Skin Concentrations of Topically Applied Substances in Reconstructed Human Epidermis (RHE) Compared with Human Skin Using in vivo Confocal Raman Microscopy.

Detailed knowledge about the skin concentration of topically applied substances is important to understand their local pharmacological activity. In particular since in vitro models of reconstructed human epidermis are increasingly used as models for diseased skin. In general, diffusion cell experiments are performed to determine the diffusion flux of test substances through either skin models or excised skin both from humans and animals. Local concentrations of the test substances within the skin are then calculated applying diffusion laws and suitable boundary conditions. In this study we used a direct approach to reveal the local concentrations of test substances within skin using confocal Raman microscopy. This non-invasive method can also be applied in vivo and therefore we directly compared in vivo concentrations with those obtained from commercially available reconstructed human epidermis (RHE). Hydrophilic and lipophilic test substances with log Pow from -0.07 to 5.91 were topically applied on human skin in vivo and RHE from SkinEthic was used as the commercial skin model. Local concentration profiles in the stratum corneum (SC) showed substantial differences between the RHE model and the in vivo situation. Differences between RHE models and human skin in vivo were also observed in their molecular composition, in particular in terms of their water profile, lipid content and the presence of natural moisturizing factor (NMF). Confocal Raman is shown to be a powerful non-invasive method for qualitative and quantitative comparative studies between RHE models and human skin in vivo. This method can also be applied to validate RHE models for future use in clinical studies.

Organic thin-film transistors: the passivation of the dielectric-pentacene interface by dipolar self-assembled monolayers.

In organic thin-film transistors (OTFTs), the conducting channel is located near the interface between the organic semiconductor and the oxide dielectric; this interface is crucial for transistor performance. Self-assembled monolayers (SAMs) on the interface reduce the negative influences of the oxide dielectric surface by decreasing the coupling of the carriers at the gate and the role of the active surface defects on transfer. In this paper, we show that SAMs carrying a dipole moment determine the OTFT performance by controlling the charge transfer between the oxide dielectric and the semiconductor. The charges introduced into the semiconductor by this transfer (i.e., residual carriers) lead to a threshold shift to positive values, as well as a decrease in the contact resistance and an increase in the apparent mobility. In this study, other effects of the SAMs, such as the gate potential shift in the channel or a direct reaction between semiconductor and SAM molecules, can be excluded as dominant processes.

The influence of internal length scales on mechanical properties in natural nanocomposites: a comparative study on inner layers of seashells.

Natural materials exhibit outstanding properties compared to their single constituents because of their hierarchical alignment. Therefore, they can be used as a guide to enhance the properties of artificial nanocomposite materials, which eventually could excel compared to their biological counterparts. In this study, seashells of five species with different microstructures were compared by correlating the sizes and aspect ratios of the building blocks to their mechanical behavior. The analyzed nacreous seashells were Trochus maculatus, Haliotis rufescens and Pteria penguin; the non-nacreous seashells were Meretrix lusoria and Pecten maximus. The results were used to determine the optimal values for the shape, size and volume fraction of the structural elements with regards to hardness, Young's modulus and fracture toughness. Surprisingly, the aspect ratio of the mineral phase in all seashells investigated was found to be close to the optimal value for strength as predicted by theory.