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Titanium and titanium alloy implants that have been demonstrated to be more biocompatible than other metallic implant materials, such as Co-Cr alloys and stainless steels, must also be accepted by bone cells, bonding with and growing on them to prevent loosening. Highly ordered nanoporous arrays of titanium dioxide that form on titanium surface by anodic oxidation are receiving increasing research interest due to their effectiveness in promoting osseointegration. The response of bone cells to implant materials depends on the topography, physicochemistry, mechanics, and electronics of the implant surface and this influences cell behavior, such as adhesion, proliferation, shape, migration, survival, and differentiation; for example the existing anions on the surface of a titanium implant make it negative and this affects the interaction with negative fibronectin (FN). Although optimal nanosize of reproducible titania nanotubes has not been reported due to different protocols used in studies, cell response was more sensitive to titania nanotubes with nanometer diameter and interspace. By annealing, amorphous TiO2 nanotubes change to a crystalline form and become more hydrophilic, resulting in an encouraging effect on cell behavior. The crystalline size and thickness of the bone-like apatite that forms on the titania nanotubes after implantation are also affected by the diameter and shape. This review describes how changes in nanotube morphologies, such as the tube diameter, the thickness of the nanotube layer, and the crystalline structure, influence the response of cells.

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Valve metals such as titanium (Ti), zirconium (Zr), niobium (Nb) and tantalum (Ta) that confer a stable oxide layer on their surfaces are commonly used as implant materials or alloying elements for titanium-based implants, due to their exceptional high corrosion resistance and excellent biocompatibility. The aim of this study was to investigate the bioactivity of the nanostructures of tantala (Ta2O5), niobia (Nb2O5), zirconia (ZrO2) and titania (TiO2) in accordance to their roughness and wettability. Therefore, four kinds of metal oxide nanoporous and nanotubular Ta2O5, Nb2O5, ZrO2 and TiO2 were fabricated via anodization. The nanosize distribution, morphology and the physical and chemical properties of the nanolayers and their surface energies and bioactivities were investigated using SEM-EDS, X-ray diffraction (XRD) analysis and 3D profilometer. It was found that the nanoporous Ta2O5 exhibited an irregular porous structure, high roughness and high surface energy as compared to bare tantalum metal; and exhibited the most superior bioactivity after annealing among the four kinds of nanoporous structures. The nanoporous Nb2O5 showed a uniform porous structure and low roughness, but no bioactivity before annealing. Overall, the nanoporous and nanotubular layers of Ta2O5, Nb2O5, ZrO2 and TiO2 demonstrated promising potential for enhanced bioactivity to improve their biomedical application alone or to improve the usage in other biocompatible metal implants.

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The morphology and the physical and chemical characteristics of four groups of TiO2-ZrO2-ZrTiO4 nanotubes that were fabricated via anodization in a non-aqueous electrolyte were investigated in order to examine their influence on the bioactivity of, and cell adhesion on, Ti50Zr alloy. Scanning electron microscopy (SEM) and 3D profilometry were used for the characterization. The in vitro cell responses to nanotubular surfaces with different inner diameters (Di) between 25 and 49 nm were assessed using osteoblast cells (SaOS2). The results of the MTS assay indicated that the percentage of cell adhesion on the nanotubes was influenced by the nanoscale topographical parameters including the tube inner diameter (Di), the tube wall thickness (Wt), the amplitude roughness (Sa) and the spacing roughness (Sm) of the nanotubular surface. Cell adhesion was promoted to 84.9% on nanotubes with an inner diameter of 25 nm, or 80.3% on nanotubes with a large wall thickness of 34 nm due to the accelerated integrin clustering and focal contacts of formation. A nanotubular surface with a low spacing roughness of 33 nm(3) nm(-2) led to a cell adhesion of 61.0%. Similarly, a nanotubular surface with a high amplitude roughness of 1.03 μm revealed a cell adhesion of 61.5% in instances where the inner diameters (29 nm) and wall thicknesses (24 nm) were within the critical dimensional parameters for cells to survive and thrive.

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