2016 |
Fu, L., Favier, D., Charitat, T., Gauthier, C., & Rubin, A. (2016). A new tribological experimental setup to study confined and sheared monolayers. Review of Scientific Instruments, 87(3).
Abstract: We have developed an original experimental setup, coupling tribology, and velocimetry experiments together with a direct visualization of the contact. The significant interest of the setup is to measure simultaneously the apparent friction coefficient and the velocity of confined layers down to molecular scale. The major challenge of this experimental coupling is to catch information on a nanometer-thick sheared zone confined between a rigid spherical indenter of millimetric radius sliding on a flat surface at constant speed. In order to demonstrate the accuracy of this setup to investigate nanometer-scale sliding layers, we studied a model lipid monolayer deposited on glass slides. It shows that our experimental setup will, therefore, help to highlight the hydrodynamic of such sheared confined layers in lubrication, biolubrication, or friction on solid polymer. (C) 2016 AIP Publishing LLC.
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Guo, Y., Baulin, V. A., & Thalmann, F. (2016). Peroxidised phospholipid bilayers: insight from coarse-grained molecular dynamics simulations. Soft Matter, 12(1), 263–271.
Abstract: An original coarse-grained model for peroxidised phospholipids is presented, based on the MARTINI lipid force field. This model results from a combination of thermodynamic modelling and structural information on the area per lipid, which have been made available recently. The resulting coarse-grained lipid molecules form stable bilayers, and a set of elastic coefficients (compressibility and bending moduli) is obtained. We compare the compressibility coefficient to the experimental values [Weber et al., Soft Matter, 2014, 10, 4241]. Predictions for the mechanical properties, membrane thickness and lateral distribution of hydroperoxide groups in the phospholipid bilayer are presented.
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Hemmerle, A., Fragneto, G., Daillant, J., & Charitat, T. (2016). Reduction in Tension and Stiffening of Lipid Membranes in an Electric Field Revealed by X-Ray Scattering. Phys Rev Lett, 116(22), 228101.
Abstract: The effect of ac electric fields on the elasticity of supported lipid bilayers is investigated at the microscopic level using grazing incidence synchrotron x-ray scattering. A strong decrease in the membrane tension up to 1 mN/m and a dramatic increase of its effective rigidity up to 300 k_{B}T are observed for local electric potentials seen by the membrane less, similar1 V. The experimental results are analyzed using detailed electrokinetic modeling and nonlinear Poisson-Boltzmann theory. Based on a modeling of the electromagnetic stress, which provides an accurate description of the bilayer separation versus pressure curves, we show that the decrease in tension results from the amplification of charge fluctuations on the membrane surface whereas the increase in bending rigidity results from the direct interaction between charges in the electric double layer. These effects eventually lead to a destabilization of the bilayer and vesicle formation. Similar effects are expected at the tens of nanometers length scale in cell membranes with lower tension, and could explain a number of electrically driven processes.
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Micheletto, Y. M. S., Marques, C. M., Silveira, N. P. da, & Schroder, A. P. (2016). Electroformation of Giant Unilamellar Vesicles: Investigating Vesicle Fusion versus Bulge Merging. Langmuir, 32(32), 8123–8130.
Abstract: Partially ordered stacks of phospholipid bilayers on a flat substrate can be obtained by the evaporation of a spread droplet of phospholipid-in-chloroform solution. When exposed to an aqueous buffer, numerous micrometric buds populate the bilayers, grow in size over minutes, and eventually detach, forming the so-called liposomes or vesicles. While observation of vesicle growth from a hydrated lipid film under an optical microscope suggests numerous events of vesicle fusion, there is little experimental evidence for discriminating between merging of connected buds, i.e., a shape transformation that does not imply bilayer fusion and real membrane fusion. Here, we use electroformation to grow giant unilamellar vesicles (GUVs) from a stack of lipids in a buffer containing either (i) nanometric liposomes or (ii) previously prepared GUVs. By combining different fluorescent labels of the lipids in the substrate and in the solution, and by performing a fluorescence analysis of the resulting GUVs, we clearly demonstrate that merging of bulges is the essential pathway for vesicle growth in electroformation.
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Micheletto, Y. M. S., Moro, C. F., Lopes, F. C., Ligabue-Braun, R., Martinelli, A. H. S., Marques, C. M., et al. (2016). Interaction of jack bean (Canavalia ensiformis) urease and a derived peptide with lipid vesicles. Colloids Surf B Biointerfaces, 145, 576–585.
Abstract: Ureases are metalloenzymes that catalyze the hydrolysis of urea to ammonia and carbon dioxide. Jack bean (Canavalia ensiformis) produces three isoforms of urease (Canatoxin, JBU and JBURE-II). Canatoxin and JBU display several biological properties independent of their ureolytic activity, such as neurotoxicity, exocytosis-inducing and pro-inflammatory effects, blood platelets activation, insecticidal and antifungal activities. The Canatoxin entomotoxic activity is mostly due to an internal peptide, named pepcanatox, released upon the hydrolysis of the protein by insect cathepsin-like digestive enzymes. Based on pepcanatox sequence, Jaburetox-2Ec was produced in Escherichia coli. JBU and its peptides were shown to permeabilize membranes through an ion channel-based mechanism. Here we studied the JBU and Jaburetox-2Ec interaction with platelet-like multilamellar liposomes (PML) using Dynamic Light Scattering and Small Angle X-ray Scattering techniques. We also analyzed the interaction of JBU with giant unilamellar vesicles (GUVs) using Fluorescence Microscopy. The interaction of vesicles with JBU led to a slight reduction of hydrodynamic radius, and caused an increase in the lamellar repeat distance of PML, suggesting a membrane disordering effect. In contrast, Jaburetox-2Ec decreased the lamellar repeat distance of PML membranes, while also diminishing their hydrodynamic radius. Fluorescence microscopy showed that the interaction of GUVs with JBU caused membrane perturbation with formation of tethers. In conclusion, JBU can interact with PML, probably by inserting its Jaburetox “domain” into the PML external membrane. Additionally, the interaction of Jaburetox-2Ec affects the vesicle's internal bilayers and hence causes more drastic changes in the PML membrane organization in comparison with JBU.
Keywords: Jaburetox-2Ec; Jack bean urease; Light scattering; Liposomes; Saxs
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2015 |
Aoki, P. H. B., Schroder, A. P., Constantino, C. J. L., & Marques, C. M. (2015). Bioadhesive giant vesicles for monitoring hydroperoxidation in lipid membranes. Soft Matter, 11(30), 5995–5998.
Abstract: Osmotic stresses, protein insertion or lipid oxidation lead to area increase of self-assembled lipid membranes. However, methods to measure membrane expansion are scarce. Challenged by recent progress on the control of phospholipid hydroperoxidation, we introduce a method to quantitatively evaluate membrane area increase based on the bio-adhesion of Giant Unilamellar Vesicles.
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Bauer, M., Kekicheff, P., Iss, J., Fajolles, C., Charitat, T., Daillant, J., et al. (2015). Sliding tethered ligands add topological interactions to the toolbox of ligand-receptor design. Nature Communications, 6.
Abstract: Adhesion in the biological realm is mediated by specific lock-and-key interactions between ligand-receptor pairs. These complementary moieties are ubiquitously anchored to substrates by tethers that control the interaction range and the mobility of the ligands and receptors, thus tuning the kinetics and strength of the binding events. Here we add sliding anchoring to the toolbox of ligand-receptor design by developing a family of tethered ligands for which the spacer can slide at the anchoring point. Our results show that this additional sliding degree of freedom changes the nature of the adhesive contact by extending the spatial range over which binding may sustain a significant force. By introducing sliding tethered ligands with self-regulating length, this work paves the way for the development of versatile and reusable bio-adhesive substrates with potential applications for drug delivery and tissue engineering.
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Gromer, A., Nassar, M., Thalmann, F., Hebraud, P., & Holl, Y. (2015). Simulation of Latex Film Formation Using a Cell Model in Real Space: Vertical Drying. Langmuir, 31(40), 10983–10994.
Abstract: This paper presents a simulation tool applied to latex film formation by drying, a hybrid between a classical numerical resolution method using finite differences and cellular automata, and making use of object-oriented programming. It consists of dividing real space into cells and applying local physical laws to simulate the exchange of matter between neighboring cells. In a first step, the simulation was applied to the simple case of vertical drying of a latex containing only one population of monodisperse particles and water. Our results show how the distribution of latex particles evolves through the different drying stages due to a combination of diffusion, convection, and particle deformation. While repulsive interactions between the particles tend to favor homogeneous distributions in the first drying stage, concentration gradients that develop in opposite ways can be observed depending on the drying regime. The distributions, calculated in various cases, reproduce and extend several theoretical results and are in qualitative agreement with some experimental findings.
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Hemmerle, A., Froehlicher, G., Bergeron, V., Charitat, T., & Farago, J. (2015). Worm-like instability of a vibrated sessile drop. Epl, 111(2).
Abstract: We study the effects of vertical sinusoidal vibrations on a liquid droplet with a low surface tension (ethanol) deposited on a solid substrate. In a precise range of amplitudes and frequencies, the drop exhibits a dramatic worm-like shape instability with a strong symmetry breaking, comparable to the one observed by Pucci et al. (Phys. Rev. Lett., 106 (2011) 024503) on a vibrated floating lens. However, the geometry of our system is much simpler since it does not involve the oscillation and deformation of a liquid-liquid-air contact line. We show that the Faraday waves appearing on the surface of the droplet control its shape and we draw a systematic phase diagram of the instability. A simple theoretical model allows us to derive a relation between the elongation of the droplet and the amplitude of the Faraday wave, in good agreement with measurements of both quantities. Copyright (C) EPLA, 2015
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Korobko, A. V., Marques, C. M., Schoeps, M., Schaelder, V., Wiesner, U., & Mendes, E. (2015). Dielectric discontinuity in equilibrium block copolymer micelles. Soft Matter, 11(36), 7081–7085.
Abstract: The surface tension between the hydrophobic core and the solvent is known to play a major role in the self-assembly of diblock copolymer micelles in solution. Coulombic forces are also very important in the case of aggregates with weakly charged coronas. The aggregation number and morphology are often tuned by the addition of electrolytes to the solution via electrostatic screening and an eventual change in solvent quality. However, when the surface tension is low enough, dielectric discontinuity between the core and the solvent becomes important enough in comparison to other mechanisms, driving the surface tension at the same time it screens electrostatic interactions in the corona. Below, we demonstrate the importance of this effect for micelles with neutral and weakly charged coronas.
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Mukherji, D., Marques, C. M., Stuehn, T., & Kremer, K. (2015). Co-non-solvency: Mean-field polymer theory does not describe polymer collapse transition in a mixture of two competing good solvents. Journal of Chemical Physics, 142(11).
Abstract: Smart polymers are a modern class of polymeric materials that often exhibit unpredictable behavior in mixtures of solvents. One such phenomenon is co-non-solvency. Co-non-solvency occurs when two (perfectly) miscible and competing good solvents, for a given polymer, are mixed together. As a result, the same polymer collapses into a compact globule within intermediate mixing ratios. More interestingly, polymer collapses when the solvent quality remains good and even gets increasingly better by the addition of the better cosolvent. This is a puzzling phenomenon that is driven by strong local concentration fluctuations. Because of the discrete particle based nature of the interactions, Flory-Huggins type mean field arguments become unsuitable. In this work, we extend the analysis of the co-non-solvency effect presented earlier [D. Mukherji et al., Nat. Commun. 5, 4882 (2014)]. We explain why co-non-solvency is a generic phenomenon, which can only be understood by the thermodynamic treatment of the competitive displacement of (co) solvent components. This competition can result in a polymer collapse upon improvement of the solvent quality. Specific chemical details are not required to understand these complex conformational transitions. Therefore, a broad range of polymers are expected to exhibit similar reentrant coil-globule-coil transitions in competing good solvents. (C) 2015 AIP Publishing LLC.
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Weinberger, A., Tanasescu, R., Stefaniu, C., Fedotenko, I. A., Favarger, F., Ishikawa, T., et al. (2015). Bilayer Properties of 1,3-Diamidophospholipids. Langmuir, 31(6), 1879–1884.
Abstract: A series of 1,3-diamido phosphocholines was synthesized, and their potential to form stable bilayers was investigated. Large and giant unilamellar vesicles produced from these new lipids form a wide variety of faceted liposomes. Factors such as cooling rates and the careful choice of the liposome preparation method influence the formation of facets. Interdigitation was hypothesized as a main factor for the stabilization of facets and effectively monitored by small-angle X-ray scattering measurements.
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2014 |
Arranja, A., Schroder, A. P., Schmutz, M., Waton, G., Schosseler, F., & Mendes, E. (2014). Cytotoxicity and internalization of Pluronic micelles stabilized by core cross-linking. Journal of Controlled Release, 196, 87–95.
Abstract: A UV-cross-linkable agent was incorporated and polymerized in Pluronic micelle core to create an interpenetrating polymer network (IPN) of poly(pentaerythritol tetraacrylate). This stabilization prevented micelle disruption below the critical micelle temperature (CMT) and concentration (CMC), while maintaining the integrity of the PEO corona and the hydrophobic properties of the PPO core. The prepared stabilized spherical micelles of Pluronic P94 and F127 presented hydrodynamic diameters ranging from 40 to 50 nm. The stability of cross-linked Pluronic micelles at 37 degrees C in the presence of serum proteins was studied and no aggregation of the micelles was observed, revealing the colloidal stability of the system. Cytotoxicity experiments in NIH/3T3 mouse fibroblasts revealed that the presence of the cross-linking agent did not induce any further toxicity in comparison to the respective pure polymer solutions. Furthermore, stabilized micelles of Pluronic P94 were shown to be less toxic than the polymer itself. A hydrophobic fluorescent probe (Nile red) was absorbed in the cross-linked core of pre-stabilized micelles to mimic the incorporation of a poorly water-soluble drug, and the internalization and intracellular localization of Nile red was studied by confocal microscopy at different incubation times. Overall, the results indicate that Pluronic micelles stabilized by core cross-linking are capable of delivering hydrophobic components physically entrapped in the micelles, thus making them a potential candidate as a delivery platform for imaging or therapy of cancer. (C) 2014 Elsevier B.V. All rights reserved.
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Fallah-Araghi, A., Meguellati, K., Baret, J. - C., El Harrak, A., Mangeat, T., Karplus, M., et al. (2014). Enhanced Chemical Synthesis at Soft Interfaces: A Universal Reaction-Adsorption Mechanism in Microcompartments. Physical Review Letters, 112(2).
Abstract: A bimolecular synthetic reaction (imine synthesis) was performed compartmentalized in micrometer-diameter emulsion droplets. The apparent equilibrium constant (K-eq) and apparent forward rate constant (k(1)) were both inversely proportional to the droplet radius. The results are explained by a noncatalytic reaction-adsorption model in which reactants adsorb to the droplet interface with relatively low binding energies of a few k(B)T, react and diffuse back to the bulk. Reaction thermodynamics is therefore modified by compartmentalization at the mesoscale-without confinement on the molecular scale-leading to a universal mechanism for improving unfavorable reactions.
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Greenall, M. J., & Marques, C. M. (2014). Can adding oil control domain formation in binary amphiphile bilayers? Soft Matter, 10(40), 7925–7931.
Abstract: Bilayers formed of two species of amphiphile of different chain lengths may segregate into thinner and thicker domains composed predominantly of the respective species. Using a coarse-grained mean-field model, we investigate how mixing oil with the amphiphiles affects the structure and thickness of the bilayer at and on either side of the boundary between two neighbouring domains. In particular, we find that oil molecules whose chain length is close to that of the shorter amphiphiles segregate to the thicker domain. This smooths the surface of the hydrophobic bilayer core on this side of the boundary, reducing its area and curvature and their associated free-energy penalties. The smoothing effect is weaker for oil molecules that are shorter or longer than this optimum value: short molecules spread evenly through the bilayer, while long molecules swell the thicker domain, increasing the surface area and curvature of the bilayer core in the interfacial region. Our results show that adding an appropriate oil could make the formation of domain boundaries more or less favourable, raising the possibility of controlling the domain size distribution.
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