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ABSTRACT: We have developed hydrodynamic filtration method in microfluidic device for the efficient size-selection of polydisperse lipid vesicles for giant unilamellar vesicles (GUVs), in which vesicles were formed by electroformation method. Combining pinched flow channel design before hydrodynamic filtration, GUVs were flowed and guided to filtration channels, in which small lipid vesicles were further filtered and GUV were remained in main flow channels. For increasing the selectivity of GUV in outlets, length of slit section, or relative flow rate were controlled and drain channels were introduced for avoiding back flow. At higher flow rate in a pinched flow, the fraction of recovered GUVs (>10 microm) were increased, in which most of small vesicles were filtered.
Journal of Biomedical Nanotechnology 04/2013; 9(4):610-4. · 4.22 Impact Factor
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ABSTRACT: In this study, a facile route to fabricate micropatterns of cells is presented on the basis of electron irradiation of poly(dimethylsiloxane) (PDMS). PDMS films were irradiated with electron beams through a pattern mask with micrometer-sized grids. After irradiation, the changes in the chemical composition, morphology, and wettability of the PDMS surface were investigated by using an X-ray photoelectron spectrometer, an atomic force microscope, and a contact anglometer. The results of the surface analysis revealed that the hydrophobic PDMS surface was changed into a hydrophilic one by the electron irradiation. Furthermore, on the basis of cell culturing on the selectively-irradiated PDMS, cells such as NIH3T3 and L929 were selectively adhered to and proliferated on the irradiated regions of the PDMS surface, resulting in the micropatterns of the cells on the PDMS surface.
Journal of Biomedical Nanotechnology 03/2013; 9(3):461-6. · 4.22 Impact Factor
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ABSTRACT: Micropatterning of titanium dioxide (TiO2) on the surface of thin poly(dimethyl siloxane) (PDMS) films was described by means of proton irradiation and liquid-phase deposition (LPD) techniques. The surface of thin PDMS films was irradiated with accelerated proton ions through a pattern mask in the absence or presence of oxygen in order to create hydrophilically/hydrophobically patterned surfaces. The results of the surface analysis revealed that the PDMS films irradiated at the fluence of 1 x 10(15) ions cm-2 in the presence of oxygen showed the highest hydrophilicity. The LPD of TiO2 particles on the patterned PDMS film surface showed a selective deposition of TiO2 on the irradiated regions, leading to well defined TiO2 micropatterns. The crystal structure of the formed TiO2 films was found to be in an anatase phase by X-ray diffraction analysis. This process can be applied for patterning various metal and metal oxide particles on a polymer substrate.
Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4284-8. · 1.56 Impact Factor
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ABSTRACT: In this article, we reported the effects of the addition of various aliphatic diamines (ADAs) on the dynamic mechanical properties of poly(styrene-co-styrenesulfonic acid) copolymers. It was found that the ionic modulus decreased with increasing chain length of ADAs but increased for the ADA12-containing ionomers. Upon the neutralization of the copolymers with ADAs, a minor change in the size and position of the matrix loss tangent peak was observed. However, the position of the cluster loss tangent peaks shifted to lower temperatures, and the shift rate depended on the chain length of ADAs. Thus, it was suggested that the ADAs acted mainly as preferential plasticizer for the cluster regions. In addition, the effect of the amount of ADA on the difference between the matrix and cluster temperatures of the ionomers was strongest than that of the type of ADA or ion content. The X-ray peak of ADA12 suggested that the ADA12 acted both as plasticizer and as filler.
Journal of Applied Polymer Science 01/2012; · 1.29 Impact Factor
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ABSTRACT: The effect of shear on the electrical percolation network of carbon nanotube (CNT)-polymer composites is investigated using computer simulations. Configurations of CNTs in a simple shear, obtained by using Monte Carlo simulations, are used to locate the electrical percolation network of CNTs and calculate the electric conductivity. When exposed to the shear, CNTs align parallel to the shear direction and the electrical percolation threshold CNT concentration decreases. Meanwhile, after a certain period of the shear imposition above a critical shear rate, CNTs begin to form an aggregate and the percolating network of CNTs is broken, thus decreasing the electric conductivity significantly. We also construct quasiphase diagrams for the aggregate formation and the electrical percolation network formation to investigate the effect of the shear rate and CNT concentration.
Physical Review E 01/2012; 85(1 Pt 1):011143. · 2.26 Impact Factor
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ABSTRACT: Various properties of electrowetting such as reversibility, reproducibility and mobility have been investigated experimentally. A conductive water drop on a thin hydrophobic film of amorphous fluropolymers coated on the counter electrode showed unexpectedly the poor reversibility under the discontinuous voltage, so called the contact angle hysteresis. The hysteresis could not been completely suppressed by inserting additionally a thick parylene-C film which has the high dielectric constant and no pinholes. However, both the reversibility and the reproducibility have been enhanced under the continuous voltage starting from the highest absolute electric potential.
Journal of Nanoscience and Nanotechnology 08/2011; 11(8):7132-6. · 1.56 Impact Factor
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ABSTRACT: We used X-ray reflectivity to investigate the structures of phospholipid multilayers with transcription-activating-factor-derived peptide (TDP) as a function of the membrane charge density. Mixed phospholipid multilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl -sn-glycero-3-phosphoserine (DPPS) with different mixing ratios (C:S) were used to elucidate the various charge densities in a plasma membrane. We fixed the peptide/lipid molar ratio (P/L) and varied the DPPC/DPPS molar ratio in the mixed multilayer. In the pure DPPC multilayer, the incorporation of TDP had nearly no effect on the bilayer thickness of the mixed lipid multilayer. However, in the mixed DPPC/DPPS multilayer, the incorporation of TDP decreased the bilayer thickness, suggesting that the TDP peptide had a stronger interaction with DPPS than with DPPC and caused disorder in the lamellar structure. Combining this with the refined X-ray reflectivity (XR) data, we concluded that the TDP existed more in the headgroup region of the TDP-induced segregated DPPS in the mixed multilayer and caused significant membrane thinning.
Biointerphases 06/2011; 6(2):73-8. · 2.21 Impact Factor
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ABSTRACT: Migration of Au nanoparticles by thermal diffusion into porous SiO2 matrix substrates has been studied using secondary ion mass spectroscopy (SIMS). When the samples having four different porosities were annealed at T = 410 K for 1.5 h, no noticeable variations in the thermal diffusion of Au nanoparticles were observed. All the measured diffusion coefficients of Au particles, were an order of 10(-15) cm2/s at 300-410 K in a very limited interfacial region. Regardless of their porosities, the pores must be discontinuous, which acts as a diffusion barrier to block the continuous diffusion of Au particles.
Journal of Nanoscience and Nanotechnology 05/2011; 11(5):4400-5. · 1.56 Impact Factor
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ABSTRACT: Attachment and proliferation of NIH-3T3 fibroblast cells on random polymer surfaces, polystyrene sulfonated acid (PSSAx) with five different degrees of sulfonation (x = 0%, 5%, 10%, 15% and 33%) and on a tissue culture polystyrene (TCPS) surface were studied. The surface properties, wettability and roughness were measured by water-contact angle and atomic force microscopy measurement. The wettability and surface roughness increased with increasing the content of sulfonic acid groups on the surfaces. The number of cells attached on the surface after seeding increased with increasing x and reached to the maximum value on PSSA15. The cell proliferation also increased with increasing x. However, cell proliferation was slow down on PSSA33 in comparison to PSSA10 and PSSA15 surfaces after 48 h culture.
Journal of Nanoscience and Nanotechnology 05/2011; 11(5):4227-30. · 1.56 Impact Factor
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ABSTRACT: Patterned graft polymerization of a functional monomer on a hydrophobic polymer surface was proposed for biomolecule patterning. A poly(vinylidene fluoride) (PVDF) film surface was selectively activated by ion implantation through a pattern mask and acrylic acid (AA) was then graft polymerized onto the activated regions of the PVDF surfaces. The peroxide concentration on the implanted surface depended on the fluence, which had a considerable effect on the grafting degree of AA. Afterwards, amine-functionalized biotin and probe DNA were immobilized on the poly(acrylic acid)-grafted regions of the PVDF surfaces. Specific binding of biotin with streptavidin and hybridization of probe DNA with complimentary DNA proved successful protein and DNA patterning and well-defined 50 microm dot-type patterns of the streptavidin and DNA were obtained. These results confirmed the potential of this strategy for patterning of various biomolecules.
Journal of Nanoscience and Nanotechnology 05/2011; 11(5):4562-6. · 1.56 Impact Factor
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ABSTRACT: The structure and the percolation behavior of the composite of carbon nanotubes (CNTs), CNT molecular junctions and polymers are studied using Monte Carlo (MC) simulations. We model a CNT as a rigid rod composed of hard spheres. "X" and "Y" molecular junctions of CNTs are constructed by joining four and three segments of CNTs, respectively. The model system consists of CNTs mixed with either "X" or "Y" molecular junctions. The system is equilibrated using Monte Carlo simulations and the equilibrated configurations are used to locate the clusters of connected molecules via a recursive algorithm. The fraction (P(perc)) of configurations with a percolating cluster is then estimated for a given total volume fraction (phi(t)) of molecules. When P(perc) reaches 0.5, phi(t) of the system is considered a percolation threshold concentration (phi(c)). The percolation behavior is found to be sensitive to the aspect ratio of CNTs and the concentration and the shape of molecular junctions. phi(c) is decreased with an increase in the aspect ratio of CNTs. As the mole fraction of molecular junctions is increased, phi(c) is decreased significantly, which suggests that molecular junctions could enhance the electric conductivity of CNT-polymer composites. X junctions are found to construct a percolating network more effectively than Y junctions. More interestingly, even though molecular junctions change the percolation behavior significantly, the site-site pair correlation functions of CNTs hardly show any difference as the mole fraction of molecular junctions is increased. This implies that the percolation of CNTs is determined by the subtle many-body correlation of CNTs that is not captured by the site-site pair correlation functions.
Journal of Nanoscience and Nanotechnology 05/2011; 11(5):4317-23. · 1.56 Impact Factor
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ABSTRACT: The dynamic and living characteristics of monolayers at the air-water interface of a cyclohexapeptide (C6G) and a cyclooctapeptide (C8G), both composed of glutamic acid and 3-aminobenzoic acid subunits in an alternating sequence, were investigated using the Langmuir balance technique, Brewster angle microscopy (BAM), and X-ray reflectivity (XR). An alanine-containing cyclohexapeptide (C6A) was included in this study for comparison. All three cyclopeptides preferentially adopt an orientation parallel to the subphase at low surface pressure. Continuous compression then causes the molecules to flip to a perpendicular state, thus minimizing their molecular area. In contrast to C8G and C6A, a pronounced hysteresis observed during the compression-expansion cycle of C6G indicates that strong intermolecular interactions between the cyclopeptide rings occur in the monolayers of this peptide. This result is supported by BAM measurements that show the formation of crystallite structures for C6G at high surface pressures, whereas no structures were observed for C8G and C6A. These results indicate that C6G is able to self-assemble upon surface compression, an ability that is obviously critically dependent on the correct ring size and composition of the peptide. The presence of hydrogen bond acceptors in the side chains of C6G suggests that the structural stabilization of the monolayer is due to H-bonding, possibly between ring NH groups and side chain CO groups. Our in situ study thus provides a detailed understanding of the molecular dynamics and uninterrupted interfacial behavior of the three peptides in a real-time frame.
Israel Journal of Chemistry. 03/2010; 45(3):345 - 352.
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Jae-Hak Choi,
Mi-Young An,
Byoung-Min Lee,
Dong-Ki Kim,
Chan-Hee Jung,
In-Tae Hwang,
Jung-Soo Lee,
Young-Chang Nho, Kwanwoo Shin,
Kang-Moo Huh,
Sung-Kwon Hong
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ABSTRACT: This study describes a new patterning method of poly(vinyl pyrrolidone) (PVP) containing silver nanoparticles by using ion irradiation. The thin films prepared from PVP/silver nanoparticle solutions were irradiated through a mask with accelerated H+ ions. Well-defined 50 microm line (pitch 150 microm) patterns were generated from the film irradiated at 1 x 10(16) ions/cm2. The heat treatment effect on the morphology of the patterns was investigated by using a scanning electron microscope with an energy dispersive X-ray spectrometer. The results confirmed that the silver nanoparticles were successfully immobilized in the PVP patterns and the patterns were changed into silver particles by heat treatment above 300 degrees C.
Journal of Nanoscience and Nanotechnology 12/2009; 9(12):7090-3. · 1.56 Impact Factor
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ABSTRACT: Multi-walled carbon nanotubes (MWCNTs) were functionalized by radiation-induced graft polymerization of acrylic acid onto the surface of MWCNTs in order to improve their dispersibility in water. 1H NMR, Raman spectroscopy, TEM, and TGA techniques were used to characterize the resulting functionalized MWCNTs. The grafting degree was dependent on the grafting conditions such as the absorbed dose and the monomer concentration. The experimental results confirmed that poly(acrylic acid) chains were successfully grafted onto the surface of the MWCNTs. The poly(acrylic acid)-grafted MWCNTs showed a much better water dispersibility than the pristine MWCNTs.
Journal of Nanoscience and Nanotechnology 12/2009; 9(12):7126-9. · 1.56 Impact Factor
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The American Chemical Society; 01/2009
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ABSTRACT: This study examined the effects of the sodium salts of aliphatic dicarboxylic acids (DCAs) on the dynamic mechanical properties and morphology of two sets of poly(styrene-co-sodium methacrylate) (MNa) and poly(styrene-co-sodium styrenesulfonate) (SNa) ionomers. When the DCA content was relatively low, the ionic moduli of the MNa and SNa ionomers increased but the matrix and cluster glass transition temperature (T g ) did not change significantly. The increasing ionic modulus was almost independent of the type of the ionic groups of the ionomer, and the chain length of DCAs. When a large amount of the sodium succinate (DCA4) was added to the MNa and SNa ionomers, the ionic moduli of the two ionomers increased strongly but the matrix and cluster T g ’s increased slightly and significantly, respectively. In the case of sodium hexadecanedioate (DCA16), DCA16 increased the ionic moduli of the two ionomers. The addition of DCA16 changed the matrix and cluster T g ’s of the MNa ionomer slightly, but decreased the cluster T g of the SNa ionomer significantly with no change in the matrix T g . In addition, the DCA-containing ionomers showed an X-ray diffraction peak indicating the presence of ordered domains of DCAs in the ionomers. Hence, DCA4 acts mainly as a reinforcing filler in MNa and SNa systems. In the case of DCA16, it initially behaved like a filler but also functioned as a preferential plasticizer for the clusters at high content.
Macromolecular Research 01/2009; 17(9):658. · 1.15 Impact Factor
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ABSTRACT: The assembly of nanoparticles in topologically predefined superstructures is an important area in nanoscale architecture. In this paper, we report an unusual aggregation phenomenon involving L-lysine capped gold nanoparticles and human serum albumin into hollow nanospheres. The electrostatic interaction between positively charged L-lysine capped gold nanoparticles and negatively charged human serum albumin at physiological pH led to the assembly of the gold nanoparticles into hollow spheres. The phenomenon can be explained by the dry hole opening mechanism.
Nanotechnology 07/2008; 19(26):265603. · 3.98 Impact Factor
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ABSTRACT: Phase-separation behavior of polystyrene (PS) and poly(methyl methacrylate) (PMMA) 1:1 blend film has been studied as a function of film thickness and component by adding PS-b-PMMA diblock copolymer. After annealing, PS is phase-separated into circular-shaped bumps on a PMMA layer. The bump number is inversely proportional to the film thickness in log-log plot while the slope is invariable for the blends with and without 5% PS-b-PMMA diblock copolymer. The bump size and inter-bump spacing are also affected by both the film thickness and addition of the block copolymer.
Ultramicroscopy 06/2008; 108(10):1186-90. · 2.47 Impact Factor
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ABSTRACT: We have demonstrated that monolayer films of randomly charged polystyrene sulfonated acid (PSSA) can be produced by the Langmuir technique, and observed the micro-domain structures, produced by the phase separation of electrostatically charged moieties and the hydrophobic moieties. Using atomic force microscopy and Langmuir isotherm, we found three specific regimes for the polyelectrolytes with various degrees of sulfonation (4-35%); very low charged PSSA (4-5%) in the hydrophobic regime, moderately charged PSSA (6-16%) which possessed a well-balanced nature between electrostatic and the hydrophobic interactions, and strongly amphiphilic nature of PSSA (6-16%) in the ionomer regime. Finally, we could categorize PSSA 35% in the polyelectrolyte regime, due to the dominance of the electrostatic interactions over the hydrophobic interactions.
Ultramicroscopy 06/2008; 108(10):1191-5. · 2.47 Impact Factor
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ABSTRACT: The penetration of a transcription-activating factor (TAT)-derived, cell-penetration peptide onto 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dipalmitoyl-sn-glycero-3-[phospho-L-serine] (DPPS) monolayer on phosphate-buffered saline subphase was characterized. The surface area at the target pressure increased noticeably by the peptide penetration from the subphase to the phospholipid monolayer, which might suggest a direct penetration of the peptide across the pure phospholipid bilayer membrane. Interestingly, the more significant area increase at 35 mN/m was monitored from DPPC monolayer, contrary to the simple charge interaction: the net neutral DPPC, the net-negative DPPS, and the positive TAT-derived peptides (TDP). X-ray reflectivity measurements as well as the molecular area from pi (surface pressure)-A (area) isotherms suggest that the packing density of DPPS at the target pressure is too high to allow the effective penetration of the peptide into the monolayer and the positively charged peptides can be entrapped at the negative electrostatic well of DPPS headgroup layer, leading to the simple adsorption on the DPPS monolayer instead of penetration into it. Thus, more penetration with less adsorption of the peptide is induced by DPPC monolayer than DPPS monolayer.
Journal of Peptide Science 05/2008; 14(4):461-8. · 1.80 Impact Factor
