Electrochemical Research On Corrosion Process Of Biomedical AZ31Magnesium Alloy In The Presence Of Protein

Recently, magnesium alloys, which have excellent biocompatibility and mechanicalproperties as biodegradable metallic materials, are attracting more attention, especiallytheir corrosion properties. It was found that the in vivo corrosion rate largely deviated fromthat from in vitro tests. The diviation may be caused by the difference between the in vivoand in vitro testing environments. Simulated body fluids used in the in vitro tests containthe inorganic salt composition similar to human body fluids, but human body fluids containnot only inorganic salt but also organic composition (protein, amino acid, glucose, etc.) andCO2, which is generated during metabolic process. In addition, after the implants areimplanted into human body, the pH value of body fluid nearby the implants will bechanged. However, the pH value of SBF used in in vitro tests is approximately7.4, whichmay also cause the deviation of in vivo and in vitro corrosion behaviors of magnesiumalloys. The aforementioned deviation could seriously affect the reliability of in vitro resultsas the reference data of the following clinical trials, and restrict the development ofmagnesium and its alloy as the degradable implants. So it is significant to understand the invitro corrosion mechanism of magnesium alloys under the influence of different factors,which can provide the accurate experimental data and theoretical support for the in vivotests of magnesium and its alloys.In the present work, the effect of pH value of Hank’s solution, the concentration ofbovine serum albumin (BSA), the interaction between bovine serum albumin (BSA) andfibrinogen (Fb), the existence of CO2, surface roughness on the corrosion behavior of pureMg and AZ31will be investigated, and the influencing mechanism of these factors on thecorrosion properties of magnesium alloys will also be clarified.The corrosion behavior of as-cast pure Mg and AZ31is influenced by the variation ofpH value in Hank’s solution. The corrosion current density decreases with the increase ofpH value, where the effect of pH value on corrosion rate is obvious especially when pHvalue is below6.0. The corrosion rate of pure Mg obtained in Hank’s solution (pH5.5) isabout1.6times higher than that in Hank’s solution (pH7.5),2fold for AZ31. The surfacemorphology indicates that the integrity of the corrosion product layer is improved withincreasing pH value at the same immersion time, and electrochemical impedancespectroscopy（EIS）results also shows that the surface film resistance increases withincreasing pH value.The corrosion current density of pure magnesium and AZ31magnesium alloy decreased with higher BSA concentration in Hank’s solution. The rise of pH value forHank’s solution strengthened the inhibitory effect of BSA on the corrosion of magnesiumalloy. Corrosion inhibition efficiency (ηz,) of BSA increased with its concentration.Corrosion appearance observe indicated that integrity and compaction of corrosion productlayer reinforced with the increasing BSA concentration, which could provided moreeffective protection against corrosion. Interaction between BSA and Fb provided muchhigher inhibition efficiency than BSA alone, the inhibition efficiency raised from0.1~0.2for BSA alone to0.6~0.7for BSA+Fb.The corrosion behavior of pure Mg in PBS+BSA solution saturated with CO2was alsoinvestigated in this work. It is found that the corrosion rate of pure Mg in this solution sincreases with increasing BSA concentration. Surface corrosion product layer obtained inPBS+BSA solution with CO2is more complete and compact than that in PBS+BSAsolution.The effect of surface roughness on the corrosion behavior of AZ31in Hank’s solutionwith BSA is also studied. The results show that the greater roughness leads to the highercorrosion rate. When the surface roughness is0.137μm, the corrosion current density ofAZ31is about29.2μA·cm-2. In contrast, it is about43.7μA·cm-2when the surfaceroughness rises to0.369μm. The surface corrosion morphology indicates that the additionof BSA could reduce the probability of pitting corrosion for AZ31alloy.