Enhancement of corrosion resistance of titanium-copper based metallic glass by methylsiloxane coating

Bulk metallic glass composed of Ti₄₀Zr₁₀Cu ₃₆Pd₁₄ (Ti-Cu BMG) has superior mechanical properties compared to titanium metal, which makes it promising for new orthopedic implant applications. We studied improvement of the surface properties of Ti-Cu BMG, focusing on enhancing corrosion resistance and adding bioactivity with a methylsiloxane (MS) coating. The MS was prepared by hydrolysis polymerization of methyltriethoxysilane, and was coated onto Ti-Cu BMG by dipping and drying at 80 °C. The ability of the MS coating to reduce Cu ion elution from the Ti-Cu BMG was investigated by autoclaving coated disks at 121 °C for one hour in a hydrochloric acid solution controlled at pH 0.4 to 4. Cu ion elution from MS-coated Ti-Cu BMG was very low (less than 1000 ppb); this value was less than half that from uncoated Ti-Cu BMG. The MS coating retained sufficient adhesion to the Ti-Cu BMG even after the autoclave tests. The mechanism of Cu ion elution through the MS coating film appeared to be via steady-state diffusion, and the degree of reduction in ion elution was dependent on the coating thickness. Bioactivity was added by coating the Ti-Cu BMG with a calcium-containing methylsiloxane (MS-Ca) layer. The coating formed a double-layered structure of bone-like apatite after soaking in a simulated body fluid for 3 days. A series of tests indicated that MS-Ca and MS coatings were useful for improving corrosion resistance and for adding bioactivity. MS coated Ti-Cu BMG is therefore a promising material for biomedical applications.