Laboratory of Biological Structure Mechanics, Department of Structural Engineering, Politecnico di Milano, Italy.
J Mech Behav Biomed Mater. 2011 Apr;4(3):352-65. doi: 10.1016/j.jmbbm.2010.11.003. Epub 2010 Nov 16.
The main drawback of a conventional stenting procedure is the high risk of restenosis. The idea of a stent that "disappears" after having fulfilled its mission is very intriguing and fascinating, since it can be expected that the stent mass decreases in time to allow the gradual transmission of the mechanical load to the surrounding tissues owing to controlled dissolution by corrosion. Magnesium and its alloys are appealing materials for designing biodegradable stents. The objective of this work is to develop, in a finite element framework, a model of magnesium degradation that is able to predict the corrosion rate, thus providing a valuable tool for the design of bioresorbable stents. Continuum damage mechanics is suitable for modeling several damage mechanisms, including different types of corrosion. In this study, the damage is assumed to be the superposition of stress corrosion and uniform microgalvanic corrosion processes. The former describes the stress-mediated localization of the corrosion attack through a stress-dependent evolution law, while the latter affects the free surface of the material exposed to an aggressive environment. Comparisons with experimental tests show that the developed model can reproduce the behavior of different magnesium alloys subjected to static corrosion tests. The study shows that parameter identification for a correct calibration of the model response on the results of uniform and stress corrosion experimental tests is reachable. Moreover, three-dimensional stenting procedures accounting for interaction with the arterial vessel are simulated, and it is shown how the proposed modeling approach gives the possibility of accounting for the combined effects of an aggressive environment and mechanical loading.
传统支架置入术的主要缺点是再狭窄的风险高。支架在完成使命后“消失”的想法非常有趣和吸引人，因为可以预期支架的质量会随着时间的推移而减少，从而允许机械负荷逐渐传递到周围组织，这是由于腐蚀的控制溶解。镁及其合金是设计可生物降解支架的有吸引力的材料。这项工作的目的是在有限元框架内开发一种能够预测腐蚀速率的镁降解模型，从而为生物可吸收支架的设计提供有价值的工具。连续损伤力学适用于模拟多种损伤机制，包括不同类型的腐蚀。在这项研究中，损伤被假设为应力腐蚀和均匀微电偶腐蚀过程的叠加。前者通过依赖于应力的演化律描述了腐蚀攻击的应力介导局部化，而后者则影响暴露于腐蚀性环境的材料的自由表面。与实验测试的比较表明，所开发的模型可以再现不同镁合金在静态腐蚀测试下的行为。该研究表明，对于模型响应的正确校准，参数识别可以通过均匀和应力腐蚀实验测试的结果来实现。此外，还模拟了考虑与动脉血管相互作用的三维支架置入术，并展示了所提出的建模方法如何能够考虑到腐蚀性环境和机械加载的综合影响。
