Surface modification of a Ti–7.5Mo alloy using NaOH treatment and Bioglass® coating

The objective of this study was to propose a surface modification for a low-modulus Ti–7.5Mo alloy to initiate the formation of hydroxyapatite (HA) during in vitro bioactivity tests in simulated body fluid (SBF). Specimens of commercially pure titanium (c.p. Ti) and Ti–7.5Mo were initially immersed in a 15 M NaOH solution at 60°C for 24 h, resulting in the formation of a porous network structure composed of sodium titanate (Na2Ti5O11). Afterwards, bioactive Bioglass® particles were deposited on the surface of NaOH-treated c.p. Ti and Ti–7.5Mo. The specimens were then immersed in SBF at 37°C for 1, 7 and 28 days, respectively. The apatite-forming ability of the NaOH-treated and Bioglass®-coated Ti–7.5Mo was higher than that of the c.p. Ti under the same condition. The X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) results indicated that the deposited amounts of calcium phosphate were much greater for the surface-treated Ti–7.5Mo than for the c.p. Ti, a finding attributable to or correlated with the higher pH value of the SBF containing surface-treated Ti–7.5Mo. Moreover, in the surface-treated Ti–7.5Mo, the pH value of the SBF approached a peak of 7.66 on the first day. A combination of NaOH treatment and subsequent Bioglass® coating was successfully used to initiate in vitro HA formation in the surface of the Ti–7.5Mo alloy.