Bukhari Faiza, Ansari Umar, Najabat Ali Murtaza, Akhtar Hafsah, Asif Sarim, Mohammad Umer, Mir Mariam
Biomedical Engineering and Sciences Department, School of Mechanical and Manufacturing Engineering, National University of Sciences and Technology (NUST), Islamabad - Pakistan.
J Appl Biomater Funct Mater. 2017 Jul 27;15(3):e196-e205. doi: 10.5301/jabfm.5000326.
Auxetics, a special class of materials, tend to expand both in the radial and longitudinal directions when a unidirectional tensile force is applied. Recently, studies have come up with new designs for auxetic vascular and nonvascular stents which are deployed with commercial balloon catheters. There are some inherent limitations associated with a unidirectional application of expansion force in the effective deployment of stents. This work proposed a solution to some of these limitations through the use of a biaxial mode of a predetermined strain-based expansion mechanism.
The design incorporated a pressure-activated crank-slider mechanism. Fabrication of a prototype for experimental verification was carried out through milling and high-speed lathe machining. The testing of the device employed the use of auxetic stents, fabricated from a biocompatible polymer. A finite element study is presented to extrapolate experimental results to a broader range of operation and working conditions.
The expansion mechanism is similar in operation to the opening of an umbrella. The length of the connected auxetic stent increases when internal hydraulic pressure is applied. The degree of linear expansion in 1 direction influences the expansion of auxetic stent in the lateral direction. As the device exerts pressure longitudinally, a larger amount of the force is distributed on the unit cells/hinges which ultimately results in an increased expansion of the stent.
拉胀材料是一类特殊的材料，当施加单向拉力时，它们在径向和纵向都会膨胀。最近，研究人员提出了用于拉胀血管和非血管支架的新设计，这些支架可通过商用球囊导管展开。在支架的有效展开过程中，单向施加膨胀力存在一些固有的局限性。这项工作通过使用基于预定应变的双轴膨胀机制，对其中一些局限性提出了解决方案。
该设计采用了压力激活的曲柄滑块机构。通过铣削和高速车床加工制作了用于实验验证的原型。该装置的测试使用了由生物相容性聚合物制成的拉胀支架。进行了有限元研究，以将实验结果外推到更广泛的操作和工作条件范围。
该膨胀机制的操作类似于雨伞的打开。当施加内部液压时，相连拉胀支架的长度会增加。一个方向上的线性膨胀程度会影响拉胀支架在横向的膨胀。由于该装置在纵向施加压力，更多的力分布在单元晶格/铰链上，最终导致支架的膨胀增加。
