چكيده به لاتين
In recent years, the use of arterial stents to treat coronary artery disease such as atherosclerosis has increased. Various stents with different geometries and materials have been introduced to the market. To choose the best stent geometry from the available models in the market, their performance should be carefully analyzed and the mechanical behavior of different models should be compared. This requires in vitro, in vivo and clinical trials, which save a lot of time, money and equipment. In this study, the effect of design, material and thickness of stent struts on expandability, which is one of the important properties in the selection of cardiovascular metallic stents, is investigated. Stresses on the stent bases and vessel wall, equivalent plastic strain, recoil, dog-boning effect and the coverage area by the stent are also examined. The finite element method was used to examine all behaviors and changes in the stent to evaluate the product before production and in vitro, in vivo and clinical tests. For this purpose, four commercial stents were used, i.e., Palmaz-Schatz, NIR, Biomatrix, Cypher. In addition, five more stents were proposed based on different designs and materials. The proposed stents were categorize based on thickness and material. The proposed stent in subcategory B was thinner than the those in A. The stents were divided into open cell, closed cell and hybrid designs, all of which were hybrid. The analyzes were performed using three applied materials: carbon stainless steel 316L, cobalt-chromium L605 alloy and platinum-chromium alloy, which are quite commonly used in stents. The mentioned stents were modeled in SolidWorks software and their performance was analyzed in ABAQUS software. In order to make the simulation conditions as close as possible to reality, components such as balloons and blocked vessels were also considered, which also applied moderate blood pressure to the blocked vessel. The results showed that the highest stress in stents was in the connection of the bridges with the stent struts and in the bends of the struts and bridges. Most of the plastic changes took place at the connection of the stent bridges and bends, which are actually the places where highest stresses occur. The highest stress distribution in the arteries was at the point of contact of the stent struts with the plaque and also the highest stress was applied to the intima layer. The pattern of stress distribution in the vessel at the end of the loading stage is different and most of the stresses occurred at both ends of the stent in contact with the vessel. This was due to the increased effect of the dog-boning at this stage. Open cell stents had the highest stress on the vessel, most expansion, least recoil, and the greatest dog-boning effect compared to closed and hybrid cell stents. The values of hybrid stents in the studied parameters were between open cell and closed cell stents. Stainless steel stent has the lowest stress in the stent at the end of the loading and unloading stage, the highest stress applied to the vessel at the end of the loading stage, the lowest stress applied to the vessel at the end of the loading stage, the highest plastic deformation, the most expansion and the highest recoil compared to cobalt-chromium and platinum-chromium stents. The material had a limited effect on the dog-boning effect. Indeed, the dog-boning effects of stainless steel, cobalt-chromium and platinum-chromium stents were almost equal. Changing the thickness of the stent bases had little effect on changing the stress distribution and plastic strain. Decreasing the thickness of the stent bases reduced the stress on the vessel, increased maximal expansion and recoil, and decreased the dog-boning effect. The lowest level of coverage was related to Pamaz-Schottz stent and the recently proposed stent with the lowest applied stress onto the vessel. The results showed that the proposed cobalt-chromium B stent and the proposed platinum-chromium B stent were not the weakest stents in any of the parameters compared to the studied stents, but were among the best stents in the maximum expansion parameter. Examining the three materials of stainless steel, cobalt-chromium and platinum-chromium in the proposed stents A and B, it was observed that cobalt-chromium and platinum-chromium were superior to stainless steel. Also, hybrid design can be superior to open and closed cell design when it has thinner bases, and this is achieved by using alloys such as cobalt-chromium and platinum-chromium.
