The rather thin outermost layer of the mammalian skin, stratum corneum (SC), is a complex biomembrane which separates the water rich inside of the body from the dry outside. The skin surface can be exposed to rather extreme variations in ambient conditions (e.g. water activity, temperature and pH), with potential effects on the barrier function. Increased understanding of how the barrier is affected by such changes is highly relevant for regulation of transdermal uptake of exogenous chemicals. In the present study we investigate the effect of hydration and the use of a well-known humectant, urea, on skin barrier ultrastructure by means of confocal Raman microspectroscopy. We also perform dynamic vapor sorption (DVS) microbalance measurements to examine the water uptake capacity of SC pretreated with urea. Based on novel Raman images, constructed from 2D spectral maps, we can distinguish large water inclusions within the skin membrane exceeding the size of fully hydrated corneocytes. We show that these inclusions contain water with spectral properties similar to that of bulk water. The results furthermore show that the ambient water activity has an important impact on the formation of these water inclusions as well as on the hydration profile across the membrane. Urea significantly increases the water uptake when present in skin, as compared to skin without urea, and it promotes formation of larger water inclusions in the tissue. The results confirm that urea can be used as a humectant to increase skin hydration.
Degradation of ABS during repeated processing and accelerated ageing
Two disulfide-containing peptides, barrettides A (1) and B (2), from the cold-water marine sponge Geodia barretti are described. Those 31 amino acid residue long peptides were sequenced using mass spectrometry methods and structurally characterized using NMR spectroscopy. The structure of 1 was confirmed by total synthesis using the solid-phase peptide synthesis approach that was developed. The two peptides were found to differ only at a single position in their sequence. The three-dimensional structure of 1 revealed that these peptides possess a unique fold consisting of a long β-hairpin structure that is cross-braced by two disulfide bonds in a ladder-like arrangement. The peptides are amphipathic in nature with the hydrophobic and charged residues clustered on separate faces of the molecule. The barrettides were found not to inhibit the growth of either Escherichia coli or Staphylococcus aureus but displayed antifouling activity against barnacle larvae (Balanus improvisus) without lethal effects in the concentrations tested. (Figure Presented).
Researchers in natural fibers see opportunities in superhydrophobicity for fabrics or paper. The first challenge with natural fiber is their high hydrophilicity when the second is the perpetual search for water born coating in papermaking. These challenges were overcome by a one pot formulation comprising a latex binder, precipitated calcium carbonate and fatty acids to give their hydrophobicity to pigments 1. In this study, we want to go further by replacing the petro-sourced latex with a new kind of fibers that are cellulose nanofibers (CNF).
Inspired by the Lotus leaf, superhydrophobic surfaces have been a center of interest in the last decade because of their high potential in industry for a variety of applications. It is seen as the next generation of surface for anti-fouling and corrosive retardant in navy industry but also in general anti corrosive materials industry. Now widely studied , mechanisms for manufacturing superhydrophobicity are well understood. Born from the alliance of low surface energy chemistry and physical structuration of surface, superhydrophobic materials give a water contact angle above 150° and a slidding angle below 10°.
A challenge for the next generation marine antifouling (AF) paints is to deliver minimum amounts of biocides to the environment. The candidate AF compound medetomidine is here shown to be released at very low concentrations, ie ng ml(-1) day(-1). Moreover, the release rate of medetomidine differs substantially depending on the formulation of the paint, while inhibition of barnacle settlement is independent of release to the ambient water, ie the paint with the lowest release rate was the most effective in impeding barnacle colonisation. This highlights the critical role of chemical interactions between biocide, paint carrier and the solid/aqueous interface for release rate and AF performance. The results are discussed in the light of differential affinity states of the biocide, predicting AF activity in terms of a high surface affinity and preserved bioavailability. This may offer a general framework for the design of low-release paint systems using biocides for protection against biofouling on marine surfaces.
The thermo-rheological behaviour of bitumen depends largely on its chemical structure and intermolecular microstructures. Bitumen is a complex mixture of organic molecules of different sizes and polarities for which the micro-structural knowledge is still rather incomplete. Knowledge at that level can have great implications for behaviour at a larger scale and will help to optimise the bitumen in its production stage. The present study is focused on understanding the fundamental mechanisms behind the micro-structural phase appearance and the speed or mobility at which they change. To do so, atomic force microscopy was utilised at different temperatures to investigate the phase separation behaviour for four different types of bitumen and co-relate it with the differential scanning calorimetry measurements. Based on the experimental evidences, it was found that the observed phase separation is mainly due to the wax/paraffin fraction presence in bitumen and that the investigated bitumen behaves quite differently. Recommendations are made to continue this research into qualitative information to be used on the asphalt mix design level.
Hydrophobized silica nanoparticles of different sizes, from 16 to 500 nm, were used to impart roughness to a hydrophobic polydimethylsiloxane (PDMS) coating with the aim of obtaining superhydrophobic properties. The particle silanization process and the curing process of the PDMS coating were optimized to increase the contact angle (CA) of the particle containing coating. The evaluation of the coatings, by means of water CA measurements and scanning electron microscopy imaging, shows that superhydrophobicity in the adhesive rose state was achieved using combinations of two differently sized particles, with an excess of the small 16 nm ones. Superhydrophobicity in the lotus state was obtained when the filler concentration of 16 nm particles was 40 wt%, but under such conditions the coating was found to partially crack, which is detrimental in barrier applications. The preference for the rose wetting state can be explained by the round shape of the particles, which promotes the superhydrophobic rose wetting state over that of the superhydrophobic lotus state.
In this study, the time-dependent corrosion protection ability of 10-15. μm thin polydimethylsiloxane-nanoparticle composite coatings was evaluated using mainly open circuit potential and electrochemical impedance spectroscopy measurements. The best result was obtained for the coating containing 20. wt% hydrophobic silica nanoparticles, where it was possible to achieve protection for almost 80 days in 3. wt% NaCl solution. The protective properties offered by this coating are suggested to be due to a synergistic effect of the hydrophobicity of the polydimethylsiloxane matrix and the prolonged diffusion path caused by addition of hydrophobic silica particles.
We report and discuss the corrosion protective properties of a thin nano-composite coating system consisting of an 11μm thick polyester acrylate (PEA) basecoat, covered by an approximately 1-2μm thick layer of TiO2 nanoparticles carrying a 0.05μm thick hexamethyl disiloxane (HMDSO) top coat. The corrosion protective properties were evaluated on carbon steel substrates immersed in 3wt% NaCl solution by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The protective properties of each layer, and of each pair of layers, were also evaluated to gain further understanding of the long-term protective properties offered by the nano-composite coating. The full coating system showed excellent corrosion protective properties in the corrosive environment of 3wt% NaCl-solution for an extended period of 100 days, during which the coating impedance, at the lower frequency limit (0.01Hz), remained above 108 Ωcm2. We suggest that the excellent corrosion protective properties of the complete coating system is due to a combination of (i) good adhesion and stability of the PEA basecoat, (ii) the surface roughness and the elongated diffusion path provided by the addition of TiO2 nanoparticles, and (iii) the low surface energy provided by the HMDSO top coat.
Nanomaterials are small and the small size and corresponding large surface area of nanomaterials confers specific properties, making these materials desirable for various applications, not least in medicine. However, it is pertinent to ask whether size is the only property that matters for the desirable or detrimental effects of nanomaterials? Indeed, it is important to know not only what the material looks like, but also what it is made of, as well as how the material interacts with its biological surroundings. It has been suggested that guidelines should be implemented on the types of information required in terms of physicochemical characterization of nanomaterials for toxicological studies in order to improve the quality and relevance of the published results. This is certainly a key issue, but it is important to keep in mind that material characterization should be fit-for-purpose, that is, the information gathered should be relevant for the end-points being studied.
In biomechanics, a complete understanding of the structures and mechanisms that regulate cellular stiffness at a molecular level remain elusive. In this paper, we have elucidated the role of filamentous actin (F-actin) in regulating elastic and viscous properties of the cytoplasm and the nucleus. Specifically, we performed colloidal-probe atomic force microscopy (AFM) on BjhTERT fibroblast cells incubated with Latrunculin B (LatB), which results in depolymerisation of F-actin, or DMSO control. We found that the treatment with LatB not only reduced cellular stiffness, but also greatly increased the relaxation rate for the cytoplasm in the peripheral region and in the vicinity of the nucleus. We thus conclude that F-actin is a major determinant in not only providing elastic stiffness to the cell, but also in regulating its viscous behaviour. To further investigate the interdependence of different cytoskeletal networks and cell shape, we provided a computational model in a finite element framework. The computational model is based on a split strain energy function of separate cellular constituents, here assumed to be cytoskeletal components, for which a composite strain energy function was defined. We found a significant influence of cell geometry on the predicted mechanical response. Importantly, the relaxation behaviour of the cell can be characterised by a material model with two time constants that have previously been found to predict mechanical behaviour of actin and intermediate filament networks. By merely tuning two effective stiffness parameters, the model predicts experimental results in cells with a partly depolymerised actin cytoskeleton as well as in untreated control. This indicates that actin and intermediate filament networks are instrumental in providing elastic stiffness in response to applied forces, as well as governing the relaxation behaviour over shorter and longer time-scales, respectively.
This report presents the results of the STEM project number 11885-2. The aim of the project was to develop a corrosion test method for metal flue liners with alternating wood and oil burning. Indeed, the conditions gathered by the alternate use of wood and oil for combustion are considered to be severe for metal chimneys, because of the combination of low temperature corrosion (condensation corrosion) involving aggressive ions like chloride, corrosion promoting air pollutants as sulfur dioxide, and high temperature corrosion involving oxidation mechanisms. For the moment there exists no standard method at a European level for the testing of metal flue liners in the conditions named above. Moreover, the combination of oil and wood is becoming more and more common in private houses, especially in northern Europe (mostly Sweden and Finland). The tests performed in this project used partly light oil containing small amounts of sulfur, pellets, and a combination of pellets and light oil that was spiked with determined amounts of chloride and sulfur so that relative high concentrations of chloride and sulfur dioxide were obtained in the flue gas. In none of the six-weeks test performed corrosion could be observed on the metal flue liners of two stainless steels, namely ASTM 304 and 316 (corresponding to SS 2333 and SS 2343). Acceleration was obtained mainly by temperature cycling in that way that condensation corrosion was first initiated. Thereafter the condensate was evaporated and during this process the corrosion promoting contaminants in the condensate increased till the metal flue liner was completely dried. A condensation/drying up cycle lasted for half an hour The proposed test method, apart from having a too low acceleration factor, was found to be difficult to realize with regards to security and handling. Instead of increasing the acceleration factor by varying key parameters, which involves the risk of modifying the corrosion mechanisms compared to real conditions, another method is proposed to be developed in a future work. This unconventional and general method, developed originally by CSTB in France, is based on corrosion by condensate in controlled conditions. The method has shown promising results for some fuels, but needs further development to be used a European standard.