Osteoblast cell response to oxide films formed on nanograin 316L stainless steel obtained by two-dimensional linear plane-strain machining

• Linear plane-strain machining is proposed to prepare ultra-fine grained substrates.
• Surface oxide chemistry does not change by refining the average grain size.
• Spontaneous oxide on ultra-fine grained substrates improves the biocompatibility.

The long-term success of orthopedic implants is strongly determined by their surface characteristics and the interaction of this surface with the surrounding biological environment. The biocompatibility of metallic biomaterials is mainly due to their ability to form an adherent oxide layer on their surface that is in direct contact with the biological environment. In this study, oxide layers were grown on ultra-fine grained 316L stainless steel samples, naturally, chemically and thermally. Samples in three different nanoscale average grain sizes were obtained by severe plastic deformation using linear plane-strain machining technique. Refining the grain size along with growing the oxide layer create surfaces with a wide variety of surface topography, roughness and chemistry. After chemical treatment, a chromium-enriched oxide with island-like topography was formed on the surface and substrates with smaller average grain size demonstrated rougher surfaces. After thermal treatment, micro-scaled oxide grains were formed on the surface and the amount of manganese oxide in its composition was increased. MC3T3 cell adhesion was greatly improved on the native oxide formed on the sample with the smallest average grain size. The oxide layer that is naturally formed on the surface demonstrated higher biocompatibility compared to both thermally and chemically formed oxides.