The long-term shape-recovery behavior of shape memory polymers has often been shown to be dependent on the length of time the material has been stored in the secondary shape. Typically, recovery performance and shape fixity will decrease with increased time in the secondary shape. In medical materials, a shelf-life is crucial to establish as it sets the upper threshold for device performance in a clinical setting, and a reduction in shape recovery would limit the development of SMP medical devices. Here, we present a two-year study of strain recovery, strain fixity, and shape recovery kinetics for passively and actively actuated SMPs intended for vascular devices. While kinetic experiments using immersion DMA indicate slight material relaxation and a decrease in the time to recovery, these changes are not found for bulk recovery experiments. The results indicate that a two-year shelf-life for these SMPs is very reasonable, as there is no change in the recovery kinetics, strain recovery, or strain fixity associated with this aging time. Further, a thermal accelerated aging test is presented for more rapid testing of the shape memory behavior of these SMPs and is compared with the real time aging results, indicating that this test is a reasonable indicator of the two-year behavior.

中文翻译：

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用于血管医疗器械的多孔热固性形状记忆聚氨酯的两年性能研究

形状记忆聚合物的长期形状恢复行为经常被证明取决于材料以二次形状储存的时间长度。通常，恢复性能和形状固定性会随着二次形状中时间的增加而降低。在医疗材料中，保质期至关重要，因为它为临床环境中的设备性能设定了上限，而形状恢复的减少将限制 SMP 医疗设备的发展。在这里，我们对用于血管装置的被动和主动驱动的 SMP 进行了为期两年的应变恢复、应变固定和形状恢复动力学研究。虽然使用浸入式 DMA 的动力学实验表明材料轻微松弛和恢复时间减少，但在整体恢复实验中没有发现这些变化。结果表明，这些 SMP 的两年保质期是非常合理的，因为与此老化时间相关的恢复动力学、应变恢复或应变固定没有变化。此外，为了更快速地测试这些 SMP 的形状记忆行为，提出了热加速老化测试，并与实时老化结果进行了比较，表明该测试是两年行为的合理指标。