Plasma-on-chip device for stable irradiation of cells cultured in media with a low-temperature atmospheric pressure plasma.

We have developed a micro electromechanical systems (MEMS) device which enables plasma treatment for cells cultured in media. The device, referred to as the plasma-on-chip, comprises microwells and microplasma sources fabricated together in a single chip. The microwells have through-holes between the microwells and microplasma sources. Each microplasma source is located on the backside of each microwells. The reactive components generated by the microplasma sources pass through the through-holes and reach cells cultured in the microwells. In this study, a plasma-on-chip device was modified for a stable plasma treatment. The use of a dielectric barrier discharge (DBD) technique allowed a stable plasma treatment up to 3 min. The plasma-on-chip with the original electrode configuration typically had the maximum stable operation time of around 1 min. Spectral analysis of the plasma identified reactive species such as O and OH radicals that can affect the activity of cells. Plasma treatment was successfully performed on yeast (Saccharomyces cerevisiae) and green algae (Chlorella) cells. While no apparent change was observed with yeast, the treatment degraded the activity of the Chlorella cells and decreased their fluorescence. The device has the potential to help understand interactions between plasma and cells.

Effective Reduction of Volumetric Thermal Expansion of Aromatic Polyimide Films by Incorporating Interchain Crosslinking.

To develop a facile method for reducing the coefficient of volumetric thermal expansion (CVE) of polymer films, the thermal expansion behaviors of thermally cross-linkable polyimide (PI) films with isomeric diamine structures were investigated via thermal mechanical analyses and optical interferometry measurements. The degree of crosslinking of the PI films containing the diphenylethynylene (Ph⁻C≡C⁻Ph) structure in the main chain was characterized by far-infrared (far-IR) spectra and density functional theory (DFT) calculations, and variations in the CVE induced by thermal crosslinking were quantitatively estimated. The crosslinking reactions effectively reduced the CVEs of the PI films by suppressing intermolecular free volume expansion and local molecular motions promoted at elevated temperatures. The lowest CVE value observed for a crosslinked PI cured at 400 °C (+98 ppm/K at 80⁻280 °C) was one of the smallest values reported to date in polymers. Incorporating interchain crosslinking into the main chain is an effective method for reducing the CVE of aromatic polymers.