Visible-light-responsive Au-coated NiTi-O nanotubes for enhancing osteogenic differentiation of human mesenchymal stem cells.

The biological performance of widely used nickel-titanium (NiTi) implants is strongly influenced by nanoscale surface characteristics. This study evaluated Au-coated NiTi-O nanotubes (ANT) as a visible-light-responsive osteogenic interface for human mesenchymal stem cells under 600 nm irradiation. NiTi-O nanotubes were fabricated by anodic oxidation followed by Au sputter coating, which preserved the open nanotubular morphology. Live/dead and MTT assays demonstrated that nanotube fabrication, Au coating, and 600 nm irradiation showed excellent biocompatibility. Under osteogenic conditions, 600 nm irradiation increased ALP activity, particularly on nanotubular surfaces. Among all experimental groups, the 600 nm-irradiated Au-coated nanotube surface showed the highest OPN, OCN, and BSP-2 expression, with the greatest matrix mineralization at 3 weeks. HSP27 and HSP70 were also elevated, consistent with mild photothermal adaptation associated with enhanced visible-to-near-infrared absorption in ANT near 600 and 780 nm. YAP nuclear localization and F-actin organization were primarily associated with nanotopography, whereas irradiation additionally stimulated HSP-related responses. Two-way ANOVA showed an irradiation effect on ALP activity at 1 week, while both surface and irradiation effects were evident at later endpoints. Significant interactions were observed only for ALP (2 weeks), OCN, HSP27, and HSP70. Mineralization showed additive, non-interacting surface (P < 0.0001) and irradiation effects (P = 0.0010). Collectively, these findings suggest that ANT promotes osteogenic differentiation through nanotopographical and photothermal mechanisms that interact at the level of ALP, OCN, and HSP responses but contribute additively to terminal mineralization.