On the Use of Black Ti as a Bone Substituting Biomaterial: Behind the Scenes of Dual-Functionality

Despite the potential of small-scale pillars of black titanium (bTi) for killing the bacteria and directing the fate of stem cells, not much is known about the effects of the pillars' design parameters on their biological properties. Here, three distinct bTi surfaces are designed and fabricated through dry etching of the titanium, each featuring different pillar designs. The interactions of the surfaces with MC3T3-E1 preosteoblast cells and Staphylococcus aureus bacteria are then investigated. Pillars with different heights and spatial organizations differently influence the morphological characteristics of the cells, including their spreading area, aspect ratio, nucleus area, and cytoskeletal organization. The preferential formation of focal adhesions (FAs) and their size variations also depend on the type of topography. When the pillars are neither fully separated nor extremely tall, the colocalization of actin fibers and FAs as well as an enhanced matrix mineralization are observed. However, the killing efficiency of these pillars against the bacteria is not as high as that of fully separated and tall pillars. This study provides a new perspective on the dual-functionality of bTi surfaces and elucidates how the surface design and fabrication parameters can be used to achieve a surface topography with balanced bactericidal and osteogenic properties.