Helium Cold Atmospheric Plasma Causes Morphological and Biochemical Alterations in Candida albicans Cells.

(1) Background: Previous studies reported the promising inhibitory effect of cold atmospheric plasma (CAP) on Candida albicans. However, the exact mechanisms of CAP's action on the fungal cell are still poorly understood. This study aims to elucidate the CAP effect on C. albicans cell wall, by evaluating the alterations on its structure and biochemical composition; (2) Methods: C. albicans cells treated with Helium-CAP were analyzed by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) in order to detect morphological, topographic and biochemical changes in the fungal cell wall. Cells treated with caspofungin were also analyzed for comparative purposes; (3) Results: Expressive morphological and topographic changes, such as increased roughness and shape modification, were observed in the cells after CAP exposure. The alterations detected were similar to those observed after the treatment with caspofungin. The main biochemical changes occurred in polysaccharides content, and an overall decrease in glucans and an increase in chitin synthesis were detected; (4) Conclusions: Helium-CAP caused morphological and topographic alterations in C. albicans cells and affected the cell wall polysaccharide content.

Study of a Conical Plasma Jet with a Cloth-Covered Nozzle for Polymer Treatment.

Although atmospheric pressure plasma jets (APPJs) have been widely employed for materials modification, they have some drawbacks, such as the small treatment area (couple of cm2). To overcome this limitation, a funnel-like APPJ with a wide exit has been proposed. In this work, a gas-permeable cotton cloth covered the nozzle of the device to improve the gas flow dynamics and increase its range of operation. The funnel jet was flushed with Ar, and the plasma was ignited in a wide range of gas flow rates and the gap distances between the exit nozzle and the sample holder. The device characterization included electric measurements and optical emission spectroscopy (OES). To evaluate the size of the treatment and the degree of surface modification, large samples of high-density polyethylene (PE) were exposed to plasma for 5 min. Afterward, the samples were analyzed via water contact angle WCA measurements, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It was found that surface modification occurs simultaneously on the top and bottom faces of the samples. However, the treatment incorporated different functional groups on each side.

Simultaneous Treatment of Both Sides of the Polymer with a Conical-Shaped Atmospheric Pressure Plasma Jet.

A conical-shaped atmospheric pressure plasma jet (CS-APPJ) was developed to overcome a standard limitation of APPJs, which is their small treatment area. The CS-APPJs increase the treatment area but use the same gas flow. In the present work, polypropylene samples were treated by CS-APPJ and characterized by scanning electron microscope (SEM), the contact angle, Fourier-transformed infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). It was observed that the treatment co-occurs on the face directly in contact with the plasma and on the opposite face (OF) of the samples, i.e., no contact. However, the treatment changed the chemical composition on each side; the OF is rougher than the direct contact face (DCF), probably due to the oxygen groups in excess at the DCF and nitrogen in quantity at the OF. Although simultaneous treatment of both sides of the sample occurs for most atmospheric plasma treatments, this phenomenon is not explored in the literature.

Correlative light-electron fractography for fatigue striations characterization in metallic alloys.

The correlative light-electron fractography technique combines correlative microscopy concepts to the extended depth-from-focus reconstruction method, associating the reliable topographic information of 3-D maps from light microscopy ordered Z-stacks to the finest lateral resolution and large focus depth from scanning electron microscopy. Fatigue striations spacing analysis can be precisely measured, by correcting the mean surface tilting with the knowledge of local elevation data from elevation maps. This new technique aims to improve the accuracy of quantitative fractography in fatigue fracture investigations.

Correlative fractography: combining scanning electron microscopy and light microscopes for qualitative and quantitative analysis of fracture surfaces.

Correlative fractography is a new expression proposed here to describe a new method for the association between scanning electron microscopy (SEM) and light microscopy (LM) for the qualitative and quantitative analysis of fracture surfaces. This article presents a new method involving the fusion of one elevation map obtained by extended depth from focus reconstruction from LM with exactly the same area by SEM and associated techniques, as X-ray mapping. The true topographic information is perfectly associated to local fracture mechanisms with this new technique, presented here as an alternative to stereo-pair reconstruction for the investigation of fractured components. The great advantage of this technique resides in the possibility of combining any imaging methods associated with LM and SEM for the same observed field from fracture surface.

Extended depth from focus reconstruction using NIH ImageJ plugins: quality and resolution of elevation maps.

In this work, NIH ImageJ plugins for extended depth-from-focus reconstructions (EDFR) based on spatial domain operations were compared and tested for usage optimization. Also, some preprocessing solutions for light microscopy image stacks were evaluated, suggesting a general routine for the ImageJ user to get reliable elevation maps from grayscale image stacks. Two reflected light microscope image stacks were used to test the EDFR plugins: one bright-field image stack for the fracture of carbon-epoxy composite and its darkfield corresponding stack at same (x,y,z) spatial coordinates. Image quality analysis consisted of the comparison of signal-to-noise ratio and resolution parameters with the consistence of elevation maps, based on roughness and fractal measurements. Darkfield illumination contributed to enhance the homogeneity of images in stack and resulting height maps, reducing the influence of digital image processing choices on the dispersion of topographic measurements. The subtract background filter, as a preprocessing tool, contributed to produce sharper focused images. In general, the increasing of kernel size for EDFR spatial domain-based solutions will produce smooth height maps. Finally, this work has the main objective to establish suitable guidelines to generate elevation maps by light microscopy.

Low voltage and variable-pressure scanning electron microscopy of fractured composites.

Uncoated fracture surfaces of carbon-epoxy composites are investigated using a variable-pressure environmental scanning electron microscope (VP-ESEM), under optimized conditions for topographic description, image quality and sample preservation. Always using freeware or open source programs, parameters for low-voltage and low vacuum are stipulated with the support of Monte Carlo simulations combined to topographic measurements, tailoring the VP-ESEM setup for visualization of fine relief details. Based on topographic information from atomic force microscope (AFM) images, finest fracture steps were measured. These were the references to optimize and define boundaries for applied beam voltages and chamber pressures, restricted by the beam penetration depth and gas-electron interactions, guided by Monte Carlo simulations and signal-to-noise measurements. For VP mode, ideal chamber pressure was found around 30-40Pa at 3keV beam voltage and 6mm working distance. Lower pressures will cause noise due to electron charging and gas excess provokes resolution degradation and noise due to positive charging and electron beam scattering, raising the skirt radius. When a larger working distance is necessary, it can be compensated by adjusting the detector bias and the probe current, or even lowering chamber pressure, but the signal-to-noise ratio will certainly change. Monte Carlo simulations provided a good approach to optimize imaging conditions under low vacuum and low voltage for fractographic analysis of carbon-epoxy composites.

Eficiência de algumas barreiras cervicais utilizadas durante o clareamento interno / The eficiency of some cervical barriers into internal bleaching

Quarenta e dois caninos superiores receberam como barreira cervical: cimpat blanc, resina flow, cimento de fosfato de zinco e cimento de ionômero de vidro. Após quatro sessões de clareamento, foi injetado azul de metileno a 2% nas câmaras pulpares sob vácuo, permanecendo por 24 horas. Clivados, foram fotografados por uma câmera digital acoplada a uma lupa estereoscópica e atribuídos escores à infiltração do corante. Os resultados foram submetidos ao teste de Kruskal-Wallis, sendo significantes em nível de 5%. A menor infiltração foi alcançada pelo cimento de ionômero de vidro, entretanto nenhum material foi totalmente eficaz em impedir a infiltração do corante.