Intrinsically ferromagnetic Fe-doped TiO2 coatings on titanium for accelerating osteoblast response in vitro

The microenvironment can regulate osteoblast behavior during integration of implants with host bones. An intrinsically magnetic field induced by an Fe³⁺ doped TiO₂ coating was applied herein to enhance the cytocompatibility of Ti. Porous TiO₂ incorporated with different amounts of Fe (2.27-11.07 wt%) was directly prepared on Ti by micro-arc oxidation. The microstructure, roughness, wettability, ion releasing and magnetic property of TiO₂ coatings were investigated. Cell behavior, including adhesion, proliferation, differentiation, collagen secretion and extracellular matrix mineralization on coating surfaces was evaluated. The results show that incorporation of Fe³⁺ did not significantly alter the phase component, topography, roughness and wettability of coatings, and with increased doses of Fe³⁺, trace amounts of Fe³⁺ were released into the media, whereas the CA²⁺ accumulation concentration slightly decreased. Fe-Doped TiO₂ displayed a weak ferromagnetic property, and its saturation magnetization value increased initially and then decreased with the increased dose of Fe. Compared with the undoped, proliferation, expression of osteogenesis-related genes, collagen secretion and extracellular matrix mineralization of osteoblasts were enhanced with Fe doped ones, especially for those with 4.25 wt% Fe. By analyzing the structures and properties of different surfaces and their osteoblast responses, it is deduced that the ferromagnetism of Fe doped TiO₂ plays a key role in enhancing osteoblast behavior. Such a result provides a new perspective for the potential application of ferromagnetic coatings in bone repair.