• 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.

• 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.

• Polymer(Korea)
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• v.35 no.3
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• pp.260-264
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• 2011

Biodegradable polymeric stents have been issued to replace the existing non-degradable metal stents due to relatively improved biocompatibility and low side effects. Fundamentally, all the stents must possess the desired mechanism strength, especially, compression or radial force to maintain the diameters of expanded vessels. Therefore, this study suggests a helical structure and focused on the relation between the lateral compression and structural factors, Unlike a cylindrical model, the radial force of the helical model is proportional to the thickness and the length to the power of one, whereas the diameter to the power of 1.6. The function obtained from these results might provide the fundamental information to design and prepare the stem for clinical applications.

• Polymer(Korea)
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• v.34 no.2
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• pp.172-177
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• 2010

Although many researchers have studied the efficacy of paclitaxel (PTX) on many cells during the last two decades, little work has been reported on the importance of release kinetics inhibiting cell proliferation. The aim of this study is to examine the release behavior of the PTX on various biodegradable polymers such as poly(lactic-co-glycolic acid)(PLGA), poly-L-lactide (PLLA), and polycaprolactone (PCL) for drug-eluting stents (DES). The PTX from the fabricated films was released for 8 weeks and the degree of degradation of the films was observed by FE-SEM. Although the degradation time of PCL was the slowest, the PTX release rate was the fastest among them and followed by PLGA and PLLA with the equivalent PTX concentration. It suggests that hydrophobic drug such as PTX from polymer with low $T_g$ like PCL could be moved easily and released rapidly in body temperature.

• Polymer(Korea)
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• v.34 no.2
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• pp.178-183
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• 2010

Medical metal stents inserted to patients with a cardiovascular disease associated with coronary artery system have relatively increased the survival rate. The development of new stents is, however, urgently required due to restenosis and late thrombosis generated in metal stents. To solve these problems, the biodegradable polymers such as poly(lactide-co-glycolide) (PLGA), poly(L-lactide)(PLLA), and poly ($\varepsilon$-caprolactone)(PCL) were mixed with alpha lipoic acid (ALA), which is well known to inhibit the proliferation of neointimal hyperplasia. Subsequently, the ALA-loaded polymers were coated on stainless steel by electrospray. The drug-eluting behaviors from the coated polymers were investigated according to kinds and concentrations of polymers, spray rates, and kinds of solvents. The drug-eluting rate from PCL with the lowest glass transition temperature was the fastest among three polymers and followed by PLGA and PLLA. The surface roughness increased as the spray rate was increased and also the drug-eluting rate was affected by kinds of solvents with different boiling point. It is expected that drug-eluting stent (DES) coated with ALA-loaded polymers can be applied practically for clinical applications by controlling the behavior of drug release.

• Journal of Korean Neurosurgical Society
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• v.64 no.6
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• pp.853-863
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• 2021

Objective : Biodegradable poly-L-lactic acid (PLLA) with a highly biocompatible surface via tantalum (Ta) ion implantation can be an innovative solution for the problems associated with current biodegradable stents. The purpose of this study is to develop a Taimplanted PLLA stent for clinical use and to investigate its biological performance capabilities. Methods : A series of in vitro and in vivo tests were used to assess the biological performance of bare and Ta-implanted PLLA stents. The re-endothelialization ability and thrombogenicity were examined through in vitro endothelial cell and platelet adhesion tests. An in vivo swine model was used to evaluate the effects of Ta ion implantation on subacute restenosis and thrombosis. Angiographic and histologic evaluations were conducted at one, two and three months post-treatment. Results : The Ta-implanted PLLA stent was successfully fabricated, exhibiting a smooth surface morphology and modified layer integration. After Ta ion implantation, the surface properties were more favorable for rapid endothelialization and for less platelet attachment compared to the bare PLLA stent. In an in vivo animal test, follow-up angiography showed no evidence of in-stent stenosis in either group. In a microscopic histologic examination, luminal thrombus formation was significantly suppressed in the Ta-implanted PLLA stent group according to the 2-month follow-up assessment (21.2% vs. 63.9%, p=0.005). Cells positive for CD 68, a marker for the monocyte lineage, were less frequently identified around the Ta-implanted PLLA stent in the 1-month follow-up assessments. Conclusion : The use of a Ta-implanted PLLA stent appears to promote re-endothelialization and anti-thrombogenicity.

• 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.

• Polymer(Korea)
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• v.33 no.6
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• pp.620-624
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• 2009

Biomedical metal implants have been used clinically for replacement, restoration, or improvement of injury bodies based on high mechanical properties, but it has some risks such as the inflammatory, late thrombosis, or restenosis due to the low biocompatibility and toxicity. In various techniques of surface treatment developed to preserve these drawbacks, this study examined the electrospray coating technology with biodegradable poly (lactic-co-glycoic acid) (PLGA) on metal surface. Based on fundamental examination of electrospraying and solution parameters, the surface morphology of coated film was closely related to the boiling point of solvent, in-flight distance, and droplet size. The thickness of polymer film was linearly proportional to the emerged volume. This result exhibits that the polymeric droplets were continuously deposited on the polymer film. Therefore, the electrospray coating technology might be applied into the fabrication of single/multi-layered polymer film in nano-/micro-thickness and the control of the topology for biomedical metal implants including stents.

• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.396-406
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• 2018

In this study, a polydioxanone (PDO) and poly(L-lactic acid) (PLLA) sheath-core biphasic monofilament was designed to develop an esophageal stent with improved mechanical properties and controlled biodegradability. The radial force of PDO/PLLA sheath-core stent was 10.24 N, while that of PDO stent was 5.64 N. Deteriorations of tensile strength, elastic modulus and elongation during degradation test were also delayed on PDO/PLLA group. Hyaluronic acid-dopamine conjugate and $BaSO_4/PDO$ conjugate coating layers provided improved tissue adhesion strength and reasonable X-ray contrast, respectively. Taken all together, the sheath-core filaments with tissue adhesive and radiopaque properties will be useful in designing esophageal stents.

• Korean Circulation Journal
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• v.54 no.6
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• pp.339-350
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• 2024

Background and Objectives: Ultimaster^TM, a third-generation sirolimus-eluting stent using biodegradable polymer, has been introduced to overcome long term adverse vascular events, such as restenosis or stent thrombosis. In the present study, we aimed to evaluate the 12-month clinical outcomes of Ultimaster^TM stents in Korean patients with coronary artery disease. Methods: This study is a multicenter, prospective, observational registry across 12 hospitals. To reflect real-world clinical evidence, non-selective subtypes of patients and lesions were included in this study. The study end point was target lesion failure (TLF) (the composite of cardiac death, target vessel myocardial infarction [MI], and target lesion revascularization [TLR]) at 12-month clinical follow up. Results: A total of 576 patients were enrolled between November 2016 and May 2021. Most of the patients were male (76.5%), with a mean age of 66.0±11.2 years. Among the included patients, 40.1% had diabetes mellitus (DM) and 67.9% had acute coronary syndrome (ACS). At 12 months, the incidence of TLF was 4.1%. The incidence of cardiac death was 1.5%, MI was 1.0%, TLR was 2.7%, and stent thrombosis was 0.6%. In subgroup analysis based on the presence of ACS, DM, hypertension, dyslipidemia, or bifurcation, there were no major differences in the incidence of the primary endpoint. Conclusions: The present registry shows that Ultimaster^TM stent is safe and effective for routine real-world clinical practice in non-selective Korean patients, having a low rate of adverse events at least up to 12 months.