• Polymer(Korea)
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• v.32 no.3
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• pp.219-229
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• 2008

A pH sensitive ternary copolymer gel was synthesized in the presence of ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent through radical polymerization of vinyl acetate (VA), acrylic acid (AA) and methyl acrylate(MA) with a weight ratio of 1 : 1.3 : 1. A number of experiments were carried out to determine the swelling behavior of the gel under a variety of pH conditions of the swelling medium. As the pH of the swelling medium was changed from 1.0 to 8.0 at $37^{\circ}C$, the gel showed a shift in the pH-dependent swelling behavior from Fickian (n=0.3447) to non-Fickian (n=0.9125). The resulting swelling parameters were analyzed using graphical and statistical methods. The results showed that the swelling of the gel was controlled by the pH of the medium, i.e. $n=n_o{\exp}(S_{C}pH)$, where n is the diffusion exponent, $n_o(=28.9645{\times}10^{-2})$ is the pre-exponential factor and $S_C$(=0.1417) is pH sensitivity coefficient. The swelling behavior of the gel was also examined in aliphatic alcohols. The results showed that the rate of swelling increased with increasing number of carbon atoms in the alcoholic molecular chain.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1935-1937
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• 2003

최근 콜레스테롤 센서는 전극 상에 효소를 고정화 하는 방식을 이용하여 센서의 집적도를 높이는 시도가 이루어지고 있다. 이러한 전극 상의 효소고정화 방식으로 entrapment, cross liking, covalently binding 등이 있다. 본 논문에서는 이러한 효소 고정화 방식-전도성 고분자인 P3MT를 사용하여 entrap시키는 방법과 silanization을 이용한 covalent bonding 시키는 방법-에 따른 전기화학 센서의 감도 특성에 관한 연구를 수행하였다. 전도성 고분자를 사용한 고정화 방법은 cyclic voltammograms으로 scan rate 10 mA/s, potential 0.5-1.3V의 조건하에서 P3MT를 Polymerization하고, 효소 고정화를 위해 chromoampermeter로 potential 0.6V에서 900초 동안 수행하였다. silanization을 이용한 covalent bonding 시키는 방법은 nitric acid로 Pt 전극표면을 산화시키고, APTER로 silanization 공정을 시행하였다. 효소 고정화를 위해 전해질로는 0.1M Phosphate buffer solution을 사용하여 cyclic voltammograms으로 scan rate 50 mA/s 전위 0.0-0.7V의 조건 하에서 수행하였다. 이 결과 전도성 고분자를 이용한 고정화 방법에서의 senstivity가 0.89 ${\mu}A/mM{\cdot}cm^2$이고, silanization을 이용한 효소 고정화 방법에서는 1.51 ${\mu}A/mM{\cdot}cm^2$였다. 이처럼 후자의 방법에서 더 좋은 감도 특성이 나타났다. 따라서, silanization을 이용한 고정화 방법이 센서 제작 방식으로 더 적합하다고 사료된다.

• Journal of Pharmaceutical Investigation
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• v.34 no.4
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• pp.275-281
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• 2004

We have studied the effect of polarity, current density, current duration, crosslinking density, swelling ratio, and permeation enhancers on the transdermal flux of ketoprofen from acrylamide hydrogel. Hydrogel was prepared by free radical crosslinking polymerization of acrylamide. Drug loading was made just before transport experiment by soaking the hydrogel in solution containing drug. In vitro flux study using hairless mouse skin was performed at $36.5^{\circ}C$ using side-by-side diffusion cell, and the drug was analysed using HPLC/UV system. The result showed that, compared to passive flux, the total amount of drug transported increased about 18 folds by the application of $0.4\;mA/cm^2$ cathodal current. Anodal delivery with same current density also increased the total amount of drug transported about 13 folds. It seemed that the increase in flux was due to the electrorepulsion and the increase in passive permeability of the skin by the current application. Flux increased as current density, the duration of current application and loading amount (swelling duration) increased. As the cross linking density of the hydrogel increased, flux clearly decreased. The effect of hydrophilic enhancers (urea, N-methyl pyrrolidone, Tween 20) and some hydrophobic enhancers (propylene glycol monolaurate and isopropyl myristate) was minimal. However, about 3 folds increase in flux was observed when 5% oleic acid was used. Overall, these results provide some useful information on the design of an optimized iontophoretic delivery system of ketoprofen.

• Journal of the Korean Chemical Society
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• v.65 no.5
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• pp.320-326
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• 2021

This study investigated the effect of the structure of the crosslinking agent used in contact lens polymerization on the physical properties and drug dissolution of contact lenses.es Contact lenses were manufactured using 0.3% and 3% of 4 types of crosslinking agents, respectively, and ofloxacin was used as the drug. Contact lenses using hydrophilic crosslinking agents improved water contents and wettability, and the more hydrophilic functional groups, the greater the effect. Contact lenses with a high concentration of crosslinking agent had a low concentration of eluted drug and a longer release time. The cross-linking agent structure of contact lenses had an effect on improving the performance of contact lenses and controlling drug release.

• Elastomers and Composites
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• v.57 no.3
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• pp.100-106
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• 2022

Waterborne polyurethane-acrylate(WPUA) dispersions were prepared by surfactant-free emulsion polymerization in a two-step process. In the first step, polytetrahydrofuran, isophorone diisocyanate, dimethylol proponic acid, and 2-hydroxyethyl methacrylate were used to synthesize a vinyl-terminated polyurethane prepolymer. In the second step, styrene, methyl methacrylate, butyl acrylate, and different multi-functional crosslinkers were copolymerized. 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, and pentaerythritol tetraacrylate were used as the crosslinkers, and their effect on the mechanical and thermal properties of WPUA was investigated. Overall, as the number of functional groups of the cross-linker increased, the gel fraction improved to 79.26%, the particle size increased from 75.9 nm to 148.7 nm, and the tensile strength was improved from 5.86 MPa to 12.40 MPa. In thermal properties, the glass transition temperature and decomposition temperature increased by 9.9℃ and 18℃, respectively. The chemical structures of the WPUA dispersions were characterized by Fourier-transform infrared spectroscopy. The synthesized WPUA has high potential for applications such as coatings, leather coatings, adhesives, and wood finishing.

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.586-592
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• 2017

In this study, acrylic resins with solids content of 75% were prepared by addition polymerization of n-butyl acrylate (BA), methyl methacrylate (MMA), 2-hydroxypropyl methacrylate (HPMA) and acetoacetoxyethyl methacrylate (AAEM) monomers. At this time, the glass transition temperature ($T_g$) of the acrylic resin was changed to 20, 30 and $40^{\circ}C$, and the hydroxyl value (OH value) was changed to 60, 90 and 120. As a result, the viscosity of acrylic resin increased with increasing $T_g$ and hydroxyl (OH) value. The synthesized acrylic resin was designed to have a high cross-link density to maintain high elasticity and high durability. The crosslinked acrylic resin was used to prepare an acrylic urethane clear coating by curing reaction with a block isocyanate (Desmodur BL-3175). The physical properties of the clear paints were analyzed by measuring viscosity, adhesion, pencil hardness and $60^{\circ}$ specular gloss. Acrylic urethane clear coatings were prepared as specimens and evaluated for various properties to be applied as top coatings for coil coating. The prepared coatings were excellent in adhesion, excellent in $60^{\circ}$ specular gloss and pencil hardness, and eco-friendly.

• BMB Reports
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• v.40 no.2
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• pp.218-225
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• 2007

In Arabidopsis thaliana, the microtubule-associated protein AtMAP65-1 shows various functions on microtubule dynamics and organizations. However, it is still an open question about whether AtMAP65-1 binds to tubulin dimers and how it regulates microtubule dynamics. In present study, the tubulin-binding activity of AtMAP65-1 was investigated. Pull-down and co-sedimentation exp eriments demonstrated that AtMAP65-1 bound to tubulin dimers,at a molar ratio of 1 : 1. Cross-linking experiments showed that AtMAP65-1 bound to tubulin dimers by interacting with $\alpha$-tubulin of the tubulin heterodimer. Interfering the bundling effect of AtMAP65-1 by addition of salt and monitoring the tubulin assembly, the experiment results indicated that AtMAP65-1 promoted tubulin assembly by interacting with tubulin dimers. In addition, five truncated versions of AtMAP65-1, namely AtMAP65-1 $\Delta$N339 (amino acids 340-587); AtMAP65-1 $\Delta$N494 (amino acids 495-587); AtMAP65-1 340-494 (amino acids 340-494); AtMAP65-1 $\Delta$C495 (amino acids 1-494) and AtMAP65-1 $\Delta$C340 (amino acids 1-339), were tested for their binding activities and roles in tubulin polymerization in vitro. Four (AtMAP65-1 $\Delta$N339, $\Delta$N494, AtMAP65-1 340-494 and $\Delta$C495) from the five truncated proteins were able to co-sediment with microtubules, and three (AtMAP65-1 $\Delta$N339, $\Delta$N494 and AtMAP65-1 340-494) of them could bind to tubulin dimers in vitro. Among the three truncated proteins, AtMAP65-1 $\Delta$N339 showed the greatest activity to promote tubulin polymerization, AtMAP65-1 $\Delta$N494 exhibited almost the same activity as the full length protein in promoting tubulin assembly, and AtMAP65-1 340-494 had minor activity to promote tubulin assembly. On the contrast, AtMAP65-1 $\Delta$C495, which bound to microtubules but not to tubulin dimers, did not affect tubulin assembly. Our study suggested that AtMAP65-1 might promote tubulin assembly by binding to tubulin dimers in vivo.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.2
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• pp.245-253
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• 2003

The degree of conversion of cross-linked polymer has great importance in determining the physical and mechanical properties, and biocompatibility. Therefore, this study examined the comparison of light-cured composite resin polymerization of various light-curing systems composed of plasma arc, halogen, LED curing units and pluse-delay curing with FTIR. From this experiment, The following results were obtained : 1. From FTIR, the degree of conversion(DC) of composite resin was 34.52-49.31%, DC of composite resin used in Flipo was $39.36{\pm}1.22%$, CrediII $45.64{\pm}1.34%$, XL3000 $43.48{\pm}1.34%$, VIP(mode 4) $44.31{\pm}0.72%$, LUXOMAX $49.31{\pm}2.37%$, Elipar Freelight $44.51{\pm}0.62%$ and $34.52{\pm}0.85%$ in pulse-delay curing. 2. The degree of conversion of composite resin in each light-curing unit was highest DC of the LUXOMAX system, lowest DC of the pulse-delay curing. 3. Compared with other curing system, Flipo, LUXOMAX, and pulse-delay curing were significant difference(p<0.05). 4. In same curing method group, the differences of each light-curing unit were no significace in halogen(conventional) curing method(p>0.05), but significance in plasma arc curing and LED curing method(p<0.05).

• The Korean Journal of Pharmacology
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• v.21 no.2
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• pp.79-89
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• 1985

Mechanism of calcium transport inhibition of cardiac sarcoplasmic reticulum (SR) by oxygen free radicals was examined. Effects of oxygen free radicals generated by xanthine/xanthine oxidase (X/XO) system on isolated porcine ventricle SR were studied with respect to its calcium binding, lipid peroxidation, SH-group content and alteration of membrane protein components. The results are as follows. 1) Calcium binding of isolated SR was markedly inhibited by X/XO. 2) During the incubation of sarcoplasmic reticulum with xanthine/xanthine oxidase, there were marked inclose in lipid peroxidation and reduction of SH-group content. 3) An antioxidant, p-phenylenediamine effectively prevented the lipid peroxidation but partially prevented the calcium binding inhibition of X/XO treated SR. 4) The reduction of SH-group content of SR treated with X/XO was partially prevented by p-phenylendiamine. 5) When modifying SH-group of SR by treatment with DTNB, the inhibition of calcium binding activity was partially prevented. 6) On gel-permeation chromatography of X/XO-treated sarcoplasmic reticulum, there was an increase of small molecular weight products, probably protein degradation products. 7) Semicarbazide, which prevents the cross-linking reaction of protein components, did not affect the calcium binding inhibition of X/XO-treated SR. From these results, it is suggested that the inhibition of calcium binding of SR by oxygen free radicals results from the consequence of multiple changes of SR components, which are lipid peroxidation, SH-group oxidation and degradation of protein components.

• Restorative Dentistry and Endodontics
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• v.33 no.5
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• pp.428-434
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• 2008

The purpose of this study was to compare the microtensile bond strength in Class I cavities associated with different light curing modes of same light energy density. Occlusal enamel was removed to expose a flat dentin surface and twenty box-shaped Class I cavities were prepared in dentin. Single Bond (3M Dental product) was applied and Z 250 was inserted using bulk technique. The composite was light-cured using one of four techniques, pulse delay (PD group), soft-start (SS group), pulse cure (PC group) and standard continuous cure (CC group). The light-curing unit capable of adjusting time and intensity (VIP, Bisco Dental product) was selected and the light energy density for all curing modes was fixed at $16J/cm^2$. After storage for 24 hours, specimens were sectioned into beams with a rectangular cross-sectional area of approximately $1mm^2$ Microtensile bond strength $({\mu}TBS)$ test was per- formed using a univel·sal testing machine (EZ Test, Shimadzu Co.). The results were analyzed using oneway ANOVA and Tukey's test at significance level 0.05. The ${\mu}TBS$ of PD group and SS group was higher than that of PC group and CC group. Within the limitations of this in vitro study, modification of curing modes such as pulse delay and soft start polymerization can improve resin/dentin bond strength in Class I cavities by controlling polymerization velocity of composite resin.