Gahee Kim

The biocompatability of mesoporous inorganic-organic hybrid resin films with ionic and hydrophilic characteristics.

New mesoporous silicate-titania resin systems hybridized with 4,5-dihydroxy-m-benzenedisulfonic acid and poly(ethylene glycol)-dimethacrylate component were developed. These inorganic-organic hybrid resins were found to reveal highly controlled ionic and hydrophilic surface with excellent durability and adhesion onto various substrates. The resin films revealed high resistance to nonspecific adsorption of fibrinogen and to adherence by several bacterial pathogens such as Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. Furthermore, excellent biocompatibility of the developed resins was proved by both HEp-2 cell adhesion in vitro and subcutaneous implantation in mice. The inorganic-organic hybrid resins are strongly promising for biomedical applications including biomedical devices and biosensors.

Two-Dimensionally Well-Ordered Multilayer Structures in Thin Films of a Brush Polypeptide

In this study, we report the first production of two-dimensionally well-ordered molecular multilayers (i.e., with a well-defined molecular lamellar structure) based on the antiparallel beta-sheet chain conformation in thin films of a brush polypeptide, poly(S-n-hexadecyl-dl-homocysteine) (PHHC), through the use of a simple spin-coating process and the quantitative structural and property analysis of the thin films using a grazing incidence X-ray scattering technique combined with Fourier transform infrared spectroscopy and differential scanning calorimetry. These analyses provide detailed information about the structure and molecular conformation of the self-assembled lamellae in the PHHC thin film, which is not easily obtained using conventional techniques. Moreover, we used the in situ measurements carried out at various temperatures and the data analyses to establish mechanisms for the evolution of the self-assembled lamellar structures in the film and for their melting. In addition, we propose molecular structure models of the PHHC polymer molecules in the thin film at various temperatures.

The biocompatibility of self-assembled brush polymers bearing glycine derivatives

We have synthesized brush polymers with various glycine derivatives as the end groups of their long alkyl bristles. The polymers are thermally stable up to 170-210 degrees C and form good quality films through conventional spin- or dip-coating and subsequent drying. Interestingly, the thin films of these brush polymers exhibit different molecular multi-layer structures that arise through the efficient self-assembly of the bristles with glycine derivative end groups. These brush polymer films have hydrophilic surfaces and exhibit some water sorption. The extent of the water sorption by these films depends upon the nature of the glycine derivatives in the bristle end. These films not only repel fibrinogen molecules and platelets from their surfaces, but also have high resistance to bacterial adherence. Moreover, the films were found to provide conducive surface environments for the successful anchoring and growth of HEp-2 cells, and to exhibit excellent biocompatibility in mice. These brush polymers have potential uses in biomedical applications including medical devices, especially blood contacting devices such as catheters, stents, blood vessels, and biosensors, due to their enhanced biocompatibility and the reduced possibility of post-operative infection.

Molecular Fibers Based on the Honeycomb-Like Self-Assembly of an α-Helical Polypeptide

We have succeeded in fabricating well-grown molecular fibers of a polypeptide on substrates by using a conventional solution spin-coating and drying process. These molecular fibers were found to consist of a honeycomb-like molecular assembly formed via the hexagonal close packing of the polypeptide chains in the alpha-helix conformation.

New self-assembled brush glycopolymers: Synthesis, structure and properties

A new series of chemically well-defined brush glycopolymers consisting of a polyoxyethylene backbone and bristles bearing glycosyl and methyl end groups was synthesized with various compositions. The glycopolymers were thermally stable up 200 °C and were soluble in a variety of common solvents. The brush polymer films formed multibilayer structures, the layers of which were stacked along the direction normal to the film plane so as to display a glycosyl group-rich surface or a methyl group-rich surface or their mixture, depending on the bristle end group composition. The multibilayer structures were stabilized by the self-assembly of the bristles via lateral packing. The glycosyl-rich surface played a critical role in enhancing the surface hydrophilicity and water sorption to a certain level; thus, the glycopolymer films easily formed a hydration layer to a certain depth on the film surface. The hydrophilic surfaces and hydration layer efficiently prevented protein adsorption onto the brush glycopolymers and suppressed bacterial adherence while promoting mammalian cell adhesion and displaying excellent biocompatibility in an in vivo mouse study.

Synchrotron X-ray scattering studies on the structural evolution of microbial poly(3-hydroxybutyrate)

The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) was studied in detail using time-resolved small-angle X-ray scattering. This polyester was found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the polyester was always larger than that of the amorphous layers. Secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.

Structural analysis of thin films of novel polynorbornene derivatives by grazing incidence X-ray scattering and specular X-ray reflectivity along with ellipsometry

In the present study, structural analyses using synchrotron grazing incidence X-ray scattering, specular reflectivity and ellipsometry were performed on thin films of two novel polynorbornene derivatives, chiral poly(norbornene acid methyl ester) and racemic poly(norbornene acid n-butyl ester), which are potential low dielectric constant materials for advanced microelectronic and display applications. These analyses provided important information on the structure, electron density gradient across the film thickness, chain orientation, refractive index and thermal expansion characteristics of the polymers in substrate-supported thin films. The structural characteristics and properties of the thin films depended on the tacticity of the polymer chain and were further influenced by the film thickness and thermal annealing history.