Antibacterial activity and surface characteristics of nanotube-formed Ti–xNb–Ag–Pt alloy.

In general, Ti alloys are commonly used as biomaterials for implants. However, in the case of such alloys, the high elastic modulus causes stress shielding effects and bacterial growth, reducing their biocompatibility. In order to improve it, new alloys composed of Ti–Nb–Ag–Pt were developed in this study because it is possible to reduce the elastic modulus by adding an alloying element, such as Nb, and to reduce the bacterial activity by adding Ag and Pt elements. The following studies were conducted with the aim of manufacturing and forming nanotubes on the surface to greatly improve the biocompatibility. Ti–xNb–Ag–Pt alloys were manufactured using a vacuum arc furnace in an Ar atmosphere, homogenized for 1 h at 1050 °C, and then quenched at 0 °C. The formation of nanotubes on the surfaces of the alloys was performed using the anodization method with an applied voltage of 30 V in 1 M H₃PO₄ + 0.8 wt% NaF for 1 h at 25 °C. The formed nanotube surfaces were analyzed by optical microscopy, field emission scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, nanoindentation tests, and antibacterial tests. Antibacterial activity was evaluated according to the ISO 22196:2007 method, for which S. aureus (NBRC122135) was used. The microstructure of Ti–10Nb–Ag–Pt was a needle-like structure, and Ti–50Nb–Ag–Pt presented both an equiaxed structure and a needle-like structure. The size of the nanotube diameter decreased as the Nb content increased. The Ag and Pt elements were evenly distributed on the nanotube-formed alloy surfaces. The Vickers hardness and the elastic modulus value decreased as the Nb content increased. Following the nanotube formation, the Vickers hardness and elastic modulus values decreased by thrice, and only the nanotube-formed Ti–xNb alloys containing Ag and Pt showed the antibacterial activity effect. [ABSTRACT FROM AUTHOR]