低频动载作用下镁合金与涂层的降解行为及其频率特性

During the service process in vivo, the orthopedics fixation and cardiovascular stents made of biodegradable magnesium alloys will be affected by the dynamic loads with low frequencies caused by physiological activities, which will have an impact on the degradation behavior and service life of magnesium based implant. This project is to study the degradation behavior and its frequency characteristics of magnesium alloys and their surface coatings under the dynamic loads with normal physiological frequencies (0.5~3Hz) in the physiological environment. Using the static/dynamic electrochemical analysis platform, the electrochemical behavior and its frequency characteristics of magnesium alloys and their coatings will be monitored in real time. A three dimensional dynamic impedance profile is established. The relationship between the local damage of the coating and the degradation behavior of the magnesium alloy was investigated by means of studying the impedance changes and the degradation behavior around the coating failure zone, which provides a theoretical basis for the introduction of local damage model in the simulation degradation process and the structural design of magnesium based implants. The dynamic mechanism and its frequency characteristics of different coating materials on the degradation behavior of magnesium alloys under the dynamic loads with low frequencies will be studied, which will provide a theoretical guidance for the design of surface coatings on magnesium based implants. In addition, through the implementation of this project, it can also provide a scientific method to study the degradation behavior of poly-lactic acid, zinc based alloys and other degradable orthopedics and stent materials under the dynamic loads with low frequencies.

可降解镁合金骨科固定器和心血管支架在体内服役过程中受到生理活动引起的低频动态载荷作用，进而影响其降解行为和服役寿命。本项目拟开展在具有人体正常生理频率（0.5~3 Hz）的低频动载作用下镁合金及其表面涂层在生理环境中的降解行为及其频率特性研究。采用静/动态微区电化学分析实验平台，实时监测镁合金及其涂层的微区电化学行为变化及其频率特性，建立随时间变化的三维动态阻抗分布图。研究涂层破坏区域周围的阻抗变化以及降解行为，建立涂层局部破坏与镁合金整体降解行为之间的关系，为镁合金植入器件的结构设计和降解模拟过程中引入微区局部破坏模型提供理论依据。揭示低频动载作用下不同涂层材料对镁合金基体降解行为的动态影响机制及其频率特性，为镁合金器件的涂层设计提供理论指导。通过本项目实施，还可为研究低频动载作用下聚乳酸、锌基合金等其它可降解骨科固定器和血管支架材料的降解行为提供科学的试验方法。

项目期内，首先研制了符合项目研究要求的可实现施加模拟生理静态载荷、弯曲载荷、低频动态拉压交替循环载荷等模拟生理应力环境并能实时监测镁合金及其涂层表面微区电化学行为的静/动态微区电化学分析实验平台。基于该实验平台，分别系统研究了在静态载荷、低频动载作用下镁合金及其表面涂层的局部腐蚀机制、降解行为及其频率特性，对比分析了静态应力和动态应力对镁合金及其表面涂层降解行为的不同影响规律。.研究发现，静态应力环境会加速镁合金的腐蚀，应力值越大，镁合金的腐蚀速率越快，但随时间延长逐渐降低并趋于稳定。WE43镁合金在腐蚀前期受静态应力影响更大，AZ31镁合金则在腐蚀后期对静态应力值更敏感。载荷形式上，静态拉伸载荷比压缩载荷对镁合金腐蚀的加速作用更明显。不同镁合金的腐蚀速率vcorr和静态应力值σ之间存在 ln vcorr∝ σ的线性关系。.低频动载对镁合金及其表面涂层腐蚀降解的加速效果比静态应力更明显，动载频率越大，镁合金及其表面涂层腐蚀速率越快。低频动载对镁合金表面腐蚀产物和钙磷相的沉积有一定的促进作用，但不影响动态应力对镁合金腐蚀的加速效果。系统研究了不同低频动载作用下不同镁合金与涂层的降解行为，揭示了动态载荷频率对镁合金表面涂层使役寿命的影响规律，分析讨论了动态拉压交变循环载荷下镁合金及其表面涂层的局部腐蚀破坏机制。基于实时监测获得的镁合金及其涂层表面微区电化学行为变化规律及其频率特性，构建了动载载荷频率与镁合金腐蚀速率的数值关系。在低频动态应力作用下，镁合金腐蚀早期的vcorr与频率f之间存在ln vcorr∝ f的线性定量关系，电化学和失重实验结果表明该定量线性关系吻合程度良好，在给定实验条件下具有一定的普适性。.本项目研究成果可为体内应力服役生理环境中可降解骨科固定器和血管支架材料的降解行为和使役寿命预测提供科学的体外评价方法，具有重要的理论意义和参考价值。