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Surface modification of dental implants or orthopedic implants is important for biocompatibility, and Ti-6Al-4 V alloy is mainly used as implant material for clinical use. In particular, research on the formation of nanotubes for drug doping to improve biocompatibility is in progress. For the control of nanotube shape, in this study, nanotube shape changes on Ti-6Al-4 V alloy via various applied potential for bio-implants were researched using various instruments. The formation of nanotubes on the surface of the Ti-6Al-4 V alloy was performed using a DC power source as a two-electrode system, and platinum as a counter electrode and a working electrode as an anode. The electrolyte was 0.8 wt. % NaF solution and 1.0 M H3PO4 were used and mixed using a magnetic bar during anodization. At this time, the voltage applied when forming the nanotubes was varied as (10 → 20 → 30 V), (30 → 10 → 30 V), and (10 → 30 → 30 V), respectively, and these voltages were applied for 30 min for each step. After the formation of nanotubes, the surface morphology and structural properties of the samples were observed using field-emission scanning electron microscope, X-ray diffractometer, Fourier transform infrared spectroscopy, and nanoindentation tester. The higher the voltage applied during the formation of nanotubes, the larger is the diameter. In the case of the nanotube (10 → 20 → 30 V), the top of the nanotube was narrow and the diameter increased toward the bottom, forming a cone shape. In the case of the nanotube (30 → 10 → 30 V), a narrow waist shape was formed, and in the case of the nanotube (10 → 30 → 30 V), a jar shape was formed with anatase and rutile phases. From the FT-IR results, when nanotubes are formed, TiO2 anatase was detected and showed the tendency to change from crystallization to amorphous state. The indentation hardness and elastic modulus decreased for the nanotube surface compared with those of the bulk Ti alloy. [ABSTRACT FROM AUTHOR]

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]