Corrosion Behavior And Mechanical Property Of Pure Zn In Simulated Body Fluids

Zinc(Zn)and its alloys have become a new generation of biodegradable vascular scaffolds due to their good biocompatibility and biodegradability.However,due to lacking of strict testing standards,consensus on the degradation mechanism of Zn and its alloys has not been reached.Physiological environment plays an important role in the corrosion of metals.When tested in vitro,differences of inorganic salts and organic components(such as proteins)in simulated body fluids could alter the corrosion behavior of stent materials.Therefore,this work focused on the influences of solution compositions on the corrosion behavior of pure Zn.Electrochemical measurements and immersion tests were utilized to evaluate the pure Zn corrosion in different solutions.(1)The effects of Cl-?HCO3-?HPO42-?SO42-and proteins(bovine serum albumin)in simulated body fluids on the corrosion of pure Zn were studied.Results showed that anion leads to the corrosion of pure Zn to some extent,and inorganic salt formed on the surface as corrosion products.However,protein can significantly reduce the corrosion of pure Zn.(2)The effect of protein concentrations on the corrosion behavior of pure Zn was studied.In the phosphate buffered saline,protein with 0.5 g L-1 firstly slowed down the corrosion of pure Zn and then accelerated it.Protein with 2 g L-1 significantly reduced deposition of phosphates on the surface and accelerated the corrosion at the initial stage of immersion.(3)The corrosion behavior of pure Zn in simulated plasma containing 60 g L-1 protein was studied.The results showed that the corrosion behavior of pure Zn was different from the results reported previously.In the simulated plasma,pure Zn encountered uniform corrosion,and the corrosion product was a complex of protein and ZnO/Zn(OH)2.The corrosion rate of pure Zn after 28 d immersion was about 16.52±0.21?m y-1,which is close to the standard of vascular scaffold materials.(4)The effect of corrosion on mechanical properties was studied.In the simulated body fluid,serious localized corrosion was observed on the pure Zn surface.And the yield strength and ultimate tensile strength were decreased from 59.31±1.33 MPa,89.93±0.62 MPa to 46.35±2.21 MPa,79.11±1.01 MPa,the elongation was reduced greatly from 81.33±3.51%to 47.04±4.09%.In the simulated plasma,the presence of proteins alleviated the localized corrosion of pure Zn.The mechanical parameters decreased slowly with the immersion time to 49.63±5.01 MPa?85.69±0.78 MPa?57.17±2.75%.After 6 months,the elongation of pure Zn was still higher than the requirement of scaffold materials.In the in vitro test,pure Zn showed different corrosion behavior in different simulated body fluids.Protein causes uniform corrosion of pure Zn and reduces the corrosion rate as well as the deposition of corrosion products.The mechanical behavior was also related to the corrosion in different solutions.Therefore,it is suggested that the influence of proteins on the corrosion behavior of pure Zn should be considered in the in vitro test,so as to make a reasonable prediction on the corrosion behavior and mechanical behavior of materials in vivo.