Laboratory for Biomaterials and Bioengineering, Canada Research Chair I in Biomaterials and Bioengineering for the Innovation in Surgery, Department of Min-Met-Materials Engineering, Research Center of CHU de Quebec, Division of Regenerative Medicine, Laval University, Quebec City, QC G1V 0A6, Canada; Department of Mechanical Engineering, Politecnico di Milano, Milan 20156, Italy.
Laboratory for Biomaterials and Bioengineering, Canada Research Chair I in Biomaterials and Bioengineering for the Innovation in Surgery, Department of Min-Met-Materials Engineering, Research Center of CHU de Quebec, Division of Regenerative Medicine, Laval University, Quebec City, QC G1V 0A6, Canada.
Acta Biomater. 2019 Oct 15;98:103-113. doi: 10.1016/j.actbio.2019.04.030. Epub 2019 Apr 17.
While Fe-based alloys have already been reported to possess all mechanical properties required for vascular stenting, their relatively low degradation rate in vivo still constitutes their main bottleneck. The inflammatory reaction generated by a stent is inversely proportional to its mass. Therefore, the tendency in stenting is to lower the section so to reduce the inflammatory reaction. Twinning-induced plasticity steels (TWIP) possess excellent mechanical properties for envisaging the next generation of thinner degradable cardiovascular stents. To accelerate the degradation, the addition of noble elements was proposed, aimed at promoting corrosion by galvanic coupling. In this context, silver was reported to generally increase the degradation rate. However, its impact on the deformation mechanism of TWIP steels has not been reported yet. Results show that the use of Ag significantly reduces the ductility without altering the strength of the material. Furthermore, the presence of Ag was found to promote a different deformation texture, thus stimulating the formation of mechanical martensite. Since a stent works in the deformed state, understanding the microstructure and texture resulting from plastic deformation can effectively help to forecast the degradation mechanisms taking place during implantation and the expected degradation time. Moreover, knowing the deformed microstructure allows to understand the formability of very small tubes, as precursors of the next generation of thin section degradable stents. STATEMENT OF SIGNIFICANCE: Commercial degradable magnesium stents are limited from their relatively big structure size. Twinning-induced plasticity steels possess outstanding mechanical properties, but their degradation time goes beyond the timeframe expected from clinics. The inclusion of noble Ag particles, which favor galvanic coupling, is known to promote corrosion and solve this limitation. However, it is necessary to understand the impact that Ag has on the deformation microstructure and on the mechanical properties. The addition of Ag reduces the ductility of a twinning-induced plasticity steel because of a different deformation microstructure. Since a stent works in a deformed state inside an artery, understanding the microstructural evolution after plastic deformation allows to better predict the device performances during service life.
虽然铁基合金已经被报道具有血管支架所需的所有机械性能，但它们在体内的降解速率相对较低仍然是其主要瓶颈。支架产生的炎症反应与支架的质量成反比。因此，支架的趋势是降低截面以减少炎症反应。孪生诱发塑性钢（TWIP）具有优异的机械性能，可用于设想下一代更薄的可降解心血管支架。为了加速降解，提出了添加贵金属的方法，旨在通过电偶耦合促进腐蚀。在此背景下，据报道银通常会提高降解速率。然而，其对 TWIP 钢变形机制的影响尚未见报道。结果表明，使用银会显著降低材料的延展性，而不会改变其强度。此外，发现银的存在促进了不同的变形织构，从而刺激了机械马氏体的形成。由于支架在变形状态下工作，了解塑性变形产生的微观结构和织构可以有效地帮助预测植入过程中发生的降解机制和预期的降解时间。此外，了解变形后的微观结构可以帮助理解非常小的管的成形性，因为它们是下一代薄截面可降解支架的前身。意义陈述：商业可降解镁支架由于其相对较大的结构尺寸而受到限制。孪生诱发塑性钢具有优异的机械性能，但它们的降解时间超出了临床预期的时间框架。添加有利于电偶耦合的贵金属 Ag 颗粒被认为可以促进腐蚀并解决这一限制。然而，有必要了解 Ag 对变形微观结构和力学性能的影响。Ag 的添加降低了孪生诱发塑性钢的延展性，因为其变形微观结构不同。由于支架在动脉内处于变形状态，因此了解塑性变形后的微观结构演变可以更好地预测器件在使用寿命期间的性能。
