A bioactive Ti metal with a Ca-enriched surface layer releases Mg ions

Abstract

A bioactive surface layer that released Mg²⁺ ions was produced on the surface of titanium metal (Ti) by chemical and heat treatments. Ti was soaked in 5 M NaOH solution at 60 °C for 24 h to form sodium hydrogen titanate (SHT) on its surface. Then, it was soaked in a mixed solution of 100−X mM CaCl₂ and X mM MgCl₂ (X represents a range from 20 to 80) at 40 °C for 24 h to replace Na⁺ ions in the SHT with Ca²⁺ and Mg²⁺ ions in a range of 0.10 to 0.93 in Mg/Ca ratio. When the metal with a 0.43 in Mg/Ca ratio on its surface was heat-treated at 600 °C for 1 h, magnesium-containing calcium titanate (MCT), anatase and rutile formed on the Ti surface. When the metal formed with MCT was subsequently soaked in water or 1 M MgCl₂ solution at 80 °C for 24 h, the Ca²⁺ and Mg²⁺ ions in MCT were partially replaced with H₃O⁺ ions. Thus, the treated metal released 0.02 or 0.43 ppm of Mg²⁺ ions within 7 days in 2 ml of phosphate buffered saline and formed bone-like apatite on its surface within 1 day in a simulated body fluid. The Ti formed with this kind of bioactive MCT layer on its surface is expected to be useful for orthopedic and dental implants, since it should be able to promote bone growth by releasing Mg²⁺ ions and tightly bond to the bone through the apatite formed on its surface.