AbstractsEngineering

M.S. University of Hawaii at Manoa 2012. Stents are small, wire-mesh struts that are placed into arteries after an angioplasty procedure. The purpose of a stent is to help keep the portion of the blood vessel that has been treated with angioplasty open after the procedure. Stents have been used to help substantially reduce the restenosis associated with angioplasty procedures. Two broad categories of stents are self-expanding and balloon expanding. Balloon expandable stents have been available for several years, but the application of shape memory alloys to the manufacture of stents is relatively new. The differences between the two stents stem mainly from the material of construction. Self-expanding stents are investigated in this study. In particular, the mechanical response of a bare stent made of a shape memory alloy (SMA), Nitinol is investigated here. The Nitinol stent is investigated experimentally and using finite element methodology (FEM). The Guidant Absolute Nitinol Stent is experimentally tested for various uniaxial tensile loading conditions. In addition the stent specimen was subject to compressive, and crush loads as well. The stent geometry was rendered using computer aided design (CAD) software, Solidworks. Several different lengths of the stent were created, but only 7.30, 10.87, 14.42 mm stents were subject to the same uniaxial tensile, and compression loads. The crush test was not simulated. In addition three modifications to the Absolute stent geometry were also created and tested for the same uniaxial tensile loads. Results from the simulation were validated against the experimentally acquired results. Comparison of the simulation and experimental results reveals that the load-strain relationship from the different simulated lengths is similar to that found experimentally. The simulation represented the elastic region of the Nitinol stent under tensile loading well. The experimental results showed a steeper elastic region, which was accounted for by the increased length of the stent. The load-strain curve comparison reveals that the load at which the Nitinol undergoes phase transformation is 0.9 N from experiment and approximately 0.7 N from the simulations. The model correctly predicted the locations of concentrated stress, in turn, accurately identifying the regions that would be expected to suffer structural failure. Moreover, the geometry modifications reveal a dependence of the stiffness of the stent on the number, location, and length of the bridge elements.