Kosuke Kuwabara

Cell Culture on Nanopillar Sheet: Study of HeLa Cells on Nanopillar Sheet

This is the first report of the successful culturing of HeLa cells on nanopillar sheets–a new type of cell culture dish–in a different way from that on flat petri dishes. Nanopillar sheets were fabricated with a high-aspect ratio structure with a diameter of 80–1000 nm and a height of 1–3 µm using nanoprint technology. Nanopillar structure with 500 nm diameter and 1 µm height enabled easy subculture of the cells from the sheets without the conventional trypsinization method. Moreover, the HeLa cells divided and proliferated on the sheets in the same way as on the flat surfaces with different manner of adhesion.

Nanopillar sheets as a new type of cell culture dish: detailed study of HeLa cells cultured on nanopillar sheets.

Nanopillar sheets were fabricated with high-aspect ratio structures with a diameter of 160–1000 nm and a height of 1 μm by nanoimprinting. The suitability of nanopillar sheets as a new type of cell culture dish was examined by studying the behavior of HeLa cells cultured on the sheets using light microscopy, scanning electron microscopy, and fluorescence microscopy observing actin and vinculin molecules. The nanopillar structure enabled easy subculture of the cells from the sheets without conventional trypsinization. Moreover, the HeLa cells divided and proliferated on the sheets in a different way to that found on petri dish because of the manner in which the cells adhered to the materials.

Enhancement of fluorescence intensity from an immunoassay chip using high-aspect-ratio nanopillars fabricated by nanoimprinting

High-aspect-ratio structures (nanopillars) were used to enhance the fluorescence intensity of immunoassay chips. Nanoimprinting with elongation phenomenon was applied to fabricate polystyrene nanopillars. Human alpha fetoprotein was detected by a fluorescence immunoassay protocol. Fluorescence intensities were evaluated for areas with nanopillars of different surface areas. The area with nanopillars of 95nm diameter and 4.1μm height showed fluorescence intensity 34 times higher than that of flat areas.

High-aspect-ratio nanopillar structures fabricated by nanoimprinting with elongation phenomenon

The authors found that fine pillar structures (nanopillars) with a high aspect ratio were formed by nanoimprinting with elongation phenomenon. Polymer nanopillars with higher aspect ratios than that of corresponding holes on the mold were obtained without any etching processes after nanoimprinting. The finest nanopillars were 95 nm in diameter and 4.1 μm high made of polystyrene. Elongated nanopillars of poly(methylmethacrylate) and polystyrene were confirmed. Elongation of nanopillars depended on process conditions such as the diameter of holes on the mold, the unmolding temperature, and the molecular weight of the polymer resin.

Developments of nanoimprint technologies and applications

The nanoimprint technology is attractive for the fabrication of nano-scale structures in view of cost and mass production. There are several points for the industrial applications such as pattern formation area, resolution, residual layer thickness, precise control of pattern transfer, lifetime of mold, alignment and so on. A thermal nanoimprint system, which can imprint fine dots on a 300 mm diameter wafer in a single step, is developed. The narrow pith patterns for future storage and IT devices are formed on a polymer layer. A high-aspect nanoprint (Hi-NP) technology forms polymer nanopillars with high aspect ratio. The nanopillars are applied to a bio-chip for the fluorescence immunoassay. The chip is effective in the enhancement of the fluorescence intensities, since the nanopillars enlarge the surface area.

Fluorescence measurement of nanopillars fabricated by high aspect nanoprint technology

In this paper, our aim is to form high aspect structures (nanopillars) by high aspect nanoprint (Hi-NP) technology.

In Situ Stress Measurements during Welding Process

Welding technologies are indispensable for fabricating various industrial structures and must be highly reliable. Since tensile residual stresses at surface after welding cause crack progress, it is important to understand how stresses built up during the welding process in order to optimize final residual stresses as reduced tensile or introduced compressive stresses. Therefore, we conducted in-situ measurements of phase transformations, stresses and temperatures during tungsten inert gas (TIG) welding to understand how stresses built up. X-ray diffraction rings were detected per 0.1 sec during TIG welding by using a large-area two-dimensional detector and the accuracy of the stress analysis was estimated to be 8 MPa using the sin2ψ technique. In this paper, we described the phase transformations of ferrite low-carbon rolled steel and the changes in stresses during TIG welding.

Degradation behavior of release layers for nanoimprint lithography formed on atomically flat Si(111) terraces

A release layer for nanoimprint lithography was formed on atomically flat Si(111) terraces to investigate its surface morphology and degradation behavior due to imprinting. The adhesive nature between the layers and a polystyrene colloid probe was also evaluated. Three types of release layers (silicone, fluoro-oligomer, and perfluoropolyether) were formed on mildly oxidized Si(111) substrates that retained a flat terrace structure. All the layers were sufficiently thin and uniform to show the flat terrace structure of the Si(111) substrates. These release layers showed different degradation behaviors toward thermal nanoimprint lithography and UV-photocure nanoimprint lithography cycles as elucidated by x-ray photoelectron spectroscopy, atomic force microscopy, and adhesion force measurements. The perfluoropolyether exhibited better durability against nanoimprint cycles due to the presence of free molecules not bound to the surface. This study includes a detailed discussion of the degradation mechanisms of...

Resin Elongation Phenomenon of Polystyrene Nanopillars in Nanoimprint Lithography

We investigated the elongation of polystyrene nanopillars formed by thermal nanoimprint lithography. Silicone and perfluoropolyether were used as mold release agents to obtain molds with different adhesion forces against polystyrene to be imprinted. The adhesion force between the resin and release layers was evaluated as a force curve by atomic force microscope with a polystyrene colloid probe. Elongation depended on the aspect ratio of the corresponding microholes on the mold and the adhesion force against the release layer. The conditions under which the elongation occurred exhibited a clear threshold on the stress loaded on the foot area of the nanopillars.