Electrochemical reduction as a method to engineer black titania nanotube arrays with enhanced antibacterial and cytocompatible properties

Black titania nanotube arrays (TiO₂ NTAs) were produced using a two-step electrochemical method. This process aimed to narrow the bandgap of the material to increase visible light absorption and promote structural defects such as Ti³⁺ ions and oxygen vacancies (V_O). Cathodic polarization successfully reduced the bandgap from ⁓ 3.2 to ⁓ 2.9 eV while preserving the anatase structure of TiO₂, and suggested the presence of Ti³⁺- and V_O-related defects on the surface. Both normal and black nanotube-coated surfaces significantly inhibited bacterial growth. Under illuminated and dark conditions used in this study, black TiO₂ did not exhibit a statistically significant antibacterial advantage over normal TiO₂, and the observed antibacterial effect was largely attributed to nanotopography. Additionally, in vitro cytotoxicity tests with SAOS-2 cells revealed that black TiO2 NTAs significantly increased cell viability and adhesion to the surface. These results suggest that these defect-engineered black TiO₂ NTAs, hold promising potential for biomedical applications.