Sang-Hee Lee

Melanin-like nanoparticles were synthesized with size control through neutralization of dopamine hydrochloride with NaOH, followed by spontaneous air oxidation of dopamine. Although the particle characteristic of natural melanins was understood to be significantly affected by the biological and structural environment, melanin-lke nanoparticles can be realized through the chemical reactions only. Melanin-like nanoparticles that are <100 nm showed excellent dispersion stability in water as well as biological media and good biocompatibility to HeLa cells after the appropriate surface modification with thiol-terminated methoxy-poly(ethylene glycol) (mPEG-SH). Furthermore, the demonstrated ability of melanin-like nanoparticles to reduce 2,2-diphenyl-1-picrylhydrazyl (DPPH) suggests free radical scavenging activity of the material.

We fabricated magnetorheological elastomer (MRE) films consisting of polydimethylsiloxane and various concentrations of fluorinated carbonyl iron particles. The application of a magnetic field to the MRE film induced changes in the surface morphology due to the alignment of the iron particles along the magnetic field lines. At low concentrations of iron particles and low magnetic field intensities, needle-like microstructures predominated. These structures formed more mountain-like microstructures as the concentration of iron particles or the magnetic field intensity increased. The surface roughness increased the water contact angle from 100° to 160° and decreased the sliding angle from 180° to 10°. The wettability and adhesion properties changed substantially within a few seconds simply upon application of a magnetic field. Cyclical measurements revealed that the transition was completely reversible.

A CO2 laser was employed to create a rectangle (4 × 2 mm2) of a conductive graphitic carbon layer (GCL) directly on a cellulose substrate. By tilting the substrate while keeping the laser power constant, the laser power density was gradually changed while scanning in the direction of the long side of the rectangle, due to deviation of the laser focus. As the laser beam defocus distance increased, the laser intensity at the substrate decreased, and the oxygen-to-carbon ratio (O/C) of the GCL increased. Upon exposing the GCL substrate to water vapor, the hydrogen-containing groups (carboxyl and hydroxyl groups) in the GCL were hydrolyzed, and a density gradient of hydrogen ions was induced due to the preformed O/C gradient. The resulting voltage and current outputs reached 0.23 V and 0.4 μA/cm2, respectively, at 70% relative humidity. Additionally, it was demonstrated that the electricity obtained during breathing could turn on a green light-emitting diode operating at an onset potential of 2 V when an array of the GCLs was attached to a filter mask.