Three-dimensional printed 316L stainless steel cardiovascular stent's electrolytic polishing and its mechanical properties / 生物医学工程学杂志

The interventional therapy of vascular stent implantation is a popular treatment method for cardiovascular stenosis and blockage. However, traditional stent manufacturing methods such as laser cutting are complex and cannot easily manufacture complex structures such as bifurcated stents, while three-dimensional (3D) printing technology provides a new method for manufacturing stents with complex structure and personalized designs. In this paper, a cardiovascular stent was designed, and printed using selective laser melting technology and 316L stainless steel powder of 0-10 µm size. Electrolytic polishing was performed to improve the surface quality of the printed vascular stent, and the expansion behavior of the polished stent was assessed by balloon inflation. The results showed that the newly designed cardiovascular stent could be manufactured by 3D printing technology. Electrolytic polishing removed the attached powder and reduced the surface roughness Ra from 1.36 µm to 0.82 µm. The axial shortening rate of the polished bracket was 4.23% when the outside diameter was expanded from 2.42 mm to 3.63 mm under the pressure of the balloon, and the radial rebound rate was 2.48% after unloading. The radial force of polished stent was 8.32 N. The 3D printed vascular stent can remove the surface powder through electrolytic polishing to improve the surface quality, and show good dilatation performance and radial support performance, which provides a reference for the practical application of 3D printed vascular stent.

Design and Finite Element Analysis of a Novel Retrievable Vascular Stent / 医用生物力学

Objective In order to avoid early restenosis after drug-eluting stent (DES) implantation, the retrievable structure of the NiTi alloy stent and its biomechanical analysis were studied. Methods The geometric models of the retrievable vascular stent and the retrieval system were established. The retrieval part of the stent consisted of four symmetrically distributed tendons, which were designed as circular meshes. The distribution of the maximum strain during stent compression and its uniformity during compression and self-expansion were analyzed, and the simulation experiments of the retrieval process were also performed. Results The maximum strain of the stent was 3.7% and the index of non-uniformity (INU) was 0.62% when the stent was compressed to the minimum size. While the IBU was 1.31% after the self-expansion process completed. The maximum strain was 1.2% when half of the stent was retrieved into the outer sheath. Conclusions The stent could be safely and successfully retrieved into the outer sheath as the strain was within the bearable range of the material and the compression and self-expansion process was relatively uniform. The research findings provide important references for structural design, biomechanical analysis and potential clinical applications of the novel retrievable vascular stent.

In vitro experimental study on the mechanical properties of biodegradable polymer stents / 生物医学工程学杂志

experimental test for mechanical properties of a vascular stent is a main method to evaluate its effectiveness and safety, which is of great significance to the clinical applications. In this study, a comparative study of planar, V-groove and radial compression methods for the radial support property test were performed, and the effects of compression rate and circumferential position on the test results were conducted. Based on the three-point bending method, the influences of compression rate and circumferential position on flexibility were also explored. And then a best test proposal was selected to evaluate the radial support property and flexibility of the three self-designed stents and the comparative biodegradable vascular stent (BVS) (BVS1.1, Abbott Vascular, USA) with different outside diameters of 1.4 mm, 1.7 mm and 2.4 mm. The results show that the developing trends of the compression load with the compression displacement measured by the three radial support property test methods are the same, but normalized radial force values are quite different. The planar compression method is more suitable for comparing the radial support properties of stents with different diameters and structures. Compression rate has no obvious effect on the testing results of both the radial support property and flexibility. Compression circumferential position has a great impact on testing radial support property with the planar or V-groove compression methods and testing flexibility with three-point bending method. The radial support properties of all the three self-designed stents are improved at a certain degree compared to that of the BVS stent. The study has better guide significance and reference value for testing mechanical properties of vascular stents.

Stent implantation for the treatment of central venous obstruction in hemodialysis patients with arteriovenous fistula: analysis of its clinical value / 介入放射学杂志

Objective To discuss the feasibility and clinical value of percutaneous transluminal stenting (PTS) for the treatment of central venous obstruction (CVO) in hemodialysis patients with arteriovenous fistula (AVF).Methods The clinical data of 10 hemodialysis patients with AVF complicated by CVO were retrospectively analyzed.Clinically,all patients presented as swollen hand syndrome.Preoperative or intraoperative digital subtraction angiography (DSA) was performed to determine the obstruction site,and based on the disease condition the appropriate surgical approach was employed.For patients having thrombus formation,catheter-directed thrombolysis (CDT) was carried out first.For patients having severe stenosis or occlusion of veins,pre-expansion with small diameter balloon was employed before PTS.For the remaining patients,PTS was directly performed.All patients were regularly followed up after operation.Results DSA showed that brachiocephalic vein occlusion and/or occlusion or stenosis of subclavian vein,internal jugular vein and superior vena cava were observed in 5 patients who had history of internal jugular vein catheterization,while localized severe stenosis of medial segment of AVF-side subclavian vein was detected in the other 5 patients who had no history of internal jugular vein catheterization.The technical success rate of PTS was 100％ (10/10).A total of 19 stents were implanted in the 10 patients.Seven months after the treatment,one patient developed in-stent re-stenosis,and PTS had to be carried out again.Primary patcncy rates at 6 months and 12 months after the treatment were 100％ (8/8) and 75％ (3/4) respectively.Conclusion In hemodialysis patients with AVF,CVO is mainly characterized by obstructive or severely stenotic lesions.PTS carries higher success rate with satisfactory short-term and mid-term effect,its complications are slight and mild,and the technique is safe and feasible.Therefore,PTS can be used as the preferred treatment method.

Propuesta de modelo de trauma vascular mediante la caracterización mecánica de prótesis endovasculares (stents) a través del análisis estructural con técnicas FEA / Proposed model of vascular trauma by mean of mechanical characterization of endovascular prostheses (stents) based on structural analysis by FEA

Resumen Objetivo Tras las evidencias acumuladas mediante el uso de técnicas de angioplastia con stents, surge la polémica sobre los factores que inciden en la respuesta final, ya que hay estudios que reportan reestenosis de la luz en el 30-40% alrededor de 6 meses luego de ser implantados, vinculándose como una de las causas al diseño del dispositivo. Este artículo propone la caracterización funcional de stents endovasculares, analizando su influencia mecánica en el sistema vascular y prediciendo los factores de trauma implícitos en el lecho de los vasos. Métodos Utilizando modelos computacionales de prótesis endovasculares tipo stents, mediante técnicas Finite Elements Analysis, se procedió al análisis estructural de dichos dispositivos con el fin de predecir el comportamiento mecánico y el trauma vascular. Para ello, las prótesis fueron consideradas estructuras tubulares compuestas por múltiples eslabones que están sometidos a cargas de presión, que se reflejan como concentradores de esfuerzos. Resultados El estudio permitió visualizar cómo se ajusta la geometría del stent a las diferentes cargas, obteniéndose una aproximación a la respuesta de interacción "sólido-sólido" entre el stent y la pared arterial. Así, se caracterizó el patrón de esfuerzos y se planteó un modelo conceptual que explica su incidencia mecánica en la interacción stent-vaso, para inferir en la funcionalidad del diseño del dispositivo. Conclusiones El modelo conceptual planteado permite determinar la relación entre las condiciones de interacción mecánicas del stent, y advierte sobre los efectos en lo que sería la operación del dispositivo en el ambiente vascular.

Abstract Objective The accumulated evidence on angioplasty techniques with stents has raised a controversy about the factors that influence the final vascular response. Indeed, several studies have shown there might be re-stenosis between 30% to 40% about 6 months after placement, relating to the design of the device as one of the main causes. This paper proposes the functional characterization of endovascular stents, analyzing its mechanical influence in the vascular system and predicting implicit traumatic factors in the vessel. Methods A structural analysis was made for several computational models of endovascular stents using Finite Element Analysis in order to predict the mechanical behavior and the vascular trauma. In this way, the stents were considered as tubular devices composed of multiple links under radial pressure loads, reflecting stress concentration effects. Results The analysis allowed to visualize how the geometry of stents is adjusted under several load conditions, in order to obtain the response of "solid-solid" interaction between the stent and the arterial wall. Thus, an analysis was performed in order to calculate stress, and a conceptual model that explains its mechanical impact on the stent-vessel interaction, was raised, to infer on the functionality from the design of the devices. Conclusions The proposed conceptual model allows to determine the relationship between the conditions of mechanical interaction of the stents, and warns about the effects in what would be the operation of the device on the vascular environment.

Simulation study on expansion process of vascular stent in realistic stenosis model / 医用生物力学

Objective To study the deformation and mechanical characteristics during expansion process of vascular stent in realistic stenosis model, so as to provide scientific references for interventional treatment and stent design. Methods The carotid vessel model and plaque model of patient were built by using 3D reconstruction method, and the stent model with I-shaped link was established by using Pro/E; ABAQUS/Standard was used to simulate the radial expansion (the first stage) and radial contraction (the second stage) of the stent in real stenosis model, and a realistic model of blood vessel with plaque was also established to make contrast test. Results In the first stage, radial expansion of the stent was formed. The maximum contact area was generated between the outer surface of the stent and the inner surface of the plaque/arterial wall, and the maximum stresses on the stent, plague and arterial wall were 515.000, 2.482, 1.053 MPa, respectively. In the second stage, the radial contraction of the stent resulted in “dog-bone” effect. Many gaps between the stent and vessel wall was formed, and the maximum stresses on the stent, plague and arterial wall were 464.500, 0.954, 0.316 MPa, respectively. In contrast test, the maximum stresses on stenotic vessel and stent were 0.9, 414.1 MPa in the second stage. Conclusions Compared with the model in contrast test, the stenosis model differentiating the component of vascular tissues is more consistent with the real situation of stenotic vessels, by more truly showing deformation and mechanical characteristics of the stent and blood vessel. The stent causes the maximum damage to plaque and inner wall of blood vessel in the first stage, while “dog-bone” effect of the stent is an important influencing factor that results in the gaps between the stent, plague and blood vessel. These research findings may provide significant guidance for selecting stent in interventional treatment and improving stent design.

Experiment and finite element analysis on amorphous carbon coatings delaminating from vascular stents / 医用生物力学

Objective To investigate the phenomenon of amorphous carbon coating delamination during crimping and expansion of the vascular stent, and study how to avoid such phenomenon from both material selection and dimension design of the stent. Methods Amorphous carbon coatings were deposited onto a bare metal stent by chemical vapor deposition method, and then to simulate the crimping and expansion process of the stent. Coating delamination at different regions of the stent was observed by scanning with electron microscope, and the force mechanism and influencing factors related with amorphous carbon coating delamination during stent crimping and expansion were analyzed by finite element method. Results The finite element results could perfectly agree with the experimental results. The thickness of amorphous carbon coatings determined the complexity, as well as the formation pattern of coating delamination at different regions of the stent. Larger elastic modulus of amorphous carbon coatings could cause the formation of coating delamination much easier to occur. Besides, the stent modulus would also have some impact with different influencing patterns at different regions on coating delamination. Conclusions In order to avoid coating delamination, the thickness of amorphous carbon coatings should be carefully designed, and the elastic modulus of both amorphous carbon coatings and stents should be rationally selected.

Design of a high performance vascular stent with asymmetric structures / 医用生物力学

Objective To design a novel high performance stent with preferable axial flexibility by using smaller strut thickness and less metal coverage which would not compromise its radial strength, so as to reduce the in-stent restenosis. Methods Based on researches about deformation properties of both the symmetric and asymmetric cell structures, the new stent structure was designed and analyzed through numerical simulation. The radial strength and bending stiffness tests were performed to evaluate the stent made by the new design. Results The proposed design possessed a higher radial strength, smaller metal coverage and good flexibility, which would be beneficial for the reduction of in-stent restenosis. Conclusions The asymmetric structure-based stent design method is effective, by which a high performance stent design can be obtained.

Vascular Interventional Procedures Often Encountered by Primary Physicians

Among various vascular interventional procedures, there are some procedures of vascular recanalization often encountered by primary physicians in clinical practice. These are percutaneous transluminal angioplasty (PTA) and stent application in the lower extremity ishemia, catheter-directed thrombolysis with PTA, stenting for iliofemoral deep vein thrombosis, and interventional management of arteriovenous fistula and graft for hemodialysis access. PTA and stent are safe and effective treatment for iliac arterial stenosis and occlusion with a good long-term patency rate. Long-term effectiveness of femoropopliteal stent is yet to be determined. Catheter-directed thrombolysis is a new emerging vascular intervention for acute iliofemoral deep vein thrombosis. May-Thurner syndrome can be effectively treated with thrombolysis in the iliofemoral vein followed by PTA ad stenting for the left iliac vein stenosis or occlusion. For the failing arteriovenous fistula or grafts in patients with hemodialysis, interventional radiologists can play an important role for the maintenance of the patency by percutaneous thrombolysis and balloon dilatation. It will be very helpful for the primary physicians to understand the role of the interventional radiologists and the indications, techniques, and results of those vascular interventional procedures often encountered in daily practice.

Use of a stent of shape memory alloy in angioplasty / 日本心臓血管外科学会雑誌

The surface-coated vascular stent of shape memory alloy was made for use of occlusion of pseudo-lumen of the dissecting aneurysm of the aorta, as the usage of shape memory alloy in angioplasty, and the metal flexible delivery catheter was also made for the introduction of the stent. In the present study, antithrombogenicity of the vascular stent was much improved by surface-coating with EPTFE and segmented polyurethane. The long-term usage of the stent was confirmed by radiological, macroscopic, and electron microscopic examinations. Moreover, the metal flexible delivery catheter was demonstrated to be of much benefit for the introduction of the surface-coated vascular stent of shape memory alloy.