Papers by Keyword: Coronary Stent

Abstract: This article shows two examination methods to measure the metal to artery ratio of stents. Our goal was to further develop the previously used measuring method in order to make it suitable for the integration into the quality control process of endovascular stent manufacture to provide more realistic data. The previous method was performed manually using rotating equipment under a stereomicroscope. The new method is an automatic method using an integrated scanner and a rotating engine. Both methods aimed at converting the cylindrical stent into a flattened two-dimensional image in order to enable the measurement of stent surface area by imaging software. From the image we can determine the cell sizes, the maximum achievable stent diameter, and the structure of the stent pattern. Each measurement process was tested on different types of stents. Our findings showed that the methods gave similar results, the largest differences are speed and accuracy.

Abstract: Restenosis is a re-narrowing or blockage of an artery at the same site where treatment like stent procedure has already taken place. The aim of this study is to more conclusively identify the mechanical stimulus for in-stent restenosis by means of numerical model based on the finite element method. The finite element model simulating the stent, balloon, crimping tool and artery interaction in the coronary artery is developed. The present model is used to determine the stress distribution in the artery wall followed by stent implantation. It is indicated that the compliance mismatch of stent with vascular induces the stress concentration in the stented artery, which impact the level of vascular injury caused to the artery by the stent. This study supports the hypothesis that the artery develops restenosis in response to injury, where high vessel stresses are a good measure of the injury.

Abstract: Stent implantation is a non-surgical method to treat the coronary artery disease that can support vessel walls and reduce the risk of heart attack. In this paper, undertaking the 316L stainless steel as a medical stent material, a certain coronary stent is utilized to study its mechanical characteristics by the finite element analysis as it is deployed and implanted in a vessel containing a plaque, and try to reach to a model close to a real condition of stent implantation. The result shows that the width size of stent rods is greater than its thickness size in the capability of resisting deformation of configuration, and then displacement changes of the coronary stent on the axial direction should be keeping a close eye in their expansion process.

Abstract: This study proposes a novel manufacturing method, a hollow braiding technique, to make reticular tubes. Coronary stents for coronary arteries have to have a size equal to the size of the arteries, and as a result, material and diameter of stents are both critical designed parameters. By using a hollow braiding technique and a braiding machine, 316L stainless steel fibers are made into coronary stents with an internal diameter of 3 mm, which meets the requirement of coronary arteries. The experiment results show that the hollow braiding technique can effectively braid reticular tubes with an internal diameter of 3 mm. In addition, variation in tooth number on the take-up gear can influence the braiding angle but does not influence the stability of the braiding structure and metal cover rate. In this study, the hollow braiding technique successfully produces coronary stents in the form of reticular tubes with a size equal to coronary arteries.

Abstract: With the appearance of reticular tubes, coronary stents can resist the compressive strength caused by vascular pulsation. This study braids stainless steel fibers with diameters of 0.12 mm and 0.08 mm with a braiding technique, and the resulting braids are then combined with polyvinyl alcohol (PVA) solution to form three stent types-S12, PVA/S12, and PVA/S8. S12 is braids that are made of 0.12-mm-diameter stainless steel fibers, PVA/S12 is S12 coated with PVA. PVA/S8 is braids made with 0.08-mm-diameter stainless steel fibers and then coated with PVA. Surface, braiding angle, and compression behavior of the coronary stents are observed by a stereomicroscope, analyzed by Motic Images Plus 2.0 software, and examined by an Instron 5566, respectively. The experiment results show that compared to S12 and PVA/S8, PVA/S12 has a smaller braiding angle, indicating its manufacturing process is not stable. Of the three coronary stents, PVA/S8 possesses the greatest recovery from the compression, and thus this study yields optimal coronary stents with satisfactory surface, braiding angle, and recovery ability.

Abstract: Stents have been routinely used for the treatment of coronary artery occlusion since the last two decades. They are made of corrosion resistant alloys such as stainless steel 316L, titanium and cobalt-chromium alloys; in addition, their manufacturing process is well developed. Currently, corrodible metals have been proposed for making stents that can degrade after serving its function (biodegradable stents). This article discusses applicability of the current laser-cutting-based stent manufacturing process for making biodegradable stents: from materials production to stent fabrication until implantation. It covers some practical and technical points extracted from literatures and authors experiences with clinicians and industrialists to be considered in developing metallic biodegradable stents.

Abstract: The present study investigated a novel surface modification on metal coronary stent for antibody immobilization. Methods: 316L stainless steel stents were surface modified with protein coatings. An Anti-DNA antibody was covalently bound to the protein surface using a bi-functional cross-linking agent SPDP. The artwork and binding stability of protein coatings were evaluated by in-vitro eluting. The feasibility and stability of anti-DNA antibody covalently bound to the stent were evaluated by means of 125I labeling. Results: We observed that pre-treating the steel surface using diluted HCL and increasing the ratio of cross-linking agent caused significantly increased binding stability of the protein coatings (p﹤0.001). The amount of chemically coupled antibody on the stents was 8 times higher than that of physically absorbed control stents. The stability of chemically coupled antibody on the stent was significantly better than physically absorbed control. Conclusion: It is concluded that we optimized the technique of protein coating on stainless steel and achieved stable anti-DNA antibody immobilization, therefore enabled efficient and highly localized non-viral gene delivery.

Abstract: Almost half of the deaths in the European Union are a consequence of cardiovascular diseases, which can be reduced significantly by dietary changes, physical activity and suitable medications. Since changing lifestyle and healthcare is a slow process, a more efficient and quicker solution is to improve medical devices. Stents are mesh-structured implants, which support arterial wall and allow dilatation of the narrowed section. The material analyses of stents removed from cadavers allow further development and improvement of these special devices. Despite of the widespread application of stents, not many publications deal with their technical analysis and most of them have a medical approach. This paper presents a technical analysis of three stents removed from cadavers. The results may promote the evaluation of the stent development. Until now these kind of feedback was missing from the improvement cycle.

Abstract: This paper presents a comparative bibliographic study of different materials with elevated biomechanical biocompatibility regarding the stent-blood vessel interaction. Only the materials used in coronary stents’ manufacturing are considered: stainless-steel (316L), Cobalt-Chromium alloys (CoCrMo, CoNiCrMo), Nickel-Titanium alloys (Nitinol), Tantalum. The main characteristics that result from the stress-strain curve of each material are presented, as well as the biocompatibility and durability. The stainless-steel has good mechanical properties, excellent biocompatibility and low price. Cobalt-Chromium alloys have excellent mechanical properties, excellent biocompatibility, acceptable shape memory properties, but high density and low flexibility. The Nitinol represents the best choice, with excellent mechanical properties, excellent biocompatibility, good corrosion resistance, high flexibility (super-elastic behavior), low density, but high price. Tantalum alloys present the best biocompatibility and high flexibility, but the mechanical properties are relative modest.

Abstract: Objectives: Numerical stress intensity factors (SIFs) computation for several fabrication defect geometries in coronary stents. XFEM crack initiation and propagation was also performed. Methods: The model represents a self-expandable coronary stent, made from a shape memory alloy (L-605). Several flaw shapes are considered. The analysis was performed using the ABAQUS code. The loads and boundary conditions simulate the interaction between the blood vessels and stents, immediately after the angioplasty was performed. The mesh contains 3d stress hexahedral elements. For global stress and strain distributions, the model of a complete stent was used. For crack propagation analysis and SIF determination, the model represented a single segment of the stent. The stress intensity factors were computed using the contour integral method. Results and conclusions: The stress and strain fields highlight the negative effects of crack initiation and propagation on the residual life of the stent. Furthermore, by compromising the structural integrity of the stent, large strains may occur, thus increasing the risk of restenosis and further stenosis-related complications. The stress intensity factors indicate the most dangerous locations for the flaws (cracks), as well as the most dangerous geometries.