Electrochemical corrosion behaviour of hydroxyapatite-glass-titanium composite

To determine whether hydroxyapatite(HA)-containing glass would exhibit the desired stability and activity under in vivo conditions, electrochemical corrosion behaviour of HA-glass-titanium composites was estimated by anodic polarization measurement in a simulated body fluid, 0.001 N HCl solution, 0.1 M NaCl solution, 0.1% albumin solution, and 0.1% fibrinogen solution. Potentiostatic anodic polarization measurements were made from each rest potential to +2 V versus s.c.e. with an increasing rate of 1 mV/s. Anodic polarization curves for pure titanium provided typical passive corrosion behaviour in HCl solution. The breakdown potentials were +1.4 V in HCl solution and +1.2 V in other solutions. The glass-coated specimens showed extremely low current density, less than 0.001 microA/cm2, from rest potential to about +1.8 V, and showed a slight increase in current density over +1.8 V. The polarization curves for the HA-glass-Ti composites were quite different from those for Ti and the glass-coated specimens. The current density for 50-90% HA -glass-Ti composites increased drastically from less than 0.001 to 10 microA/cm2 around rest potential (about -0.5 V), and continued to rise slightly up to +2 V. Addition of protein in NaCl solution exhibited little effect on anodic polarization curves for Ti and HA-glass-Ti composites.