• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.601-607
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• 2012

In this study, we performed computational fluid dynamic simulations to explore how the detailed design of drug-eluting stents affects both the flow field in the vicinity of the stent as well as the concentration of the eluted drug at the endothelial cell surface. Simulations were performed on three idealized stent geometries we developed and on geometries approximating three commercial stents,: Medtronic's Aurora stent, Cordis's BX Velocity stent, and Boston Scientific's Wallstent. An important contribution of the present study is the introduction of the stent effectiveness index (EI), which provides a quantitative assessment of stent performance and an objective basis for comparing the performance of different stents. Among the three commercial stents studied, our simulations have revealed that the BX Velocity stent is associated with the lowest in-stent EI values for the range of flow Reynolds numbers studied ($200{\leq}Re{\leq}800$). In addition to commercial stent designs, we investigated the EI in three idealized stents and determined that a spiral stent provides excellent performance (low EI) under all flow conditions investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1053-1060
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• 2011

This study is performed to determine the drug concentration profiles of drug-eluting stents (DES) for an ideal circular ring stent and intertwined stent models for various Reynolds numbers (Re = 200, 400, and 800). The Navier.Stokes equations coupled with the advection-diffusion equation are solved numerically in order to determine how the flow patterns and drug deposition are affected in the in-stent and post-stent regions where flow separation and recirculation occur. The presence of DES within the arterial segment affects the local drug distribution in the flow field. As a result, the drug concentration for the intertwined stent is higher over the in-stent region in comparison with the ideal stents. For a given stent geometry, the local drug concentration in the in-stent region decreases with Reynolds number, while for a given Reynolds number, the local drug concentration is relatively insensitive to the stent geometry. The results show that drug concentration along the arterial wall is significantly higher within the in-stent and post-stent regions for the intertwined stent geometry than for the ideal stent geometries.

• Journal of Biomedical Engineering Research
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• v.24 no.1
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• pp.37-44
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• 2003

This experimental study is aimed at evaluating the hydrodynamic performance of newly designed self-expandable graft stents under steady flow condition. Two graft stents with different coating materials and a bare TiNi metallic stent for comparison test were used in the experiment. Pressure variation and velocity distribution at the upstream and downstream of the stents were measured at flow rates of 5, 10, and 15 l/min, respectively. Pressure loss due to insertion of the stent increased with increasing flow rate exponentially as expected. At a flow rate of 15 l/min, pressure loss of Polyure-thane(PU)-coated graft stent was 6 times higher than that of TiNi metallic stent, while the pressure loss of a porous Polytetrafluoroethylene(PTFE)-coated graft stent was comparable to a bare TiNi metallic stent. Velocity profiles of the porous PTFE-coated graft stent were similar to those of a bare TiNi metallic stent regardless of flow rate. Furthermore, the velocity profile of PU-coated graft stent revealed an asymmetrical and relatively low central velocity at a higher flow rate than 10 1/min, expecially, where the effects resulted in increases of wall shear stress and normal stress. The worse hydrodynamic behavior of PU-coated graft stent than the other two stents might be attributed to formation of folds due to poor flexibility of coated material when inserting the graft stent into the pipe with a more smaller size, which later gave rise non-symmetry of flow area, increase of surface roughness and jet flow via the crevice between the stent and cylinder wall.

• Tuberculosis and Respiratory Diseases
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• v.59 no.1
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• pp.62-68
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• 2005

Background : The clinical results of a Natural stent in patients with a benign tracheobronchial stenosis were examined by comparing the clinical outcomes and complications of those patients who underwent Dumon and Natural stenting in the management of benign airway stenosis. Methods : The medical records of 94 patients (39 Dumon and 55 Natural stent) with a benign tracheobronchial stenosis were reviewed and analyzed. Results : Post-tuberculous stenosis was the leading indication for airway stenting (74%), which was followed by post-intubation stenosis (21%). After intervention, the dyspnea had improved among those patients who underwent Dumon (90%) and Natural (86%) stenting. After stabilizing the dyspnea, the stent could be successfully removed in half of the patients who underwent both Dumon (54%) and Natural (49%) stenting. During the 42 month follow-up period, the complication rate was similar in those patients who underwent Dumon and Natural stenting: migration (46% vs 53%), granulation tissue formation (36% vs 49%), mucostasis (21% vs 16%) and restenosis (51% vs 36%). Conclusion : The clinical results of Natural airway stent was similar to those of Dumon stent in the management of benign tracheobronchial stenosis.

• Journal of radiological science and technology
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• v.37 no.2
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• pp.109-116
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• 2014

Many studies have suggested that in the era of Drug-Eluting Stents(DES) are one of the causes of In-Stent Restenosis(ISR) of Stent Fracture(SF). The present study sought to evaluate clinical characteristics of patients with stent fracture after successful DES implantation. The 4,701 patients were selected for analysis who underwent a follow-up coronary angiography irrespective of ischemic symptoms. The overall incidence of SF was 32 patients(male:female=19:13, Av. age $62.44{\pm}9.8$year, 0.68%). Fractures of Sirolimus-Eluting Stents(SES), Paclitaxel-Eluting Stents(PES), Biolimus A9-Eluting Stents(BES), Everolimus-Eluting Etents(EES), Endothelial Progenitor Cell Capture Stent(EPC) and Zotarolimus-Eluting Stents(ZES) are accounted for 19(59.4%), 9(28.1%), 2(6.3%), 1(3.1%), 1(3.1%) and 0(0%) respectively. SF developed in the left Anterior Dscending(LAD) artery in 16 patients(50%) and in complex(type B2, C) lesions in 25 patients(69.4%). Ten patients were treated with heterogenous DES, the rest being treated with either homogenous DES(3 patients), plain old balloon angioplasty(3 patients), or conservative medical treatment(17 patients). None of the patients with SF suffered from cardiac death during a follow-up period of $32.9{\pm}12.4$ months. The overall rate of DES fracture over up to 3.7 years of follow-up was 0.68% with higher incidence in SES than in PES. SF frequently occurred in the LAD artery and in complex lesions. Of the patients with SF, coronary intervention was performed only when the binary restenosis lesion was significant. During the follow-up, patients with SF have continued on combination antiplatelet therapy. There is a very low rate of major adverse cardiac events(post-detection of SF), especially cardiac death associated with SF.

• Progress in Medical Physics
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• v.20 no.3
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• pp.119-124
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• 2009

Stents are frequently used throughout the human body. They keep pathways open in vascular or nonvascular duct for a long time. Therefore its stability is very important factor. In recent years, aconsiderable amount of research has been carried out in order to estimate mechanical properties of the stent such as expansion pressure behavior, radial recoil and longitudinal recoil using FEM (Finite element analyses). However, published works on simulation of stent fatigue behavior using FEM are relatively rare. In this paper, a nonlinear finite-element methodwas employed to analyses the compression of a stent using external pressure and fatigue behavior. Finite element analyses for the stent system were performed using NASTRAN FX. In conclusion this paper shows how the stent is behaved in the body, and its fatigue behavior.

• The Korean Journal of Pancreas and Biliary Tract
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• v.22 no.4
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• pp.165-171
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• 2017

Background/Aim: There is little data on whether plastic stents with a larger diameter are patent for longer than small stents in patients with bile duct cancer. The aim of this study was to compare the stent survival between 7-French (Fr) and 10-Fr plastic stents and evaluate the factors affecting stent survival. Methods: Patients with biliary obstruction due to biliary tract cancer were enrolled at Yonsei University Wonju College of Medicine from January 2010 to October 2014. Results: A total of 215 patients (7-Fr:10-Fr = 89:126 patients) were retrospectively enrolled. The primary tumor sites were common bile duct (n = 111), hilar (n = 45), and ampulla of Vater (n = 59). Rates of stent migration and stent obstruction were not different between the two groups. The median duration of stent survival was 3.3 months in the 7-Fr group and 5.9 months in the 10-Fr group (p = 0.543). The diameter of the stent did not have an effect on stent survival (hazard ratio 1.11, 95% confidence interval 0.71-1.73, p = 0.649). Conclusions: 7-Fr and 10-Fr stents have similar rates of stent migration and stent obstruction. The stent survival of 7-Fr was not inferior to 10-Fr stents in the management of biliary tract cancer.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.36-43
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• 2020

A biliant stent was fabricated using a magnesium alloy wire, a biodegradable metal. In order to control the fast decomposition and corrosion of magnesium alloys in vivo, magnesium alloy wires were coated with biodegradable polymers such as polycaprolactone (PCL), poly(propylene carbonate) (PPC), poly (L-lactic acid) (PLLA), and poly (D, L-lactide-co-glycolide) (PLGA). In the case of PPC, which is a surface erosion polymer, there is no crack or peeling compared to other polymers (PCL, PLLA, and PLGA) that exhibit bulk erosion behavior. Also, the effect of biodegradable polymer coating on the axial force, which is the mechanical property of magnesium alloy stents, was investigated. Stents coated with most biodegradable polymers (PCL, PLLA, PLGA) increased axial forces compared to the uncoated stent, reducing the flexibility of the stent. However, the stent coated with PPC showed the axial force similar to uncoated stent, which did not reduce the flexibility. From the above results, PPC is considered to be the most efficient biodegradable polymer.

• Journal of Hospice and Palliative Care
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• v.12 no.2
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• pp.49-55
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• 2009

Self expandable metal stent (stent) implantation of upper gastrointestinal (UGI) tract is now widely accepted for the palliation of obstructive symptoms caused by inoperable malignant UGI obstruction. With the technical progress and accumulation of clinical experiences, it became possible to perform the procedure easily, safely and effectively. However, clinicians should pay attention to the post-procedural care, because early or late complications such as ulceration, pain, bleeding, food impaction, perforation, migration or in-stent tumor growth could occur. In this review, several topics about stent placement in the UGI tract are discussed, such as major indications for stenting, kinds of stents, and post-procedural management.

• Tuberculosis and Respiratory Diseases
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• v.53 no.4
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• pp.431-438
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• 2002

Background : In order to investigate the usefulness and safety of Natural Stent, we performed this study in a canine model of tracheal stenosis induced using Nd-YAG laser. Materials and Methods : After tracheal stenosis was induced in 12 Mongrel dogs using Nd-YAG laser, either Dumon (n=6) or Natural (n=6) stent was inserted into the trachea. To assess the degree of stent migration and mucostasis, bronchoscopy was performed every week for 4 weeks, after which all stents were removed. One week after stent removal, tracheal stenosis was evaluated by bronchoscopy. Results : The degree of stent migration was not different between the dogs with Dumon stent ($3.0{\pm}0.8$) and those with Natural ($2.0{\pm}1.0$), nor was the degree of mucostasis, at Dumon ($1.7{\pm}0.5$) and Natural Stent ($1.5{\pm}0.6$), respectively. One week after stent removal, the degree of tracheal stenosis was not different between the Dumon ($1.5{\pm}0.5$) and the Natural group ($1.0{\pm}0.4$). In addition, there was no death and the degree of tracheal stenosis remained always within the safe limit (less than 2.0) in all animals. Conclusion : In a canine model of tracheal stenosis induced using Nd-YAG laser, the usefulness and safety of Natural Stent were similar to those of Dumon Stent. A clinical trial is necessary to document the usefulness and safety of Natural Stent in patients with tracheal stenosis.