Kapnisis Konstantinos, Constantinides Georgios, Georgiou Harry, Cristea Daniel, Gabor Camelia, Munteanu Daniel, Brott Brigitta, Anderson Peter, Lemons Jack, Anayiotos Andreas
Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol 3036, Cyprus.
Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol 3036, Cyprus.
J Mech Behav Biomed Mater. 2014 Dec;40:240-251. doi: 10.1016/j.jmbbm.2014.09.010. Epub 2014 Sep 16.
In-stent restenosis (ISR) remains a significant limitation despite the considerable previous clinical and investigative emphasis on the problem. Complications arising from the interaction of stent materials with the surrounding vessel wall as well as from the mechanical forces developing after implantation, play an important role in the development of ISR. To investigate the relation between mechanical factors and stent structural integrity, and to identify any structural weakness points on the geometry of commercially available Stainless Steel and Cobalt-Chromium stents, accelerated pulsatile durability tests were carried out in a simulated physiological environment. Potential spatial variations in the mechanical properties on stent struts and their role in the observed premature failures of the stent devices during operation were also examined. Fretting wear and fatigue-induced fractures were found on stent surfaces after exposure to cyclic loading similar to that arising in vivo. Nanoindentation studies performed on various locations along the stent struts have shown that the hardness of specific stent locations significantly increases after mechanical expansion. The increase in hardness was associated with a reduction of the material's ability to dissipate energy in plastic deformations, therefore an increased vulnerability to fracture and fatigue. We conclude that the locations of fatigue fractures in stent struts are controlled not only by the geometrically-driven stress concentrations developing during cyclic loading but also by the local material mechanical changes that are imparted on various parts of the stent during the deployment process.
尽管此前临床上和研究中对支架内再狭窄（ISR）问题给予了相当大的关注，但它仍然是一个重大的限制因素。支架材料与周围血管壁相互作用以及植入后产生的机械力所引发的并发症，在支架内再狭窄的发生发展中起着重要作用。为了研究机械因素与支架结构完整性之间的关系，并确定市售不锈钢和钴铬合金支架几何形状上的任何结构薄弱点，在模拟生理环境中进行了加速脉动耐久性测试。还研究了支架支柱机械性能的潜在空间变化及其在手术过程中观察到的支架装置过早失效中的作用。在暴露于类似于体内产生的循环载荷后，在支架表面发现了微动磨损和疲劳诱导的断裂。对沿支架支柱不同位置进行的纳米压痕研究表明，在机械扩张后，特定支架位置的硬度显著增加。硬度的增加与材料在塑性变形中耗散能量的能力降低有关，因此增加了骨折和疲劳的易感性。我们得出结论，支架支柱中疲劳骨折的位置不仅受循环加载过程中几何驱动的应力集中控制，还受展开过程中支架各部分局部材料机械变化的影响。
