Papers by Keyword: Stent

Abstract: The effects of alloy chemistry and heat treatment on the microstructure and mechanical properties of Ti-Nb-Zr-Mo-Sn near  type titanium alloys have been investigated. Near β titanium alloys consisting of non-toxic alloying elements Mo, Nb, Zr, Sn possess a low Young’s modulus, and moderate strength and plasticity. As the hot rolled TLM alloy (Ti-25Nb-3Zr-3Mo-2Sn) possesses high strength and low Young’s modulus a detailed investigation is performed for this alloy. Solution treatment of the hot rolled TLM alloy reduces strength and increases ductility without affecting the Young’s modulus. Ageing of the solution treated TLM alloy reduces elongation and increases the Young’s modulus with little change in strength. Both solution treated and aged conditions show features of two stage yielding associated with a strain induced martensitic transformation.

Abstract: A three-layer coating for stents with a nanostructured surface of calcium phosphate (CaP) is pre-sented. The coating stack consists of (a) a TiNbN layer deposited by physical vapour deposition and acting as diffusion barrier against allergenic ions, (b) a SiO2 xerogel layer providing good adhesion properties and designing the nanoporosity of the outer CaP layer (c) precipitated electrochemically. The verification of the SiO2-layer (and therewith its influence onto adhesion and structure of the outer CaP layer) succeeded only by use of XPS because of the very small amount of the xerogel. SEM results verified a homogeneous nanoscale nanoporous structure of the CaP coating. It is char-acterised by high adhesion strength. If applied for stent covering the nanoscale CaP coating has promising properties to initiate rapid endothelium formation and reduced risk of restenosis.

Abstract: Currently, a minimally invasive surgery called stenting is extensively used to increase the lumen of partially obstructed arteries. Unfortunately, restenosis, a postoperative phenomenon in which the lumen of the artery is reduced due to a traumatism of the artery, is still a concern. The most popular solution that has been adopted by stent manufacturers comprises drug-eluting stents. This paper presents a new stent concept in which the treatment of restenosis is carried out from a completely different angle. Indeed, instead of traumatizing the artery, and then trying to control restenosis with drugs, the new stent minimizes the traumatism of the artery by expanding itself, not instantaneously, but progressively, and in a controlled manner. To achieve this, a nitinol stent over which a series of polymer rings are installed tries to reach a fully deployed configuration, but the polymer rings, which act as a retainer, become soft over time due to creeping. Thus, after the initial deployment in the artery, the stent continues its expansion autonomously over an extended period of time (a few weeks). It is believed that the artery has enough time to adapt to the expansion, leading to minimum traumatism. This paper presents the stent design.

Abstract: This paper reported a newly designed retrievable urethral stent used in treatment of urethral strictures. The spiral urethral stent is made of Poly (l-lactide) (PLLA), adding barium sulphate (BaSO4) to certain content, which can be displayed precisely under X-ray after implanted in body. The stent was clinically tested in 32 patients with recurrent urethral strictures and was left in the urethra for 5 to 12 months. The response to the effect of the stent was assessed using symptom scores, peak flow rate (Qmax), residual urine volume (RUV), stent degradation, infection and outcome. During the treatment, there were not any inflammations found. The mechanical properties of the stent are almost the same as those of the PLLA stent without BaSO4. Improvements in patient symptom score, mean Qmax and RUV were significant at the 18 month follow-up. The infection was not observed. The stent was taken out easily through urethral forceps. In no patient was the stent obstructed by incrustation for up to 1.5 years.

Abstract: Recently, the intravascular therapy using microcoils and stents to treat aneurysms has attracted researcher’s interest. In this study, in order to evaluate the effects of the stents, a numerical simulation of two-dimensional flows has been carried out for a pipe with a model of an aneurismal sac. Using aneurismal models with different inclined angles to the pipe, inflow conditions with steady states or pulsations have been applied in the range of Reynolds number in human blood flows. First, the computational results are compared with experiments under the steady inflow condition, which has shown the reliability of the numerical simulation. Furthermore, the mechanism of flows with an aneurismal model is discussed in the case with or without a stent, and consequently the effect of the stent is clarified.

Abstract: A nanoporous calcium phosphate (CaP) coating on metallic surfaces is presented. The coating consists of a stack of (a) a TiNbN layer deposited by physical vapor deposition and acting as diffusion barrier against allergenic ions, (b) a SiO2 xerogel layer providing good adhesion properties and designing the nanoporosity of the outer CaP layer (c) precipitated electrochemically. SEM results verified a homogeneous nanoscale porous structure of the CaP coating. It is characterized by a high adhesion strength. If applied to stent covering the nanoporous CaP coating has promising properties to initiate rapid endothelium formation and reduced risk of restenosis.

Abstract: Titanium oxides films were deposited on tensile sample and vascular stents made of 316L stainless steel by unbalanced magnetron sputtering. The effects of structures, deposition temperature, Ti interlayer and thickness on the adhesion of titanium oxide films were investigated by tensile tests. The results revealed that the structure of the Ti-O films affect their adhesion dramatically. TiO film is brittle and fragile, lacking ability of deformation. Therefore its adhesion was worse than that of TiO2 film. The higher substrate temperature was helpful to improve adhesion of film, the adhesion of the TiO film deposited at 673K was better than those of the TiO films deposited at 323K and 473K. The adhesion of the TiO film with Ti interlayer was better than the one without interlayer. The introduction of Ti interlayer was beneficial to adhesion of film. The adhesion of thinner TiO2 film was better than that of thicker one. TiO2 film deposited on stents had good adhesion. After expansion, the film didn’t crack and peel off. TiO2 film has potential application on the vascular stents for improving its blood compatibility.

Abstract: In this study, newly synthesized zwitterionic PEG was grafted on Nitinol alloy using oxidation treatment. The surface property and blood compatibility of surface-modified Nitinols were examined. The results of surface analysis showed that the contact angle and the ratio of oxygen to carbon significantly decreased with Nitinol alloys. The total amount of fibrinogen (0.095 μg/cm2) adsorbed onto TiNi-PEG2K-N+-S- was lower than that of TiNi control (0.12 μg/cm2). The platelet adhesion decreased in the order of TiNi control > TiNi-MPEG2K > TiNi-PEG2K-N+-S. Particularly, zwitterionic PEG with PEG2K was proven better than any others. The results indicated that zwitterionic PEG surface could significantly suppress platelet adhesion and protein adsorption as compared to other samples. The present study suggested that grafted zwitterionic PEG structure may possess improved blood compatibility.

Abstract: In-stent restenosis is the result of a healing process that induces neointimal hyperplasia though mechanisms that are still not understood. The purpose of this study was to analyze the early histologic consequences and the kinetics of the healing process for a 72-hours period after stent implantation in an organ culture model. MTT-tests show that the vessel could maintain activity in the organ culture system. The vessel with stent had a different morphology and inflammatory molecule release compared with the normal vessel. So there could have direct relationships between inflammatory release and neointimal hyperplasia. The organ culture system can provide valuable information for studies of in-stent restenosis after stent implantation, especially for evaluation of new stents, such as drug-coated or other surface-modified stents.

Abstract: In Western countries, cardiovascular disease is the most common cause of death, often related to atherosclerosis which can lead to a narrowing of the arteries. To restore perfusion of downstream tissues, an intravascular stent (i.e. a small tube-like structure) can be deployed in the obstructed vessel. The vast majority of stents are balloon expandable and crimped on a folded balloon to obtain a low profile for deliverability and lesion access. Several studies have exploited the finite element method to gain insight in their mechanical behaviour or to study the vascular reaction to stent deployment. However, to date – to the best of our knowledge – none of them include the balloon itself in its actual folded shape. Furthermore, literature on the effect of the crimping process on the expansion behaviour of the stent is even scarcer. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with data provided by the manufacturer and consequently our approach could be the basis for new realistic computational models of angioplasty procedures. The plastic deformation, prior to the stent expansion and induced by the crimping procedure, has a minor influence on the overall expansion behaviour of the stent but nevertheless influences the maximum von Mises stress and nominal strain. The maximum von Mises stress drops from 440 N/mm² to 426 N/mm² and the maximum nominal strain value lowers from 0.23 to 0.22 at the end of the expansion phase when neglecting the presence of the residual stresses. Depending on the context in which to use the developed mathematical models, the crimping phase can be discarded from the simulations in order to speed up the analyses.