Biomedical subjects

Woo-Sik Kim

Publications and source records attributed to Woo-Sik Kim.

8 recordsLinked to original sources

PubMed2006

Long polymeric tips of atomic force microscopy for large biological samples.

We show a new atomic force microscopy technique for obtaining high-resolution topographic images of large bio-samples. To obtain high-resolution topographic images for the samples, we fabricated a long polymeric tip with a small protrusion using two-photon adsorbed photo-polymerization techniques. The obtained tip length was over 50 microm, and the tip was used directly to visualize COS-1 and 293 cells. Compared with commercial tips, the long tip made it easier to obtain topographic images of the large cells. In the magnified topographic images, the sub-100-nm resolution was confirmed with the long tips. This long probe tip is expected to broaden large sample-related studies and applications in the future.

Animals↗

PubMed2005

Morphological control of calcium carbonate crystallized in reverse micelle system with anionic surfactants SDS and AOT.

The influence of a surfactant over water on the polymorphism and crystal size of calcium carbonate produced by reaction crystallization in microemulsion systems was investigated in a mixing tank reactor. The crystallization was induced by the reaction between two aqueous micelle solutions (Na2CO3-CaCl2) stabilized by anionic surfactants, SDS (sodium dodecyl sulfate) or AOT (sodium bis(2-ethylhexyl) sulfosuccinate). With increasing surfactant ratio to water, the water-in-oil microemulsion was stably developed and the morphology of the calcium carbonate crystallized in the micelles sharply transformed from calcite to vaterite. The influence of SDS on the polymorphism and crystal size of calcium carbonate was much clearer than that of AOT. In addition, with AOT, certain step changes in the morphology and crystal size occurred around a surfactant ratio to water (R=[H2O]/[surfactant]) of 15 due to a two-phase separation of the microemulsion.

Journal Article↗

PubMed2005

Preparation of large monodispersed spherical silica particles using seed particle growth.

To obtain large-sized, monodispersed spherical particles of silica by sol precipitation, a seed particle growth method was attempted. The formation of secondary particles during seed particle growth causing a multimodal distribution of particle size was suppressed via fine adjustment of the reaction conditions, such as TEOS, ammonia, and water concentrations, as well as operational conditions such as feeding time and agitation speed. Among the reaction conditions, an increase of TEOS concentration promoted secondary particle formation, resulting in bimodal particle distribution. However, secondary particle formation was depressed with increasing ammonia and water concentrations. In addition, long feeding time (low feed flow rate) and rigorous agitation significantly reduced secondary particle formation because they contributed to the slow generation of supersaturation and rapid seed particle growth, respectively.

Journal Article↗

PubMed2005

Surface-functionalized nanoparticles for controlled drug delivery.

Nanoparticles have been extensively investigated in drug-delivery systems. Especially, the effectiveness of the surface-functionalized nanoparticles, which consist of copolymers with functional molecules, is well demonstrated. This chapter describes the complete technique for the preparation of surface-functionalized nanoparticles. Tetracycline with an affinity to bone was chosen as a model material for surface functionalization. There are two steps for the preparation of tetracycline-modified nanoparticles. The first step is the conjugation of poly(D,L-lactide-co- glycolic acid) with tetracycline via carbodiimide chemistry and is the most often employed. Three kinds of techniques--the emulsification-diffusion method, nanoprecipitation, and the dialysis method are used for nanoparticle formation of the resulting copolymer. Prepared nanoparticles having a size <200 nm and a hydrophilic surface layer can be applied for bone-specific drug delivery.

Animals↗

PubMed2004

Chemoenzymatic synthesis of sugar-containing biocompatible hydrogels: crosslinked poly(beta-methylglucoside acrylate) and poly(beta-methylglucoside methacrylate).

Sugar-containing biocompatible hydrogels were synthesized chemoenzymatically by the following two steps: 1. lipase-catalyzed esterification of beta-methylglucoside with acrylic acid/methacrylic acid/vinyl acrylate/vinyl methacrylate in solvent as well as solvent-free process for the formation of sugar-containing monomers; and 2. polymerization process by free-radical polymerization with and without a crosslinker, ethylene glycol dimethacrylate (EGDMA). The solvent-free process resulted in an initial reaction rate approximately 1.5-2 times faster than that of the solvent process along with a complete consumption of beta-methylglucoside during the alcoholysis. The presence of pendant vinyl groups in beta-methylglucoside acrylate (MGAA) and beta-methylglucoside methacrylate (MGMAA) was confirmed by (1)H/(13)C NMR analysis, whereas the successful polymerization with the consumption of the vinyl groups was confirmed by Fourier transform infrared spectroscopy and (13)C NMR spectra. The surfaces of both poly(MGAA) and poly(MGMAA) were analyzed using scanning electron microscopy. The increased contents of EGDMA resulted in a higher tensile strength as well as a reduced swelling ratio of poly(MGAA) and poly(MGMAA). The swelling exponents were within the range of 0.53 and 0.98. In vitro cytotoxicity tests by MTT assay exhibited >90% cell viability in the poly(MGAA) and poly(MGMAA) without EGDMA, whereas a significantly decreased cell viability was observed for those with EGDMA.

Acrylates↗

PubMed2004

Probing crystallization of calcium oxalate monohydrate and the role of macromolecule additives with in situ atomic force microscopy.

Kidney stones are crystal aggregates, most commonly containing calcium oxalate monohydrate (COM) microcrystals as the primary constituent. Macromolecules, specifically proteins rich with anionic side chains, are thought to play an important role in the regulation of COM growth, aggregation, and attachment to cells, all key processes in kidney stone formation. The microscopic events associated with crystal growth on the [010], [121], and [100] faces have been examined with in situ atomic force microscopy (AFM). Lattice images of each face reveal two-dimensional unit cells consistent with the COM crystal structure. Each face exhibits hillocks with step sites that can be assigned to specific crystal planes, enabling direct determination of growth rates along specific crystallographic directions. The rates of growth are found to depend on the degree of supersaturation of calcium oxalate in the growth medium, and the growth rates are very sensitive to the manner in which the growth solutions are prepared and introduced to the AFM cell. The addition of macromolecules with anionic side chains, specifically poly(acrylic acid), poly(aspartic acid), and poly(glutamic acid), results in inhibition of growth on the hillock step planes. The magnitude of this effect depends on the macromolecule structure, macromolecule concentration, and the identity of the step site. Poly(acrylic acid) was the most effective inhibitor of growth. Whereas poly(aspartic acid) inhibited growth on the (021) step planes of the (100) hillocks more than poly(glutamic acid), the opposite was found for the same step planes on the (010) hillocks. This suggests that growth inhibition is due to macromolecule binding to both planes of the step site or pinning of the steps due to binding to the (100) and (010) faces alone. The different profiles observed for these three macromolecules argue that local binding of anionic side chains to crystal surface sites governs growth inhibition rather than any secondary polymer structure. Growth inhibition by cationic macromolecules is negligible, further supporting an important role for proteins rich in anionic side chains in the regulation of kidney stone formation.

Journal Article↗

PubMed2004

Modification of surface crystal formation on mother crystal by additive molecules.

Additive molecules and excess reactant species (NaOH and NH4F) in NaF crystallization were used to control surface crystal formation on a mother crystal. When the surface integration was inhibited or bulk diffusion facilitated, more surface crystals were found on the mother crystal due to an increase in the interfacial supersaturation on the crystal. The inclusion of KCl as an additive and increases in the reactant concentration and agitation speed resulted in a higher population of surface crystals on the mother crystal, because surface integration was inhibited. However, surface crystal formation was suppressed by the polymer gelatin due to retardation of the bulk diffusion by the gelatin layer formed around the crystal. In addition, surface crystal formation significantly changed according to the feeding mode, and the excess species of NaOH originating from the NH4F feeding mode were more effective in facilitating surface crystal formation than the excess species of NH4F coming from the NaOH feeding mode due to the smaller ionic radii of NaOH than of NH4F.

Journal Article↗

PubMed2004

Enzymatic esterification of beta-methylglucoside with acrylic/methacrylic acid in organic solvents.

The enzymatic esterifications of beta-methylglucoside with acrylic acid/methacrylic acid were carried out using Novozym 435. t-Butanol indicating the highest conversion value was determined as an optimal solvent. The molar ratio (beta-methylglucoside:acids) of 1:15 was most favorable to the esterification. The enzyme concentration of 5% (w/v), and the temperature (50 degrees C for beta-methylglucoside:acrylic acid, 45 degrees C for beta-methylglucoside:methacrylic acid) resulted in the highest final conversion. Beta-methylglucoside of 60gl(-1) was found to be most effective in terms of short reaction time as well as product concentrations. Under these conditions, the maximum conversions for the esterification of beta-methylglucoside with acrylic acid and beta-methylglucoside with methacrylic acid were 59.3% after 12h and 71.3% after 72h, respectively. The structural analysis of the products was performed by FT-IR spectroscopy and (1)H NMR.

Acrylates↗