• Journal of Biomedical Engineering Research
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• v.19 no.3
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• pp.297-303
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• 1998

The sinus distal to the prosthetic heart valve influences the valve closure behavior and velocity field near the valve, therefore affects the hydrodynamic performance of the prosthetic heart valve. In order to study the effects of valve distal geometry on the hydrodynamic performance of the prosthetic valves, mechanical bileaflet valve(SJMV), monoleaflet polymer valve(MLPV) and trileaflet polymer valve(FTPV) are inserted in the test sections which have the straight and the sinus shape distal to the valve. Leakage volumes and systolic mean pressure drops are measured in the pulsatile mock circulation flow loop. Leakage volumes are slightly less and systolic mean pressure drops are higher in the sinus test section comparing to those in the straight test section, but the differences are statistically insignificant. Flow waveforms are analyzed in order to predict the valve closure behavior. The distal sinus does not affect the closure of the MLPV, but early valve closure of SJMV is observed in the sinus test section. This effect is more significant in FTPV, and the reverse flow peak of FTPV is reduced in the sinus test section. Therefore the sinus distal to the valve can reduce the reverse flow jet caused by sudden valve closure.

• Macromolecular Research
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• v.14 no.5
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• pp.552-558
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• 2006

Biodegradable nanofibrous poly(L-lactic acid) (PLLA) scaffold was prepared by an electrospinning process for use in tissue regeneration. The nanofiber scaffold was treated with oxygen plasma and then simultaneously in situ grafted with hydrophilic acrylic acid (AA) to obtain PLLA-g-PAA. The fiber diameter, pore size, and porosity of the electrospun nanofibrous PLLA scaffold were estimated as $250\sim750nm,\;\sim30{\mu}m$, and 95%, respectively. The ultimate tensile strength was 1.7 MPa and the percent elongation at break was 120%. Although the physical and mechanical properties of the PLLA-g-PAA scaffold were comparable to those of the PLLA control, a significantly lower contact angle and significantly higher ratio of oxygen to carbon were notable on the PLLA-g-PAA surface. After the fibroblasts were cultured for up to 6 days, cell adhesion and proliferation were much improved on the nanofibrous PLLA-g-PAA scaffold than on either PLLA film or unmodified nanofibrous PLLA scaffold. The present work demonstrated that the applications of plasma treatment and hydrophilic AA grafting were effective to modify the surface of electrospun nanofibrous polymer scaffolds and that the altered surface characteristics significantly improved cell adhesion and proliferation.

• YAKHAK HOEJI
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• v.55 no.1
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• pp.69-74
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• 2011

Hyaluronic acid (HA) is a natural polymer consisting of disaccharide units of D-glucuronic acid and N-acetyl-D-glucosamine. It has a great potential and success in cosmetic and biomedical applications. However, native HA is highly soluble and easily metabolized by enzymes such as hyaluronidase. Thus, various studies have been reported on modifying the physicochemical properties of HA, while maintaining its biocompatibility. For controlled drug delivery, many trials for fabricating HA microspheres were achieved under chemical reaction. The HA microspheres fabricated to improve the physical stability of HA using adipic acid dihydrazide (ADH) by cross-linking reaction has been reported earlier, however it lacks the desired physical stability and rapidly decomposes by swelling or enzymes. Therefore, we prepared double cross-linked HA microspheres (DC-HA microspheres) and alginate containing HA microspheres (AC-HA microspheres) to enhance its physicochemical properties. DC-HA microspheres were prepared using trisodium trimetaphosphate (STMP) under crosslinking reaction after ADH cross-linking reaction. AC-HA microspheres were prepared by adding alginate as a networking polymer. These microspheres were characterized by morphology, particle size, zeta potential, stability against hyaluronidase. Results showed that the DC-HA and AC-HA microspheres are more stable than that of HA microspheres.

• Macromolecular Research
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• v.16 no.1
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• pp.15-20
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• 2008

The enhanced permeability and retention (EPR) effect is used extensively for the passive targeting of many macromolecular drugs for tumors. Indeed, the EPR concept has been a gold standard in polymeric anticancer drug delivery systems. This study investigated the tumoral distribution of self-assembled nanoparticles based on the EPR effect using fluorescein and radio-labeled nanoparticles. Self-assembled nanoparticles were prepared from amphiphilic chitosan derivatives, and their tissue distribution was examined in tumor-bearing mice. The size of the nanoparticles was controlled to be 330 run, which is a size suited for opening between the defective endothelial cells in tumors. The long-circulating polymer nanoparticles were allowed to gradually accumulate in the tumors for 11 days. The amount of nanoparticles accumulated in the tumors was remarkably augmented from 3.4%ID/g tissue at 1 day to 25.9%ID/g tissue at 11 days after i.v. administration. The self-assembled nanoparticles were sustained at a high level throughout the 14 day experimental period, indicating their long systemic retention in the blood circulation. The ${\gamma}$-images provided clear evidence of selective tumor localization of the $^{131}I$-labeled nanoparticles. Confocal microscopy revealed the fluorescein-labeled nanoparticles to be preferentially localized in the perivascular regions, suggesting their extravasation to the tumors through the hyperpermeable angiogenic tumor vasculature. This highly selective tumoral accumulation of nanoparticles was attributed to the leakiness of the blood vessels in the tumors and their long residence time in the blood circulation.

• Polymer(Korea)
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• v.37 no.4
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• pp.437-441
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• 2013

A novel sulfonate flame retardant, 1,3,5,7-tetrakis(phenyl-4-sodium sulfonate)adamantane (FR-A), was successfully synthesized from 1-bromoadamantane in sequential four-step reactions involving Fiedel-Crafts phenylation, sulphonation, hydrolysis, and neutralization. The success of synthesis was confirmed by FTIR spectra, $^1H$ NMR spectra, elemental analyses and mass spectra. The effect of FR-A on the flame retardacy of polycarbonate (PC) has been studied. Limiting oxygen index (LOI) and thermogravimetric analysis (TGA) showed that this novel sulfonate flame retardant had effective flame retardancy on polycarbonate (PC). With a small amount (0.08 wt%) of FR-A, the flame retardancy of PC was improved obviously, which got to UL 94 V-0 rating. TGA and DTA curves demonstrated that the additive raised the degradation rate of PC by promoting the quick formation of an insulating carbon layer on the surface, and confirmed that the flame retardant mechanism of PC/FR-A system was similar to potassium diphenylsulfone sulfonate (KSS).

• Polymer(Korea)
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• v.31 no.2
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• pp.153-159
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• 2007

Biodegradable molecularly imprinted polymers (MIPs) can be applied in the biomedical area of biosensors, drug delivery, etc. Therefore, in this study, biodegradable theophylline MIPs were synthesized via photopolymerization using a poly $(\varepsilon-caprolactone)$ (PCL) macromer as a cross-linker and their physical properties were investigated. The yield for the synthesis of the PCL macromer with terminal acrylate groups was ca. 78 mol%. The products were characterized by the combination of FT-IR and $^1H-NMR$ spectroscopic analyses. UV/Visible spectroscopic analysis for removing and rebinding theophylline was performed by monitoring the theophylline concentration in the solution. In vitro biodegradation tests of the theophylline MIPs performed in phosphate buffered saline (PBS) solution at $37^{\circ}C$ showed good biodegradability of the MIPs.

• Polymer(Korea)
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• v.37 no.6
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• pp.717-721
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• 2013

Biomaterials like silk fibroin (SF) and poly(vinyl alcohol) (PVA) have received increasing attention in biomedical applications because of their attractive properties such as hydrophobicity and biocompatibility. In this study, efficient systems consisting of interpenetrating SF/PVA hydrogels were prepared as potential candidate for wound dressing applications. A simple approach consisting of sonication and a freezing-thawing technique was adopted to fabricate the hydrogels. Different blend ratios consisting of SF (100, 75, 50, 25 and 0%) with respect to the weight of PVA were prepared. The produced hydrogels were characterized for physico-chemical investigations using various states of techniques like; FE-SEM, TGA, FTIR and tensile strength. The addition of PVA to SF was proved to be beneficial in terms of reducing the pore size and swelling ratio of hydrogels. The mechanical property of SF had been increased by addition of PVA. These results show that SF/PVA hydrogels may serve as potential candidates for wound dressing application.

• Polymer(Korea)
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• v.37 no.6
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• pp.802-808
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• 2013

The purpose of this study was to develop an aloin-loaded wound dressing with an enhanced healing effect. The cross-linked hydrogel films were prepared with poly(vinyl alcohol) (PVA) and carboxyl methyl cellulose (CMC) using a freeze-thawing (F-T) method. Their gel properties, release of drug, in vivo wound healing effect and histopathology were then evaluated. In the wound healing test, this aloin loaded PVA/CMC hydrogel showed faster healing of the wound made in rat dorsum than the aloin carbomer 934 gel or the control (carbomer 934 gel) due to phytochemical activity of aloin and moisture of CMC. In conclusion, the aloin-loaded wound dressing composed of 5% PVA, 5% CMC and 0.125% aloin is a potential wound dressing with enhanced wound healing effect.

• Polymer(Korea)
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• v.32 no.5
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• pp.409-414
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• 2008

The fabrication of gelatin nanofibers by electro spinning has been examined using the TFE/DW co-solvent system. It has been found that no beads-on-string structure was formed for the solution containing ionic salts. The resulting fibers exhibited a uniform diameter ranging from 110 to 125 nm. As the concentration of ionic salts increases, the beads become smaller and more spindle like, due to the increase of viscosity and conductivity. The addition of ionic salts induces a higher charge density on the surface of ejected jet during spinning, leading that higher elongation forces are applied to the jet. The higher enhancement of viscosity and conductivity was observed in gelatin solutions by the use of divalent salt. However, the concentration of ionic salts scarcely affected the variation of fiber diameter. While very low crystallinity was observed from XRD pattern for the sample containing no ionic salt, which increased with increasing the concentration of ionic salts.

• The Korean Journal of Vision Science
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• v.20 no.4
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• pp.513-521
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• 2018

Purpose : : In this study, we made dopamine-functionalized hydrogels containing a cross-linked hyaluronic acid (HA) network and investigated their antioxidant activities. Methods : In the first step, we made poly hydroxyethyl methacrylate(p(HEMA))-based hydrogels post-modified with an interpenetrating polymer network(IPN) structure composed of HA polymers and a p(HEMA) network. The subsequent functionalization with dopamine via an amide coupling reaction resulted in the antioxidant hydrogels. Their antioxidant activities were evaluated using 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl radical scavenging assays. Results : The dopamine-modified hydrogels exhibited significant antioxidant activities, when compared to unmodified control. The presence of the HA-IPN structure improved the surface wettability of the hydrogel while dopamine-conjugated IPN hydrogel did not demonstrate the significant difference compared to hydrogel control. Dopamine-modified hydrogels exhibited high transmittance (>88%). Conclusion : The results demonstrate that the development of antioxidant hydrogels based on dopamine-conjugated HA-IPN structures may help develop ophthalmic and biomedical materials.