Formation of calcium phosphates on low-modulus Ti–7.5Mo alloy by acid and alkali treatments

This study investigated the hydroxyapatite (HA) coating on metal implants in order to enhance their bioactive properties. In this study, HA coatings were formed on the surfaces of commercially pure titanium (c.p. Ti) and Ti–7.5Mo which were acid-etched and subsequently alkali-treated before samples were soaked in simulated body fluid (SBF). Specimens of c.p. Ti and Ti–7.5Mo were etched in either H₃PO₄ or HCl, and subsequently treated in NaOH. The surfaces of acid-etched c.p. Ti showed a porous structure, whereas those of acid-etched Ti–7.5Mo showed some grinding marks, but no porosity. After subsequent alkali treatment in NaOH, the surfaces of both the c.p. Ti and Ti–7.5Mo substrates exhibited microporous network structures. The specimens were then immersed in SBF at 37 °C for 28 days. Apatite began to deposit on acid-etched and NaOH-treated Ti–7.5Mo within 1 day after immersion in the SBF. After 28 days of immersion in the SBF, a dense and uniform layer was produced on the surfaces of all samples. The HA formation rate was the highest for HCl and NaOH-pretreated samples, and the results of EDS and XRD showed that much more intensive peaks of HA appear on the specimens of HCl and NaOH-treated Ti–7.5Mo than on any other sample. Thus, this method of apatite coating Ti–7.5Mo appears to be promising for artificial bone substitutes or other hard tissue replacement materials with heavy load-bearing applications due to their desirable combination of bioactivity, low elastic modulus, and low processing costs.