Université PSL



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How do polydisperse repulsive colloids crystallize
Laboratoire Colloïdes et Matériaux Divisés - Robert Botet, Bernard Cabane, Lucas Goehring, Joaquim Lic and Franck Artznerd
Faraday Discuss - 186 229-240 - DOI: 10.1039/C5FD00145E -
A modified version of the Gibbs-ensemble Monte-Carlo method reveals how polydisperse charged colloidal particles can build complex colloidal crystals. It provides general rules that are applicable to this fractionated crystallization that stems from size segregation. It explains the spontaneous formation of complex crystals with very large unit-cells in suspensions of nanoparticles with a broad size distribution.
Hiding in Plain View: Colloidal Self-Assembly from Polydisperse Populations
Laboratoire Colloïdes et Matériaux Divisés - Cabane B, Li J, Artzner F, Botet R, Labbez C, Bareigts G, Sztucki M, Goehring L.
Phys. Rev. Lett. - 116(20) 208001. - doi: 10.1103/PhysRevLett.116.208001 -
We report small-angle x-ray scattering experiments on aqueous dispersions of colloidal silica with a broad monomodal size distribution (polydispersity, 14%; size, 8 nm). Over a range of volume fractions, the silica particles segregate to build first one, then two distinct sets of colloidal crystals. These dispersions thus demonstrate fractional crystallization and multiple-phase (bcc, Laves AB_{2}, liquid) coexistence. Their remarkable ability to build complex crystal structures from a polydisperse population originates from the intermediate-range nature of interparticle forces, and it suggests routes for designing self-assembling colloidal crystals from the bottom up.
Lineage Tracking for Probing Heritable Phenotypes at Single-Cell Resolution
Laboratoire Colloïdes et Matériaux Divisés - Denis Cottinet , Florence Condamine, Nicolas Bremond, Andrew D. Griffiths, Paul B. Rainey, J. Arjan G. M. de Visser, Jean Baudry, Jérôme Bibette
- 11(4): 152395 - https://doi.org/10.1371/journal.pone.0152395 -
Determining the phenotype and genotype of single cells is central to understand microbial evolution. DNA sequencing technologies allow the detection of mutants at high resolution, but similar approaches for phenotypic analyses are still lacking. We show that a drop-based millifluidic system enables the detection of heritable phenotypic changes in evolving bacterial populations. At time intervals, cells were sampled and individually compartmentalized in 100 nL drops. Growth through 15 generations was monitored using a fluorescent protein reporter. Amplification of heritable changes–via growth–over multiple generations yields phenotypically distinct clusters reflecting variation relevant for evolution. To demonstrate the utility of this approach, we follow the evolution of Escherichia coli populations during 30 days of starvation. Phenotypic diversity was observed to rapidly increase upon starvation with the emergence of heritable phenotypes. Mutations corresponding to each phenotypic class were identified by DNA sequencing. This scalable lineage-tracking technology opens the door to large-scale phenotyping methods with special utility for microbiology and microbial population biology.
Digital antimicrobial susceptibility testing usingtheMilliDroptechnology
Laboratoire Colloïdes et Matériaux Divisés - L. Jiang & L. Boitard & P. Broyer & A.-C. Chareire & P. Bourne-Branchu & P. Mahé & M. Tournoud & C. Franceschi & G. Zambardi & J. Baudry & J. Bibette
Eur J Clin Microbiol Infect Dis. - 35(3) 415-22 - doi: 10.1007/s10096-015-2554-z -
We present the MilliDrop Analyzer (MDA), a droplet-based millifluidic system for digital antimicrobial susceptibility testing (D-AST), which enables us to determine minimum inhibitory concentrations (MICs) precisely and accurately. The MilliDrop technology was validated by using resazurin for fluorescence readout, for comparison with standard methodology, and for conducting reproducibility studies. In this first assessment, the susceptibility of a reference Gram-negative strain Escherichia coli ATCC 25922 to gentamicin, chloramphenicol, and nalidixic acid were tested by the MDA, VITEK®2, and broth microdilution as a reference standard. We measured the susceptibility of clinically relevant Gram-positive strains of Staphylococcus aureus to vancomycin, including vancomycin-intermediate S. aureus (VISA), heterogeneous vancomycin-intermediate S. aureus (hVISA), and vancomycin-susceptible S. aureus (VSSA) strains. The MDA provided results which were much more accurate than those of VITEK®2 and standard broth microdilution. The enhanced accuracy enabled us to reliably discriminate between VSSA and hVISA strains.
Equation of state of PEG/PEO in good solvent. Comparison between a one- parameter EOS and experiments
Laboratoire Colloïdes et Matériaux Divisés - Joaquim Li, Martin Turesson, Caroline Anderberg Haglund, Bernard Cabane, Marie Skepö
JPOL - 3861(15) 205-213 - doi:10.1016/j.polymer.2015.10.056 -
We investigate, through osmotic pressure measurements, the validity of the single-parameter equation of state (EOS) for solutions of polyethylene glycols in water, by Cohen et al.1,2 We show that it is physically meaningful and that a reasonable good correspondence between the osmotic pressures for PEG35 in large range of concentrations is obtained. We also take the chain length dependence into account in our analysis, as suggested by Cohen et al. By recalculating the experimental pressures in the paper by Jönsson et al.3 applying the new calibration curve, which is based on the experimental results obtained in this study and the EOS obtained by Cohen et al., there is almost a perfect correspondence between the simulations and the experiments. These results have implications for correctly probing macromolecular interactions in wide range of systems when applying the osmotic stress method.
Nature of flocculation and tactoid formation in montmorillonite: the role of pH
Laboratoire Colloïdes et Matériaux Divisés - M. Segad, T. Åkesson, B. Cabanec and Bo Jönssonb
Phys. Chem. - 17 29608-29615 - DOI: 10.1039/C5CP04007H -
The dissolution and swelling properties of montmorillonite at different pH have been studied, using small angle X-ray scattering (SAXS), imaging and osmotic stress methods combined with Monte Carlo simulations. The acidity of montmorillonite dispersions has been varied as well as the counterions to the net negatively charged platelets. At low pH, Na montmorillonite dissolves and among other species Al3+ is released, hydrated, polymerized and then it replaces the counterions in the clay. This dramatically changes the microstructure of Na montmorillonite, which instead of having fully exfoliated platelets, turns into a structure of aggregated platelets, so-called tactoids. Montmorillonite dispersion still has a significant extra-lamellar swelling among the tactoids due to the presence of very small nanoplatelets.
Filtration of precipitated silica aggregates: Length scales, percolation threshold and yielding behaviour
Laboratoire Colloïdes et Matériaux Divisés - Deka Moussa Ragueh, Martine Meireles, Bernard Cabane, Jérémie Gummel
- vol . 156 (n° 1) 44137 - : http://dx.doi.org/10.1016/j.seppur.2015.10.005 -
Reinforcing precipitated silica systems have a complex hierarchical structure consisting of a branched network made of connected clusters composed of small silica beads welded together into larger dense aggregates. Here, we study the evolution of such structural features during a filtration process. The typical behaviour is that the cakes formed at constant pressure do not reorganize at local scale during a filtration experiment. Accordingly, the creep resistance of a precipitated silica network is high. Overall, there is a percolation threshold, which appears when the branches are pushed into each other. Once this percolation path is reached, the cake withstands compression over more than a decade of applied pressure. Beyond, it seemed useful to make predictions of the filtration properties knowing the typical length scales – small silica beads, dense aggregates, and consolidation behaviour of the cake. A simple approach introducing the concept of an effective medium approximation into Darcy’s law was tested. This approach treats the network as a pseudo-continuum of porous medium built at two main length scales: the size of dense aggregates and a length scale representing the typical distance between the aggregates. The quality of the fit of experimental filtration rates by this simple model indicates that a description based on a continuous network made of two material phases is accurate.
Fast Magnetic Field-Enhanced Linear Colloidal Agglutination Immunoassay
Laboratoire Colloïdes et Matériaux Divisés - Aurélien Daynès, Nevzat Temurok, Jean-Philippe Gineys, Gilles Cauet, Philippe Nerin, Jean Baudry, and Jérôme Bibette
Anal. Chem. - 87 (15) 7583–7587 - DOI: 10.1021/acs.analchem.5b00279 -
We present the principle of a fast magnetic field enhanced colloidal agglutination assay, which is based on the acceleration of the recognition rate between ligands and receptors induced by magnetic forces.1 By applying a homogeneous magnetic field of 20 mT for only 7 s, we detect CRP (C-reactive protein) in human serum at a concentration as low as 1 pM for a total cycle time of about 1 min in a prototype analyzer. Such a short measurement time does not impair the performances of the assay when compared to longer experiments. The concentration range dynamic is shown to cover 3 orders of magnitude. An analytical model of agglutination is also successfully fitting our data obtained with a short magnetic pulse.
The mechanism of eccrine sweat pore plugging by aluminium salts using microfluidics combined with small angle X-ray scattering.
Laboratoire Colloïdes et Matériaux Divisés - Bretagne A, Cotot F, Arnaud-Roux M, Sztucki M, Cabane B, Galey JB.
Soft Matter - 13(20) 3812-3821 - doi: 10.1039/c6sm02510b. -
Aluminium salts are widely used to control sweating for personal hygiene purposes. Their mechanism of action as antiperspirants was previously thought to be a superficial plugging of eccrine sweat pores by the aluminium hydroxide gel. Here we present a microfluidic T junction device that mimics sweat ducts, and is designed for the real time study of interactions between sweat and ACH (Aluminium Chloro Hydrate) under conditions that lead to plug formation. We used this device to image and measure the diffusion of aluminium polycationic species in sweat counter flow. We report the results of small angle X-ray scattering experiments performed to determine the structure and composition of the plug, using BSA (Bovine Serum Albumin) as a model of sweat proteins. Our results show that pore occlusion occurs as a result of the aggregation of sweat proteins by aluminium polycations. Mapping of the device shows that this aggregation is initiated in the T junction at the location where the flow of aluminium polycations joins the flow of BSA. The mechanism involves two stages: (1) a nucleation stage in which aggregates of protein and polycations bind to the wall of the sweat duct and form a tenuous membrane, which extends across the junction; (2) a growth stage in which this membrane collects proteins that are carried by hydrodynamic flow in the sweat channel and polycations that diffuse into this channel. These results could open up perspectives to find new antiperspirant agents with an improved efficacy.
Cell Fate Decision during C. elegans Gonadogenesis
Laboratoire Macromolécules et Microsystèmes en Biologie et Médecine - Michelle A. Wolfgang Keil, Justin M. Benavidez Iva Greenwald
- - DOI:https://doi.org/10.1016/j.cub.2019.07.062 -
Large-Scale Lineage Analysis Refines the Relationship between Birth Order and Cell Fate
The anchor cell (AC) is a unique cell in the proximal region of the developing gonad that serves as the signaling nexus for uterine and vulval patterning and in connecting the uterus and the vulva [12, 13]; its correct specification is therefore critical for maximizing reproductive success. Initially, four cells in the developing somatic primordium have the potential to be the AC (Figure 1A). As described further below, the conserved transcription factor HLH-2 is required to endow these cells with AC potential. The “β cells” soon lose AC potential and always become ventral uterine precursor cells (VUs); the two α cells maintain AC potential and interact via LIN-12/Notch to resolve which will become the AC and which will become another VU

410 publications.