Dissolution and Repassivation Behaviour of Ti, Ti-6Al-4V, Type316L and Co-27Cr-5.5Mo in Bio-Mechano-Chemical Environment

Dissolution and Repassivation during and after passivity breakdown of four kinds of metallic biomaterials in simulated body fluid were examined using rapid straining electrode test. The materials were pure titanium, Ti-6Al-4V alloy, type 316L stainless steel and Co-Cr alloy. Rapid straining was applied for electrodes of these materials that were immersed in a simulated body fluid containing proteins for 1 day, 1 week or 1 week with cell culturing prior to the test, then changes in strain, stress and anodic current were observed simultaneously.

The maximum anodic current density during rapid straining was observed for pure titanium. However, maximum charge density generated after rapid straining until 100 s from the termination of rapid elongation was observed for type 316L stainless steel. These results suggest that the amount of dissolution of metallic biomaterials with passivity breakdown depends on the equilibrium potential of metal substrates and repassivation rate.

The charge densities generated on the samples immersed for 1 week in the simulated body fluid prior to the rapid elongation and covered with cells was larger than that generated on the sample immersed for 1 day in pure Ti, Ti-6Al-4V alloy and type 316L stainless steel. The highest increase rate of the charge density was confirmed in the sample covered with cells of type 316L stainless steel.