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

Abstract The osteoblast‐function associated integrin–ligand interactions are known to be dependent on divalent cations, but there is scarce information about the effect of Ca²⁺ and Mg²⁺ adsorption properties of an implant surface on integrin α₅β₁–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 MnO₂ 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 [MnO₆] layers possess the highest V_Mn content, which is determined by the ratios of Mn³⁺/Mn⁴⁺ and K/Mn. The increased V_Mn content enhances the Ca²⁺ and Mg²⁺ adsorption properties of the birnessite coatings. When immersed in Ca²⁺/Mg²⁺ 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 α₅β₁‐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.