Asko Sneck

Genotoxic and inflammatory effects of nanofibrillated cellulose in murine lungs.

Nanofibrillated cellulose (NFC) is a sustainable and renewable nanomaterial, with diverse potential applications in the paper and medical industries. As NFC consists of long fibres of high aspect ratio, we examined here whether TEMPO-(2,2,6,6-tetramethyl-piperidin-1-oxyl) oxidised NFC (length 300–1000nm, thickness 10–25nm), administrated by a single pharyngeal aspiration, could be genotoxic to mice, locally in the lungs or systemically in the bone marrow. Female C57Bl/6 mice were treated with four different doses of NFC (10, 40, 80 and 200 µg/mouse), and samples were collected 24h later. DNA damage was assessed by the comet assay in bronchoalveolar lavage (BAL) and lung cells, and chromosome damage by the bone marrow erythrocyte micronucleus assay. Inflammation was evaluated by BAL cell counts and analysis of cytokines and histopathological alterations in the lungs. A significant induction of DNA damage was observed at the two lower doses of NFC in lung cells, whereas no increase was seen in BAL cells. No effect was detected in the bone marrow micronucleus assay, either. NFC increased the recruitment of inflammatory cells to the lungs, together with a dose-dependent increase in mRNA expression of tumour necrosis factor &agr;, interleukins 1&bgr; and 6, and chemokine (C-X-C motif) ligand 5, although there was no effect on the levels of the respective proteins. The histological analysis showed a dose-related accumulation of NFC in the bronchi, the alveoli and some in the cytoplasm of macrophages. In addition, neutrophilic accumulation in the alveolar lung space was observed with increasing dose. Our findings showed that NFC administered by pharyngeal aspiration caused an acute inflammatory response and DNA damage in the lungs, but no systemic genotoxic effect in the bone marrow. The present experimental design did not, however, allow us to determine whether the responses were transient or could persist for a longer time.

Suitability of roll-to-roll reverse offset printing for mass production of millimeter-wave antennas: Progress report

In this work, we investigate different printing technologies suitable for mass production of millimeter-wave antennas and other devices, e.g., holograms and frequency selective absorbers, on flexible substrates. We concentrate especially on roll-to-roll reverse offset printing. The driving factors are low cost, high accuracy, high efficiency, and reliable performance. Therefore, we need to find and characterize suitable flexible substrates (permittivity and loss tangent at mm-wavelengths), conducting inks (viscosity, surface resistance of the resulting conducting layer), adhesion of the ink to the substrate, and feature size capable for printing mm-wave antennas and other passive devices in high volumes.

Fractionation of Nanocellulose by Foam Filter

The foam fractionation method was applied for nanocellulose. Experiments were carried out with enzymatically pretreated nano-fibrillated cellulose (NFC) from softwood, as well as commercial products. Narrow channels (plateaus) between bubbles prevent the flow of coarse particles along the water, so that foam acts like a filter. The advantage of the method is no risk of clogging, which could be a big problem for conventional filters or screens. Mean particle size (effective size by means of dynamic light scattering measurement) was reduced by foam fractionation, and the reduction range depended on the cellulose grade and the type of surfactant. The yield turned out to be low, probably because of particle aggregation due to the interaction with surfactant.

Towards printed millimeter-wave components: Material characterization

This paper presents the results from evaluation of suitable materials and ink properties for printing millimeter wave components. Dielectric parameters (relative permittivity and loss tangent) of various potential substrate materials are extracted from S-parameter measurements and simulations. Test samples have been printed over Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN) substrates and the measurement of the ink properties have been carried out.

Systematic Design of Printable Metasurfaces: Validation Through Reverse-Offset Printed Millimeter-Wave Absorbers

In this paper, we present a systematic methodology for realizing desired sheet impedances of printable metasurfaces. This methodology allows independent control of the sheet reactance (capacitance and series inductance) and its resistance, even if the conductor properties as well as the dielectric substrate thickness and permittivity are fixed due to manufacturing process restrictions. The derived analytical formulas allow us to easily find the physical dimensions of conductive patterns, which implement the required surface impedance. Numerical verification of the method shows excellent agreement with the analytical predictions, allowing the design of an arbitrary impedance without any optimization process. The method can be applied for designing lossy and low-loss metasurfaces, which can be used for absorption and wavefront manipulation of electromagnetic waves. As a representative example, the design of thin perfect absorbers has been approached using the developed method. The results demonstrate that the methodology adapts various material sheet resistivity, opening new possibilities for the design of printable metasurfaces, where the sheet resistivity of conductor strongly depends on the specific printing method. Finally, an experimental validation of absorbers designed for millimeter waves and printed using reverse-offset techniques is presented. To the best of our knowledge, this is the first time when reverse-offset printing has been used to provide well-working devices for short millimeter waves.

Reverse Offset Printing of Semidried Metal Acetylacetonate Layers and Its Application to a Solution-Processed IGZO TFT Fabrication

The submicrometer resolution printing of various metal acetylacetonate complex inks including Fe, V, Mn, Co, Ni, Zn, Zr, Mo, and In was enabled by a robust ink formulation scheme which adopted a ternary solvent system where solubility, surface wettability, and drying as well as absorption behavior on a polydimethylsiloxane sheet were optimized. Hydrogen plasma in heated conditions resulted in bombarded, resistive, or conductive state depending on the temperature and the metal species. With a conductivity-bestowed layer of MoO x and a plasma-protecting layer of ZrO x situated on the top of an IGZO layer, a solution-processed TFT exhibiting an average mobility of 0.17 cm2/(V s) is demonstrated.

Studies on applicability of reverse offset in printing millimeter-wave antennas on flexible substrates

We investigate the applicability of roll-to-roll reverse offset printing for fabrication of millimeter-wave antennas on flexible substrates. The aim is to find a fabrication method for mass production of such antennas; therefore, attention should be paid on such factors as cost, efficiency, and reliable performance of the printed antennas.