Hemocompatibility of plasma nitrided 316L stainless steel: Effect of processing temperature

Abstract The influence of plasma nitriding temperature on the hemocompatibility of 316LSS was evaluated through in vitro thrombogenicity tests. The nitriding processes were carried out using an industrial furnace at a temperature range that does not impair the corrosion resistance. The crystallographic phases, topography, chemical composition, wettability, and thrombogenicity of the modified surfaces were evaluated and compared to untreated 316LSS samples. The results revealed the formation and evolution of the γN phase with increasing the temperature. The γN phase development was assessed with the stacking fault probability, which rose with temperature leading to rougher surfaces. Nitrided samples at 380 ˚C exhibited polar groups at the surface, increasing the surface energy. There was a substantial reduction of these groups in samples nitrided at 400˚C and almost negligible at 420˚C. Lower amounts and less activation of platelets was observed on the nitrided surface at the lowest temperature, contrary to the results obtained at the highest nitriding temperature. It was correlated with the hydrophobicity and roughness of the plasma nitrided surfaces. Through this investigation it is possible to propose adequate conditions of plasma nitriding to improve the hemocompatibility of 316LSS samples, reinforcing the feasibility of this processing technique for biomaterials on an industrial-scale.