White and black anodic TiO2 nanotubes: Comparison of biological effects in A549 and SH-SY5Y cells

Nanoscale Topography of Anodic TiO2 Nanostructures Is Crucial for Cell–Surface Interactions

“…Electrochemical anodization is one of the most commonly used techniques for nanoscale surface modifications, due to its ease of use and nanoscale control, allowing the formation of nanostructures directly on Ti metal and its alloys. ,, To date, a variety of titanium dioxide (TiO 2 ) nanostructures can be fabricated as a function of the anodization parameters, including nanotubes (NTs , or single NTs dispersed by ultrasonication), nanopores (NPs), , nanochannels, , dispersed nanocylinders, and nanopillars . Through extensive investigation for decades, anodic TiO 2 nanotubes can offer excellent control over NT diameter in the sub-100 nm range (for an overview, see refs , , , , and ), and various nanotube morphologies such as nanotubes with a thin initiation layer, open-top nanotubes, single-wall or double-wall morphology, multilayers, and spaced nanotubes have been developed. , In addition, the nanostructured surfaces can be also modified for targeted biomedical applications, in terms of (i) additional bioactive layers, e.g., hydroxyapatite with a subsequent deposition step or via a one-step process based on microarc oxidation, , or hydrothermal based treatments, (ii) coated with various inorganic or organic layers (TiO 2 , organic monolayers), (iii) decorated with various nanoparticles, (iv) functionalized with organic molecules, peptides, drugs, etc., (v) via various annealing treatments. , Such modifications can further increase the cell activity and increase osseointegration or antibacterial activity of the various TiO 2 nanostructured layers, as well as influencing the TiO 2 NT/cell interface …”

“…2,23 In addition, the nanostructured surfaces can be also modified for targeted biomedical applications, in terms of (i) additional bioactive layers, e.g., hydroxyapatite with a subsequent deposition step or via a one-step process based on microarc oxidation, 33,34 or hydrothermal based treatments, 35 (ii) coated with various inorganic or organic layers (TiO 2 , 36 organic monolayers 37 ), (iii) decorated with various nanoparticles, 38 (iv) functionalized with organic molecules, peptides, drugs, etc., 39 (v) via various annealing treatments. 40,41 Such modifications can further increase the cell activity and increase osseointegration or antibacterial activity of the various TiO 2 nanostructured layers, as well as influencing the TiO 2 NT/cell interface. 42 Regarding the impact of the NT's morphology on cell interactions, literature data show that this depends on the cell plating density (5 × 10 3 to 5 × 10 4 or even higher) on the surface of the sample (and on the sterilization procedure), 43−45 with lower cell plating densities (e.g., 5 × 10 diameters below 30 nm are optimal and for higher densities or changes in the tube morphology or properties (due to sterilization), it is larger tube diameters.…”