Structural Optimization Design Of Medical NiTi Stent

NiTi alloy provides superelasticity. We can use this property to make self-expanded stent, which takes on excellent biocompatibility and mechanical properties. Three-dimensional (3D) finite element emulational models of differently designed NiTi stents were constructed by a 3D software Pro/Engineering and a finite element analysis (FEA) software Ansys8.1. The compression resistance property, flexibility, implantation property and stress distribution of the NiTi stent were calculated, and correlative experimental validations were done to investigate the influence of different factors.The results show that the stress is generally focused on the corner of NiTi stent's struts when the stent is deformed, so it is important to increase the width and the thickness of the struts, or decrease the angle of the corner of the struts. It is one of the most important matters of the collapse of the stent that martensite transition caused by stress in the process of the compression resistance property and flexibility. If the structural element of the stent is symmetrical, the uniform stress appears by force, furthermore, the stress concentration is avoided effectively, and the maximum stress decreases obviously. The stent's radial strength is improved equivalently with the increasing of the strut's width or thickness, and the stent's flexibility is improved with the increasing of the strut's width or thickness, but the influence of the width is larger than that of the thickness. The structure of supporting frame and short struts is more flexible than that of only supporting frame. The sinusoid-like element structure is provided with high compression proportion, and can be put into the little transporter. The distortion and stress distribution is symmetrical after dilatation. It improve the anti-fatigue property, and is provided with high supporting strength. Generally, after the stent releases, it will cause the end of blood vessel high stress, which is easy to damage the blood vessel, and arouse the thrombus, film hyperplasia and so on.In the paper, the results that influences on the NiTi stent's properties is systematically analyzed by the 3D FEA, which supplies the designing theories to the optimization design of the NiTi stents. According to the results of FEA and clinical data, a new structural NiTi stent is designed. The stent is composed of the sinusoid-like element supporting frame and short struts.The mechanical properties of the new stent are all right, and the stress distribution is symmetrical. The aim of optimization design is achieved.