In vivo confirmation of hydration-induced changes in human-skin thickness, roughness and interaction with the environment

Skin properties, structure and performance can be influenced by many internal and external factors, such as age, gender, lifestyle, skin diseases and a hydration level that can vary in relation to the environment. The aim of this work was to demonstrate the multifaceted influence of water on human skin through a combination of in vivo confocal Raman spectroscopy and images of volar-forearm skin captured with laser scanning confocal microscopy. By means of this pilot study, we have both qualitatively and quantitatively studied the influence of changing the depth-dependent hydration level of the stratum corneum (SC) on the real contact area (RCA), surface roughness and the dimensions of the primary lines and presented a new method for characterising the contact area for different states of the skin. The hydration level of the skin and the thickness of the SC increased significantly due to uptake of moisture derived from liquid water or, to a much lesser extent, from humidity present in the environment. Hydrated skin was smoother and exhibited higher RCA values. The highest rates of water uptake were observed for the upper few μm of skin and for short exposure times

Steering surface topographies of electrospun fibers: understanding the mechanisms

A profound understanding of how to tailor surface topographies of electrospun fibers is of great importance for surface sensitive applications including optical sensing, catalysis, drug delivery and tissue engineering. Hereby, a novel approach to comprehend the driving forces for fiber surface topography formation is introduced through inclusion of the dynamic solvent-polymer interaction during fiber formation. Thus, the interplay between polymer solubility as well as computed fiber jet surface temperature changes in function of time during solvent evaporation and the resultant phase separation behavior are studied. The correlation of experimental and theoretical results shows that the temperature difference between the polymer solution jet surface temperature and the dew point of the controlled electrospinning environment are the main influencing factors with respect to water condensation and thus phase separation leading to the final fiber surface topography. As polymer matrices with enhanced surface area are particularly appealing for sensing applications, we further functionalized our nanoporous fibrous membranes with a phosphorescent oxygen-sensitive dye. The hybrid membranes possess high brightness, stability in aqueous medium, linear response to oxygen and hence represent a promising scaffold for cell growth, contactless monitoring of oxygen and live fluorescence imaging in 3-D cell models

Monitoring Spin-Crossover Properties by Diffused Reflectivity

International audienceIn this work we present a detailed study showing the importance of the Kubelka-Munk (KM) correction in the analysis of diffuse reflectivity measurements to characterize spin crossover compounds. Combined reflectance and magnetic susceptibility measurements are carried out as a function of temperature or time to highlight the conditions under which this correction becomes critical. In particular, we investigate the influence of the color contrast between the two spin states on the reflectance measurements. Interestingly, the samples’ contrast seems to play an important role on the spin-like domain structure as suggested by the symmetry of the FORC diagrams. These latest results are discussed within the framework of Classical Preisach model (CPM)

Fabrication and Characterization of Dielectric ZnCr₂O₄ Nanopowders and Thin Films for Parallel-Plate Capacitor Applications

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr2O4 nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr2O4 nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10−4 at a frequency of 1 Hz. Nanoparticulate ZnCr2O4-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process