Aqueous boundary lubrication:Molecular mechanisms, design strategy, and terra incognita

AbstractThe molecular mechanisms for aqueous boundary lubrication are very different from those in the classic boundary lubrication, originating from the fluidity of the hydration shells surrounding the surfactant and lipid headgroups. We discuss the important molecular and structural criteria for effective aqueous boundary lubricants, and highlight the strategy for reinforcing the interfacial structure for aqueous boundary lubrication via synergistic interactions between amphiphilic polymers and lipids/surfactants. It is proposed that the energetic considerations of different molecular elastic deformations in the stalk model of cell membrane fusion can be applied to guide our design of molecular architectures for surfactants and lipids to implement structural integrity in aqueous boundary lubrication. We discuss a controversy associated with the quiescent bilayer structure in the context of boundary lubricant interfacial structures. We also highlight other effective aqueous boundary lubrication systems, including hydrated ions and biomimetic hierarchical constructs inspired by the enigmatic and extremely efficient biological lubrication. Finally, we suggest that the Stribeck curve might be re-considered in light of recent advances in aqueous boundary lubrication, although the exact scope of this new aqueous boundary lubrication regime remains terra incognita

Perfil, hábitos e atitudes do consumidor do presunto de Chaves

Esta comunicação tem por objectivos traçar o perfil do consumidor do Presunto de Chaves; conhecer os seus hábitos, as suas preferências e as suas atitudes; determinar o grau de influência de características, designadamente, pessoais, sociais, geográficas, económicas e contextuais, na decisão de compra deste produto e verificar a existência de diferenças de atitudes e comportamentos entre grupos no que diz respeito ao consumo deste tipo de produto. Esta investigação apoia-se em dados primários obtidos através da aplicação de um questionário a 200 turistas e ou visitantes do concelho de Chaves no período de Julho a Outubro do ano de 2006

Natural and bioinspired nanostructured bactericidal surfaces

Bacterial antibiotic resistance is becoming more widespread due to excessive use of antibiotics in healthcare and agriculture. At the same time the development of new antibiotics has effectively ground to a hold. Chemical modifications of material surfaces have poor long-term performance in preventing bacterial build-up and hence approaches for realising bactericidal action through physical surface topography have become increasingly important in recent years. The complex nature of the bacteria cell wall interactions with nanostructured surfaces represents many challenges while the design of nanostructured bactericidal surfaces is considered. Here we present a brief overview of the bactericidal behaviour of naturally occurring and bio-inspired nanostructured surfaces against different bacteria through the physico-mechanical rupture of the cell wall. Many parameters affect this process including the size, shape, density, rigidity/flexibility and surface chemistry of the surface nanotextures as well as factors such as bacteria specificity (e.g. gram positive and gram negative) and motility. Different fabrication methods for such bactericidal nanostructured surfaces are summarised. (C) 2017 The Authors. Published by Elsevier B.V

Mixed liposomes containing gram-positive bacteria lipids:Lipoteichoic acid (LTA) induced structural changes

Lipoteichoic acid (LTA), a surface associated polymer amphiphile tethered directly to the Gram-positive bacterial cytoplasmic membrane, is a key structural and functional membrane component. Its composition in the membrane is regulated by bacteria under different physiological conditions. How such LTA compositional variations modulate the membrane structural stability and integrity is poorly understood. Here, we have investigated structural changes in mixed liposomes mimicking the lipid composition of Gram-positive bacteria membranes, in which the concentration of Bacillus Subtilis LTA was varied between 0–15 mol%. Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) measurements indicated formation of mixed unilamellar vesicles, presumably stabilized by the negatively charged LTA polyphosphates. The vesicle size increased with the LTA molar concentration up to ∼6.5 mol%, accompanied by a broadened size distribution, and further increasing the LTA concentration led to a decrease in the vesicle size. At 80 °C, SANS analyses showed the formation of larger vesicles with thinner shells. Complementary Cryo-TEM imaging confirmed the vesicle formation and the size increase with LTA addition, as well as the presence of interconnected spherical aggregates of smaller size at higher LTA concentrations. The results are discussed in light of the steric and electrostatic interactions of the bulky LTA molecules with increased chain fluidity at the higher temperature, which affect the molecular packing and interactions, and thus depend on the LTA composition, in the membrane