Analysis of nanotubes formation (α-Fe2O3/Fe3O4) on the iron surface using anodic oxidation

Abstract

PurposeThis study aims to synthesize α-Fe₂O₃/Fe₃O₄ nanotube layers on pure iron via anodic oxidation and subsequent annealing, evaluating how temperature influences their morphology, wettability, degradation, and cellular response for biomedical applications.MethodsIron samples were anodized and annealed at temperatures from 150 °C to 400 °C. All samples were characterized for morphology, structure, and wettability. Based on this physical characterization, surfaces annealed at 350 °C and 400 °C were selected for further degradation tests in Hanks’ solution and biological evaluation with MC3T3-E1 pre-osteoblast cells. Biological assessment included cytotoxicity, cell adhesion assays, and qPCR analysis of genes related to integrin signaling (Integrin-β1, Integrin-α1, FAK, Src, Cofilin).ResultsThe annealing temperature directly affected the nanotube structure. The highest pore diameters and layer thicknesses were achieved at 350 °C and 400 °C, within overall ranges of 43–62 nm and 3–7 μm, respectively. These surfaces were superhydrophilic (contact angles < 5°) and showed an increased degradation rate during the initial immersion phase. Biologically, they supported cell adhesion without cytotoxicity and promoted the upregulation of genes in the integrin-FAK-Src-Cofilin pathway, indicating enhanced cytoskeletal dynamics.ConclusionAnodic oxidation with annealing at 350–400 °C produces superhydrophilic α-Fe₂O₃/Fe₃O₄ nanotube layers on iron. These surfaces enhance early-stage degradation and create a pro-adhesive environment by activating specific integrin-mediated signaling. This work paves the way for future research to optimize the stability and performance of these nanostructured iron-based materials for biodegradable medical devices.