Pelton A R, Schroeder V, Mitchell M R, Gong Xiao-Yan, Barney M, Robertson S W
Nitinol Devices and Components, 47533 Westinghouse Dr., Fremont, CA 94539, United States.
J Mech Behav Biomed Mater. 2008 Apr;1(2):153-64. doi: 10.1016/j.jmbbm.2007.08.001. Epub 2007 Sep 20.
Nitinol self-expanding stents are effective in treating peripheral artery disease, including the superficial femoral, carotid, and renal arteries. However, fracture occurrences of up to 50% have been reported in some stents after one year. These stent fractures are likely due to in vivo cyclic displacements. As such, the cyclic fatigue and durability properties of Nitinol-based endovascular stents are discussed in terms of an engineering-based experimental testing program. In this paper, the combined effects of cardiac pulsatile fatigue and stent-vessel oversizing are evaluated for application to both stents and stent subcomponents. In particular, displacement-controlled fatigue tests were performed on stent-like specimens processed from Nitinol microtubing. Fatigue data were collected with combinations of simulated oversizing conditions and pulsatile cycles that were identified by computer modeling of the stent that mimic in vivo deformation conditions. These data are analyzed with non-linear finite element computations and are illustrated with strain-life and strain-based constant-life diagrams. The utility of this approach is demonstrated in conjunction with 10 million cycle pulsatile fatigue tests of Cordis SMART Control((R)) Nitinol self-expanding stents to calculate fatigue safety factors and thereby predict in vivo fatigue resistance. These results demonstrate the non-linear constant fatigue-life response of Nitinol stents, whereby, contrary to conventional engineering materials, the fatigue life of Nitinol is observed to increase with increasing mean strain.
镍钛诺自膨胀支架在治疗外周动脉疾病方面有效，包括股浅动脉、颈动脉和肾动脉。然而，据报道，一些支架在一年后骨折发生率高达50%。这些支架骨折可能是由于体内周期性位移所致。因此，基于工程的实验测试程序讨论了镍钛诺基血管内支架的循环疲劳和耐久性特性。本文评估了心脏搏动疲劳和支架-血管尺寸过大的综合影响，以应用于支架和支架子部件。特别是，对由镍钛诺微管加工而成的类似支架的试样进行了位移控制疲劳试验。通过模拟尺寸过大条件和脉动循环的组合收集疲劳数据，这些条件是通过对模拟体内变形条件的支架进行计算机建模确定的。这些数据用非线性有限元计算进行分析，并用应变寿命和基于应变的等寿命图进行说明。结合Cordis SMART Control((R))镍钛诺自膨胀支架的1000万次循环搏动疲劳试验，证明了该方法的实用性，以计算疲劳安全系数，从而预测体内抗疲劳能力。这些结果证明了镍钛诺支架的非线性恒定疲劳寿命响应，与传统工程材料相反，观察到镍钛诺的疲劳寿命随着平均应变的增加而增加。
