β-FeOOH/Fe-TiO heterojunctions on Ti for bacteria inactivation under light irradiation and biosealing.

Intraosseous transcutaneous implants transferring mechanical stress directly from the skeleton to a prosthesis are an area of biological mechanics. However, bacterial invasion and weak biosealing with skin tissue usually induce implant failure. In this paper, composite coatings consisting of β-FeOOH as an outer layer and Fe-TiO as an inner layer were prepared on Ti via micro-arc oxidation and hydrothermal treatment (HT). The surface microstructures and optical absorption properties of the coatings were observed, the production of reactive oxygen species (ROS) was measured, Staphylococcus aureus (S. aureus) and fibroblast behaviors were studied in vitro, and bacteria inactivation and skin tissue responses on different surfaces were evaluated in vivo. The results show that Fe was doped into TiO and β-FeOOH nanoparticles were gradually deposited on TiO during HT treatment, forming β-FeOOH/Fe-TiO heterojunctions. The light absorption of the composite coatings shifted to the longer wavelength region because of a narrowed TiO bandgap and the formation of heterojunctions. Under light irradiation, photoinduced electrons and holes on the heterojunctions were separated efficiently. Via optimizing the amount of Fe in TiO, ROS that formed at the heterojunctions after light irradiation for 10 min could kill 80% of S. aureus compared with pure Ti in vitro, but they did not affect fibroblast behavior, including proliferation and phenotyping. In vivo, the optimized β-FeOOH/Fe-TiO heterojunctions, upon light irradiation, could inhibit bacterial infection, suppress an inflammatory response, and promote integration with skin tissue. Such results provide a new perspective suggesting the potential application of β-FeOOH/Fe-TiO heterojunctions in percutaneous Ti implants, especially in infected cases.