Abstract： The first generation scaffolds of bare metal stents （BMS） and the second generation of drug eluting stents （DES） have been widely used in the treatment of coronary heart diseases. However, long term incidences of major adverse cardiovascular events and revascularization treatments are still high because of in-stent re-stenosis and thrombosis. These may be caused by chronic inflammations and vascular wall damages due to persistent metal stents stimulation. What’s more, the eluting drugs within metal stents could also disturb normal growth of vascular endothelial cell, intima, tunica media, smooth muscle and epimysium. Therefore, in order to meet these demands several fully biodegradable scaffolds and drug carried stents have been manufactured using polymers polyester, polycarbonate and polyphosphate, etc. Among them, the security and histo-and hemo-compatibilities of coronary scaffolds made from poly-lactic acid （PLA）, poly-glycolic acid（PGA）, chitosan as coating, poly-caprolactone （PCL） and other copolymer like poly-lactic-co-glycolic acid （PLGA） have been testified to be sound. Nevertheless, there exist several different shortages for these stents such as tensile strength deficiency and slow degradation. PLA is hard and brittle with slow degradation, while PGA is soft with insufficient support force and fast degradation. Whether stents degrade too fast or too slow, they could not supply sufficient strength and effective support after implantation, and also they may cause target vascular injuries and elastic shrink inducing restenosis and thrombosis in long terms. Using optimized molar ratio component of PLA and PGA with chitosan coating, we can get sound composite materials with better biocompatibility, moderate degradation （approximately 3 - 6 months of completedegradation）, adequate mechanical strength, lower inflammatory response and good range of extension, and establish an experiment ground for fully biodegradable vascular scaffolds fabrication.
This paper adopted UG8.0 to bulid the stent and blood vessel models. The models were then imported into the finite element analysis software ANSYS. The simulation results of ANSYS software showed that after endothelial stent implantation, the velocity of the blood was slow and the fluctuation of velocity was small, which meant the flow was relatively stable. When blood flowed through the endothelial stent, the pressure gradually became smaller, and the range of the pressure was not wide. The endothelial shear stress basically unchanged. In general, it can be concluded that the endothelial stents have little impact on the flow of blood and can fully realize its function.
Cardiovascular disease is one of the most common causes of death. Coronary artery stent implantation has been the most important method to cure coronary disease and inhibit angiostegnosis. However, restenosis and thrombus at the site of implanting cardiovascular devices remains a significant problem in the practice of interventional cardiology. Recently, lots of studies have revealed that endothelial impairment is considered as one of the most important mechanisms contributing to restenosis. As a result, the method of accelerating endothelial regeneration at the injury site could prevent restenosis and thrombus. Considering the surface modification of cardiovascular stent implantation, this paper summarizes the progress on this direction, especially for the prevention of cardiovascular restenosis. Furthermore, this paper also proposes the methods and the future developing prospects for accelerating in vivo re-endothelialization at the site of intravascular stent with different biological molecules.
The current finite element analysis of vascular stent expansion does not take into account the effect of the stent release pose on the expansion results. In this study, stent and vessel model were established by Pro/E. Five kinds of finite element assembly models were constructed by ABAQUS, including 0 degree without eccentricity model, 3 degree without eccentricity model, 5 degree without eccentricity model, 0 degree axial eccentricity model and 0 degree radial eccentricity model. These models were divided into two groups of experiments for numerical simulation with respect to angle and eccentricity. The mechanical parameters such as foreshortening rate, radial recoil rate and dog boning rate were calculated. The influence of angle and eccentricity on the numerical simulation was obtained by comparative analysis. Calculation results showed that the residual stenosis rates were 38.3%, 38.4%, 38.4%, 35.7% and 38.2% respectively for the 5 models. The results indicate that the pose has less effect on the numerical simulation results so that it can be neglected when the accuracy of the result is not highly required, and the basic model as 0 degree without eccentricity model is feasible for numerical simulation.
Coronary atherosclerotic heart disease is a serious threat to human life and health. In recent years, the main treatment for it is to implant the intravascular stent into the lesion to support blood vessels and reconstruct blood supply. However, a large number of experimental results showed that mechanical injury and anti-proliferative drugs caused great damage after stent implantation, and increased in-stent restenosis and late thrombosis risk. Thus, maintaining the integrity and normal function of the endothelium can significantly reduce the rate of thrombosis and restenosis. Stem cell mobilization, homing, differentiation and proliferation are the main mechanisms of endothelial repair after vascular stent implantation. Vascular factor and mechanical microenvironmental changes in implanted sites have a certain effect on re-endothelialization. In this paper, the process of injury caused by stent implantation, the repair mechanism after injury and its influencing factors are expounded in detail. And repairing strategies are analyzed and summarized. This review provides a reference for overcoming the in-stent restenosis, endothelialization delay and late thrombosis during the interventional treatment, as well as for designing drug-eluting and biodegradation stents.
Objective To analyze the near-term clinical efficacy of two different surgical procedures (Sun's procedure and Debranching combined endovascular stent-graft procedure) to cure Stanford type A aortic dissection, and summarize the clinical experience to help better master the indications of the two surgical procedures. Methods We retrospectively analyzed the clinical data of 46 patients with Stanford A aortic dissection in our hospital between September 2014 and September 2017. There were 39 males and 7 females at age of 20–74 (48.67±11.80) years. According to different surgical methods, the patients were divided into a Sun's procedure group (26 patients) and a debranching combined endovascular stent-graft procedure group (20 patients). The clinical effect of the two groups was compared. Results The debranching combined endovascular stent-graft procedure group was significantly superior to the Sun's group in cardiopulmonary bypass (CPB) time, aortic cross clamp(ACC) time, intraoperative urine output, postoperative mechanical ventilation time, postoperative 24 h volumes of drain, CICU time, renal function recovery of postoperative 72 h and total hospital stay(P<0.05). The incidence of transient neurological damage after operation in the debranching combined endovascular stent-graft procedure group was significantly lower than that of the Sun's procedure group(P<0.05). The follow-up time ranged from 3 to 36 months. And the follow-up rate was 90.5%. One patient in the Sun's procedure group died of serious pulmonary infection postoperative 30 days. One patient in the debranching combined endovascular stent-graft group was found to have internal leakage in the early postoperative examination and disappeared after 6 months. Sun's procedure group did not find endoleak. All patients during the follow-up time did not appear brain, coagulation disorders, stroke, paraplegia, upper limb ischemia and other complications. Conclusion For Stanford type A aortic dissection, debranching combined surgery may have the risk of postoperative endoleak, but the overall effect is superior to Sun's operation. Therefore, debranching combined surgery should be preferred for the treatment of this type of dissection.
New biodegradable intravascular stent can reduce risk of foreign bodies retained, thus, it is widely concerned and some of the products have been introduced into the clinic. However, the characteristic of biodegradable may lead to more safety concerns associated with thrombosis. To ensure the safety, the thrombus formation experiment in vivo needs to be carefully designed and evaluated based on GB/T 16886.4 standard, but current standard do not provide explicit testing and evaluating methods. Establishing animal model with experimental pigs, the study compares biodegradable coronary stents and metal stents by simulating clinical implantation in vivo on the thrombus formation in the implanting process, and after the short-term and long-term implantation. The evaluation methods include gross observation, digital subtraction angiography intraoperative analysis, optical coherence tomography analysis, scanning electron microscopy and so on. The results show that combining these methods could comprehensively evaluate the whole process of the thrombus formation from the beginning of implantation to the end of preclinical animal experiments, so that, it may better predict the clinical thrombosis risk, and the selection of the control was very important. The study tries to use the comparison examples of thrombosis on the new medical instrument to provide the clue for thrombosis evaluation in vivo on similar instruments and show the methodology on the preclinical evaluation.
In vitro 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.
To solve the problem of stent malapposition of intravascular stents, explore the design method of intravascular body-fitted stent structure and to establish an objective apposition evaluation method, the support and apposition performance of body-fitted stent in the stenotic vessels with different degrees of calcified plaque were simulated and analyzed. The traditional tube-mesh-like stent model was constructed by using computational aided design tool SolidWorks, and based on this model, the body-fitted stent model was designed by means of projection algorithm. Abaqus was used to simulate the crimping-expansion-recoil process of the two stents in the stenotic vessel with incompletely calcified plaque and completely calcified plaque respectively. A comprehensive method for apposition evaluation was proposed considering three aspects such as separation distance, fraction of non-contact area and residual volume. Compared with the traditional stent, the separation distances of the body-fitted stent in the incompletely calcified plaque model and the completely calcified plaque model were decreased by 21.5% and 22.0% respectively, the fractions of non-contact areas were decreased by 11.3% and 11.1% respectively, and the residual volumes were decreased by 93.1% and 92.5% respectively. The body-fitted stent improved the apposition performance and was effective in both incompletely and completely calcified plaque models. The established apposition performance evaluation method of stent considered more geometric factors, and the results were more comprehensive and objective.
ObjectiveTo compare the improvement of clinical symptoms and patency of stents in patients with left and right non-thrombotic iliac vein compression syndrome (NIVCS) after endovascular stent therapy. MethodsThe clinical data of patients with NIVCS admitted to the First Affiliated Hospital of Chongqing Medical University from January 2016 to January 2021 were analyzed retrospectively. The venous clinical severity score of the patients’ veins before therapy and on month 12 after therapy was analyzed. At the same time, the patencies of stents on month 1, 3, 6, and 12 after stenting were also analyzed. ResultsA total of 164 patients with NIVCS were collected, including 144 left NIVCS and 20 right NIVCS. The surgical technique success rate of endovascular stent therapy was 100% (164/164). There was no statistical difference of the venous clinical severity score between the patients with left and right NIVCS on month 12 after therapy (t=1.265, P=0.208), but the venous clinical severity score of left and right NIVCS patients on month 12 after therapy were lower than those before therapy (t=27.534, P<0.001; t=10.047, P<0.001). The accumulative one-stage stent patency rate on month 12 after therapy was 96.5% and 94.7% in the patients with left and right NIVCS, respectively (χ2=0.160, P=0.689). After the stent was fully supported and completely covered the extent of the lesion, the short-term (within 12 months) stent patency rates of the patients with different compression site of the iliac vein, as well as type, diameter, and length of stent placement had no statistical differences (P>0.05). ConclusionFrom the results of this study, whether left NIVCS or right NIVCS, endovascular stent therapy is safe and effective.