• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.281-288
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• 2009

Numerical investigations have been conducted on the assessment of the performance of drug-eluting stent. Computational fluid dynamics is applied to investigate the flow disturbances and drug distributions released from the stent in the immediate vicinity of the given idealized stent in the protrusion into the flow domain. Our simulations have revealed the drug concentration in the flow field due to the presence of a drug-eluting stent within an arterial segment. Wall shear stress increases with Reynolds number for a given stent diameter, while it increases with stent diameter for a given Reynolds number. The drug concentration is dependent on both Reynolds number and stent geometry. In pulsatile flow, the minimum drug concentration in the zone of inter-wire spacing occurs at the maximum acceleration of the inlet flow while the maximum drug concentration gains at the maximum deceleration of the inlet flow. These results provide an understanding of the flow physics in the vicinity of drug-eluting stents and suggest strategies for optimal performance of drug-eluting stent to minimize flow disturbance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.21-28
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• 2007

The use of drug-eluting stents has dramatically reduced the incidence of restenosis however, much remains to be teamed about the performance of these stouts. In the present study, we tested the hypothesis that the design of drug-eluting stents influences the efficacy of local drug delivery to the arterial wall and that this effect depends on both arterial geometry and the prevailing flow conditions. We performed computational simulations in which the coupled Navier-Stokes and advection-diffusion equations were solved to determine the flow field and drug concentration in the vicinity of model drug-eluting stouts It is found that the characteristics of flow phenomena can be influenced greatly by the ratio of stent diameter to vessel diameter. The presence of drug-eluting stent may have profound effect on wall shear stresses, recirculation sizes and drug distributions. The results show that recirculation zone is influenced by the imposed flow conditions and stent diameter. In pulsatile flow, the low wall shear stress and high drug concentration occur along the arterial wall during the decelerating flow conditions. These results could provide the guideline for future drug-eluting stent designs toward reducing restenosis by affecting local wall shear stress distributions associated with neointimal hyperplasia.

• Journal of Biomedical Engineering Research
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• v.34 no.2
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• pp.69-72
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• 2013

The goal of this study is to develop test method for evaluating the drug eluting properties of drug eluting stents (DES). PBS and the detergent solutions, presented by each DES manufacturer, were used for drug release of DES coated with paclitaxel, zotarolimus and everolimus. The drugs which are coating DES were not released by PBS but released by the detergent solutions, finally paclitaxel 83.38%, zotarolimus 103.85% and everolimus 115.78%. It seems that the use of the detergents is necessary in order to release the drugs because those drugs are extremely hydrophobic. In conclusion, using of detergent solutions presented by each manufacturer were suitable for evaluating the drug eluting property of drug eluting stent.

• 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.

• Korean Journal of Clinical Pharmacy
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• v.22 no.2
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• pp.113-122
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• 2012

ACC/AHA/SCAI Guideline recommends for administration dual antiplatelet therapy after drug-eluting stent (DES) to prevent restenosis and stent thrombosis in patients with percutaneous coronary intervention (PCI). Recently triple antiplatelet therapy including cilostazol is known to reduce restenosis and stent thrombosis significantly after DES implantation. However, there is lack of data providing the efficacy of triple antiplatelet therapy. The purpose of this study is to evaluate the clinical effects of the triple therapy after DES implantation compared with the dual therapy. This retrospective study collected data from medical charts of 251 patients who received DES implantation between Jul 2006 and Jun 2008. They received either dual antiplatelet therapy (N = 154 clopidogrel and aspirin; Dual group) or triple antiplatelet therapy (N = 97 cliostazol, clopidogrel and aspirin; Triple group). Major adverse cardiac event rates (MACE, included total death, myocardial infarction, target lesion revascularization) at 12 months, 24 months, stent thrombosis, rates of bleeding complications and adverse drug reactions were compared between these two groups. Compared with the dual group, the triple group had a similar incidence of the MACE rates at 24months (12.3% vs. 12.4%, p = 0.99). There is no difference in overall stent thrombosis between two groups (Dual group 2.6% vs. Triple group 4.1%, p = 0.5). Subgroup analysis showed that diabetic patients got more benefit in reducing MACE rates but, there is no statistical difference. Bleeding complications and adverse drug effects were not different significantly. As compared with dual antiplatelet therapy, triple antiplatelet therapy did not reduce the 12-months, 24-months MACE rates and stent thrombosis. Bleeding complications and adverse drug effects were not different.

• Biomaterials and Biomechanics in Bioengineering
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• v.1 no.3
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• pp.131-150
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• 2014

Vascular stenting has a great attention as a treatment for coronary arteries diseases as compared with percutaneous balloon angioplasty. In-stent restenosis and thrombosis are side effects resulting from using bare metal stent (BMS). Employing platelet therapy allowed to reduce the rate of thrombosis, however, the rate of restenosis remains a major problem. In 2002, drug-eluting stents (DESs) were introduced as an effort to reduce the restenosis. The commercially available DESs continue to suffer from coating defects that might lead to a series of adverse effects. Most importantly, multiple concerns remain regarding the polymer coating integrity on metal surfaces or the relation of polymer irregularities to longterm adverse events.

• Biomaterials and Biomechanics in Bioengineering
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• v.1 no.1
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• pp.13-25
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• 2014

In the current study, a drug-eluting stent coated with biodegradable polymers and sirolimus was developed by using an ultrasonic nanocoater and characterized in aspects of surface smoothness and coating thickness. In addition, in vitro release profiles of sirolimus by changing top coating layer with different biodegradable polymers were investigated. Smooth surfaces with variable thickness could be fabricated by optimizing polymer concentration, flow rate, nozzle-tip distance, gas pressure, various solvents and ultrasonic power. Smooth surface could be generated by using volatile solvents (acetone, chloroform, and methylene chloride) or post-treating with solvent vapor. Coating thickness could be controlled by varying injection volume or polymer concentration, and higher concentration could reduce the coating time while obtaining the same thickness. The thickness measurement was the most effectively performed by a conventional cutting method among three different methods that were investigated in this study. Release profiles of sirolimus were effectively controlled by changing polymers for top layer. PLGA made the release rate 3 times faster than PDLLA and PLLA and all top layers prevented burst release at the initial phase of profiles. Our results will provide useful and informative knowledge for developing drug-eluting stents, especially coated with biodegradable polymers.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1455-1456
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• 2011

• Journal of Biomedical Engineering Research
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• v.34 no.3
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• pp.111-116
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• 2013

Finite element analysis(FEA) has been extensively applied in the analyses of biomechanical properties of stents. Geometrically, a closed-cell stent is an assembly of a number of repeated unit cells and exhibits periodicity in both longitudinal and circumferential directions. This study concentrates on various parameters of the FEA models for the analysis of drug-eluting biodegradable polymeric stents for application to the treatment of coronary artery disease. In order to determine the mechanical characteristics of biodegradable polymeric stents, FEA was used to model two different types of stents: tubular stents(TS) and helicoidal stents(HS). For this modeling, epigallocatechin-3-O-gallate (EGCG)-eluting poly[(L-lactide-co-${\varepsilon}$-caprolactone), PLCL] (E-PLCL) was chosen as drug-eluting stent materials. E-PLCL was prepared by blending PLCL with 5% EGCG as previously described. In addition, the effects of EGCG blending on the mechanical properties of PLCL were investigated for both types of stent models. EGCG did not affect tensile strength at break, but significantly increased elastic modulus of PLCL. It is suggested that FEA is a cost-effective method to improve the design of drug-eluting biodegradable polymeric stents.

• Polymer(Korea)
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• v.35 no.5
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• pp.483-487
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• 2011

For the preparation of effective non-vascular drug eluting stent (DES), pullulan acetate (PA) was investigated as a coating material for polytetrafluorethylene (PTFE)-covered stent. PA was coated on PTFE-covered stent (PTFE-stent) by dip coating technique, and then its surface morphology, drug release behavior and cellular toxicity were tested. Field emission-scanning electron microscopy (FE-SEM) result indicated that its surface was smoother after PA coating without any cracking. The sustained release behavior of paclitaxel from PA-coated PTFE membrane was observed for 80 days. Also, the biological stability of paclitaxel in the membrane was confirmed by annexin V binding assays. Furthermore, the antitumor activity was demonstrated by an in vivo test against CT-26 murine colorectal tumors. From the results, we concluded that PA was expected as a useful coating material to design an effective non-vascular DES.