Preparation And Mechanical Performance Of New Integrated Braided Stent Grafts

With the improvements in living standards and dramatic ageing of the population, the incidence of peripheral vascular diseases is increasing year by year. Angiostenosis diseases are serious threats to human health. Stent implantation, as a minimally invasive surgery, is an effective therapy for vascular stenosis and is widely used in clinical. But in-stent restenosis often occurred after the implantation, which is usually related to the mechanical properties of the stent. So researches on design and manufacture of stent with new structures are of significant value. Due to the wide range and differentiation in stents, there is no uniform standard for mechanical evaluations of the stents. The characterizations of newly designed stents also need to be further studied.Textile technology was used in this study to produce new stents with excellent mechanical properties, which can be employed to reduce the incidence of in-stent restenosis. The polyester yarns and nitinol wires were braided together to form a tubular structure, acting as the new integrated stent grafts. The high flexibility of the braided structure provides the stents with good longitudinal pliability, easy fitting ability to the host blood vessels, and less neointimal hyperplasia. In addition, the existence of polyester yarns could effectively reduce the relative slipping among nitinol wires, providing a better radial strength.This paper includes two main parts: one is the design and preparation; another is mechanical performance evaluations of the new integrated braided stents. In the design and preparation part, the feasibility of using two dissimilar materials(polyester yarns and nitinol wires) to braid stents was explored. The preparation method was set as nitinol wires heat setting followed by braiding. On this basis, the optimum time and temperature parameters of heat-setting procedure were investigated in order to maintain the superelasticity and spiral shape for further braiding process. By varying the number and distribution of nitinol wires, four kinds of different integrated stents were prepared.In terms of the mechanical evaluations, several in vitro methods were used to measure the mechanical properties of four new integrated vascular stents, including contractility, radial support performance, and bending and torsion performances. Axial tensile tests showed that four stents had good contractility and elastic resilience. In planar compression test, the stent graft(A2), which had parallel spiral nitinol wires and short pitch length, exhibited the best compression performance among the four stents. It gave a relative higher compression force, lower stress relaxation ratio and higher elastic recovery rate. In bending and torsion performances test, all the four integrated braided stents showed a lower counter-acting force compared to the bare metal stent. This is helpful to keep the blood flowing smoothly and will reduce vascular trauma in clinical application.After comprehensive study of the preparation and characterization of new integrated braided stents, the preparation method taking advantages of braiding technique was proved to be feasible. The rationalization of integrated braided structures was further verified through mechanical performance evaluations. This study established the foundation for further improvement in preparation and in vivo trails of the new integrated braided stent.