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Local pH and Its Evolution Near Mg Alloy Surfaces Exposed to Simulated Body Fluids
Advanced Materials Interfaces ( IF 5.4 ) Pub Date : 2018-06-19 , DOI: 10.1002/admi.201800169
Sviatlana V. Lamaka 1 , Jorge Gonzalez 2 , Di Mei 1 , Frank Feyerabend 2 , Regine Willumeit-Römer 2, 3 , Mikhail L. Zheludkevich 1, 3
Affiliation  

Many reports are available on degradation rates and corrosion product characterization of magnesium alloys for implant application. Typically, the data are obtained ex situ, as post factum analysis of occurred degradation processes or in bulk electrolyte that does not fully reflect concentration gradients at the interface and in the diffusion layer. Meanwhile, these local conditions are essential for tissue‐implant compatibility. Only a limited number of studies employ the techniques that visualize ongoing degradation and are localized enough to observe the changes in the electrolyte layer directly adjacent to corroding magnesium. Here, local pH in Hank's solution is studied in operando, with potentiometric micro‐probes (d = 2 µm) located 10–50 µm above the surface of four Mg alloys potentially relevant for implant applications. A significant difference in local pH is observed for Mg in simple Hank's solution (near surface pH 9.9–10.5) or Hank's solution modified with 2.5 × 10−3 m Ca2+ (pH 7.8–8.5). The corresponding pH values are established during the first seconds of immersion. These findings indicate different degradation kinetics in electrolytes with or without Ca2+. The degradation rate of Mg alloys decreases by almost two times in Ca2+ containing Hank's solution. Calcium‐phosphate/carbonate protective layer stabilizes the surface pH below 8.5 controlling Mg degradation.

中文翻译:

暴露于模拟体液的镁合金表面附近的局部pH及其演变

关于植入物使用的镁合金的降解速率和腐蚀产物表征,已有许多报道。通常,数据是在非原位获得的,是对发生的降解过程进行的事后分析,或者是不能完全反映界面和扩散层中浓度梯度的本体电解质。同时,这些局部条件对于组织-植入物的兼容性至关重要。仅有限数量的研究采用了可视化进行中的降解并定位在足以观察到与腐蚀的镁直接相邻的电解质层中的变化的技术。在这里,对Hank溶液中的局部pH进行了操作研究,电位微探针(d = 2 µm)位于四种可能与植入物应用有关的Mg合金表面上方10–50 µm处。−3 m Ca 2+(pH 7.8–8.5)。在浸入的最初几秒钟内建立相应的pH值。这些发现表明在有或没有Ca 2+的电解质中不同的降解动力学。在含Hank溶液的Ca 2+中,Mg合金的降解速率几乎降低了两倍。磷酸钙/碳酸盐保护层可将表面pH值稳定在8.5以下,从而控制Mg的降解。
更新日期:2018-06-19
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