Controlling Preosteoblast Behavior through Manganese Vacancy-Rich Birnessite with Enhanced Divalent Cation Modulation of Fibronectin–Integrin Interactions

The osteoblast-function associated integrin–ligand interactions are known to be dependent on divalent cations, but there is scarce information about the effect of Ca 2+ and Mg 2+ adsorption properties of an implant surface on integrin α 5 β 1 –fibronectin interactions and the subsequent osteoblast behavior. Cation adsorption properties are closely associated with the extent of structural defects in materials. Here, the birnessite-type MnO 2 coatings with different amounts of manganese vacancy ( V Mn ) are prepared on Ti substrates via hydrothermal treatment (denoted as 1M100-Ti, 5M100-Ti, and 5M120-Ti). The 5M120-Ti surface with hierarchical flower-like structure and the most stacked [MnO 6 ] layers possess the highest V Mn content, which is determined by the ratios of Mn 3+ /Mn 4+ and K/Mn. The increased V Mn content enhances the Ca 2+ and Mg 2+ adsorption properties of the birnessite coatings. When immersed in Ca 2+ /Mg 2+ aqueous solution, the birnessite coatings significantly promote fibronectin adsorption and the exposure of cell-binding domains on adsorbed fibronectin with 5M120-Ti showing the greatest enhancement. Accordingly, the 5M120-Ti surface provides more α 5 β 1 -integrin-specific instructions to MC3T3-E1 preosteoblasts capable of enhancing spreading and osteoblastic differentiation compared to two other samples. This study may provide a prospective approach of modulation of integrin–ligand interactions for controlling cell behavior by adjusting metal vacancies in metal oxides coatings.