Papers by Keyword: Stent

Abstract: Objective: To investigate the effects of TGFα-SAP on the inhibition of neointimal hyperplasia of rat which suffered from common carotid arterial injury. Methods: Saporin and TGFα were conjugated by using N-succinimidyl-3 (2-pyridyldithio) propionate. seventy rats were divided into two groups at random, the TGFα-SAP treated group was treated with local injection of TGFα-SAP (5μg/kg) after injury, and the control group was treated with saline. PCNA analysis and TUNEL analysis were performed. Results: Compared to the control group, the TGFα-SAP treated group showed a significant inhibition of intimal thickness and exhibited a lower P/A ratio and a higher rate of apoptosis. Conclusion: TGFα-SAP, as a potential stent coating material, could inhibit neointimal hyperplasia by inhibiting the proliferation and promoting the apoptosis of smooth muscle cells in the neointima.

Abstract: Drug loaded polyurethane (PU) thin layer was prepared on the silicone tube by electrospinning technique. Microstructure of the PU layer was varied from nanoporous web to dense coating depending on the polymer solution concentration and the amount of drug loaded. It can be easily adjusted the coating thickness and porosity accurately and controlled the drug loading and releasing properties. However, adhesive strength between PU layer and silicone tube was very weak and easily broken away and white turbidity also another important problem. So, surface of silicone tube was atmospheric-pressure plasma (APP) treated for improving the adhesive and removing white turbidity phenomenon.

Abstract: Objectives: This paper presents a numerical fatigue life assessment of a self-expandable Nitinol stent. The analysis was performed using the ANSYS 11 software. Methods: Stent durability is an issue which must be addressed during the design of implants. Given the corrosive properties of blood and the cyclic loads that are applied on the stent (the cyclic variation of blood pressure), the determination of fracture parameters and fatigue characteristics of the implant is highly recommended. Breaking of the stent’s wire is particularly dangerous because it can cause the dislocation of a piece of stenotic plaque, which in turn can block a smaller artery, causing a heart attack. On the other hand, any discontinuity in stent structure acts as an accumulating place for stenosis particles, significantly shortening the life of the implant. The stent consists of a cylindrical tube 22.42 mm long, with a diameter of 8.3 millimeters. The wire section is square, 0.2x0.2 millimeters. The stent is only subjected to the pressure generated by the stenoted arterial wall. This evenly distributed pressure is defined at the outer surface of the stent and has a value of 2.5 MPa, corresponding to a 56% blood vessel stenosis. This way, the most severe loading conditions for the stent could be simulated. The stress distribution was then used to asses the fatigue life of the stent. Results and conclusions: The results showed that, in normal conditions (with the maximal internal pressure of 139 mm Hg = 18533 Pa), no damage appears on the stent after 10⁷ cycles.

Abstract: In this study, the tube sinking process for manufacturing the micro Ti-0.2Pd tube (2.4 mm external diameter, 0.4 mm thickness) was simulated by finite element analysis. The external diameter of the initial tube was 5.0 mm. In order to simulate the tube sinking process, the flow stress equation was deducted from the result of the tensile test and friction coefficient was indirectly obtained through the parameter studies. The simulation results showed the simulation error according to the change of diameter predicted to be less than 2%. The defect of the internal surface by stress was found through the experiment result.

Abstract: The stent is commonly used to support blood vessels to avoid blood obstruction. Its tubular structure is a combination of micro periodic structures. The stent is expanded uniformly due to its internal pressure during the implantation process until plastic deformation occurs. In this article, the simulation of a representative model with application of the proposed periodic boundary conditions is performed by using ABAQUS/Explicit package and Matlab code. To make a comparison, the entire model of the same type stent with general boundary condition is also analyzed. The numerical results show that the deformation and stress distribution calculated by the representative model is a little higher than those of the entire model, but their overall results agree well with each other. Therefore, the numerical results of the entire stent can be obtained by a simple geometrical tessellation of the deformed representative models. The advantage of this method is that it can significantly reduce the modeling and computing time for analyzing expansion of vessel stent.

Abstract: Stents are medical implants, which are applied to keep cavities in the human body open, e.g. blood vessels. Typically they consist of tube-like grids of suitable metal alloys. Typical dimensions depend on their applications: outer diameters in the mm-range and grid bar thickness in the 100 µm range. Before implantation, stents are compressed (crimped) to allow implantation in the human body. During implantation, stents are expanded, usually by balloon catheters. Crimping as well as expansion causes high strains and high stresses locally in the grid bars. These strains and stresses are important design criteria of stents. Usually, they are calculated numerically by Finite Element Analysis (FEA) [1,2]. The XRD-sin²ψ-technique is applied for in-situ-determination of stress conditions during crimping and expansion of stents of the CoCr-alloy L-605. This provides a realistic characterization of the near-surface stress state and an evaluation of the numerical FEA results. XRD-results show an increasing compressive load stress in circumferential direction with increasing stent expansion. These findings correlate with the numerical FEA results. Further residual stresses after removing the expansion device have been measured.

Abstract: The 316L stainless steel stent was analyzed about the effect on interaction with plaque and vessels and blood flow during and after implantation using finite element method (FEM) and computational fluid dynamics (CFD). The results showed that tilted ends are likely to damage the intima which may stimulate thrombus formation and neointimal hyperplasia and will cause the restenosis. Stagnant zones formed by the stent may cause the backflow phenomenon, which also contribute to the important elements of in-stent restenosis (ISR).

Abstract: Stents have been used for the treatment of cardiovascular diseases and are often placed inside coronary arteries. The manufacture of metal stents is a challenging issue because of the features, like geometry and the material of stents. An improved manufacturing process of stents is presented. The proposed processes consist of the following steps: boring and polishing, laser cutting, vacuum annealing and surface finishing (ultrasonic cleaning, acid pickling, and electrolytic polishing). The precision boring operation is used to obtain the required wall thickness from off-the-shelf seamless tube. The laser cutting is performed to change the shape of the stent, and the finishing operations is selected to modify the surface features, like smoothness and texture of stents. 316LVM stainless steel sample with an outside-diameter of 3 mm, a wall thickness of 0.1 mm, and a length of 25 mm, had been manufactured and demonstrated the proposed manufacture technology. The surface roughness of a stent manufactured is the value of Ra 14.3 nm which basically meets the design requirement for further performance evaluation. It is hoped that the above finding can be used for future study of stents.

Abstract: Biodegradable metals have been proposed for temporary implants such as coronary artery stent and internal bone fixators. During implantation, a stent is inserted and expanded by using a catheter into a narrowed coronary artery and is subjected to mechanical stress in a corrosive body fluid environment, a condition where stress corrosion cracking may occur. This letter reports an experimental work to verify the susceptibility of Fe-35Mn alloy, a proposed alloy for biodegradable coronary stent, to stress corrosion cracking under a pseudo-physiological condition.

Abstract: Calcium phosphates films were deposited onto pipes and stents of nitinol alloys by an electrolytic deposition (ELD) method. Monocalcium phosphate (Ca (H₂PO₄)₂·H₂O) solutions were used as the electrolyte, and electric depositions were carried out at the constant cathode current of 1.59 mA/cm² at 65°C for 60 min. From the deposition on nitinol pipes, deposition rates were changed in 15 minutes and the precipitates were identified to be octacalcium phosphate (Ca₈H₂(PO₄)₆·5H₂O) and dicalcium phosphate anhydrous (CaHPO₄). The electrolytic depositions on the nitinol alloys were useful for the formation of calcium phosphates films on the complex shape of stents.