differentiation of cultured cells was further validated by western blot for Runx2. Runx2, an anti–proliferative marker indicative of differentiation, was equivalent in cells cultured on either samples, but overall more cells were present on the AM 316L SS. Given its higher corrosion resistance and ability to support osteoblast adherence, spreading and differentiation, the AM 316L SS has potential for use in the biomedical industry.