Effect of pH on the in vitro corrosion rate of magnesium degradable implant material

Magnesium (Mg) has been recently advocated as a potential metallic material for degradable bone plates. The corrosion behavior of Mg in body fluids at different pH values, however, has not been fully studied. The pH value of the body fluid at the location of bone fracture changes during the course of recovery, and study of the effect of pH on the corrosion rate of Mg provides important information in the development and design of Mg implants. In the present study, the corrosion behavior of Mg in Hanks' solution (a simulated body fluid) at pH value ranging from 5.5 to 8.0 was studied via monitoring the rate of hydrogen gas evolution. The experimental results show that the pH value has very large effect on the corrosion rate in Hanks' solution within the range 5.5 to 8.0. The corrosion rate (penetration rate) at pH 5.5 exceeds 800 μm per day, which is extremely high. On the other hand, it drops to about 6 μm and 3 μm per day at pH 7.4 and 8.0, respectively. The corrosion behavior of Mg at different pH values was also studied using electrochemical methods, including potentiodynamic polarization measurement and electrochemical impedance spectroscopy (EIS).