Université PSL



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Particle deposition kinetics of colloidal suspensions in microchannels at high ionic strength
Cesare M. Cejas, Fabrice Monti, Marine Truchet, Jean-Pierre Burnouf, and Patrick Tabeling
Langmuir - 33 (26) 6471–6480 - DOI: 10.1021/acs.langmuir.7b01394 - 2017
Despite its considerable practical importance, the deposition of real Brownian particles transported in a channel by a liquid, at small Reynolds numbers, has never been described at a comprehensive level. Here, by coupling microfluidic experiments, theory, and numerics, we succeed in unravelling the problem for the case of straight channels at high salinity. We discover a broad regime of deposition (the van der Waals regime) in which particle–wall van der Waals interactions govern the deposition mechanism. We determine the range of existence of the regime, for which we calculate the concentration profiles, retention profiles, and deposition kinetics analytically. The retention profiles decay as the inverse of the square root of the distance from the entry, and the deposition kinetics are given by the expression , where S is a dimensionless deposition function, A is the Hamaker constant, and ξL is a dimensionless parameter characterizing fluid flow properties. These findings are well supported by numerics. Experimentally, we find that the retention profiles behave as x–0.5±0.1 (where x is the distance from the channel entry) over three decades in scale, as predicted theoretically. By varying the flow conditions (speed, geometry, surface properties, and concentration) so as to cover four decades in ξL and taking the Hamaker constant as a free parameter, we accurately confirm the theoretical expression for the deposition kinetics. Operating in the van der Waals regime enables control of the deposition rates via surface chemistry. From a surface science perspective, working in the van der Waals regime enables us to measure the Hamaker constants of thousands of particles in a few minutes, a task that would take a much longer time to perform with standard AFM.
Nanoscale capillary freezing of ionic liquids confined between metallic interfaces and the role of electronic screening
J. Comtet, A. Niguès, V. Kaiser, B. Coasne, L. Bocquet and A. Siria, Nature Materials
Nature Materials - 16 634‐639 - doi: 10.1038/nmat4880 - 2017
Room-temperature ionic liquids (RTILs) are new materials with fundamental importance for energy storage and active lubrication. They are unusual liquids, which challenge the classical frameworks of electrolytes, whose behaviour at electrified interfaces remains elusive, with exotic responses relevant to their electrochemical activity. Using tuning-fork-based atomic force microscope nanorheological measurements, we explore here the properties of confined RTILs, unveiling a dramatic change of the RTIL towards a solid-like phase below a threshold thickness, pointing to capillary freezing in confinement. This threshold is related to the metallic nature of the confining materials, with more metallic surfaces facilitating freezing. This behaviour is interpreted in terms of the shift of the freezing transition, taking into account the influence of the electronic screening on RTIL wetting of the confining surfaces. Our findings provide fresh views on the properties of confined RTIL with implications for their properties inside nanoporous metallic structures, and suggests applications to tune nanoscale lubrication with phase-changing RTILs, by varying the nature and patterning of the substrate, and application of active polarization.
New avenues for the large scale harvesting of blue energy
A. Siria and L. Bocquet
Nature Chemistry - 1 91 - DOI: 10.1038/s41570-017-0091 - 2017
Salinity gradients have been identified as promising clean, renewable and non-intermittent sources of energy — so-called blue energy. However, the low efficiency of current harvesting technologies is a major limitation for large-scale viability and is mostly due to the low performances of the membrane processes currently in use. Advances in materials fabrication with dedicated chemical properties can resolve this bottleneck and lead to a new class of membranes for blue-energy conversion. In this Perspective, we briefly present current technologies for the conversion of blue energy, describe their performances and note their limitations. We then discuss new avenues for the development of a new class of membranes, combining considerations in nanoscale fluid dynamics and surface chemistry. Finally, we discuss how new functionalities originating from the exotic behaviour of fluids in the nanoscale regime can further boost energy conversion, making osmotic energy a tangible, clean alternative.
Pairwise frictional profile between particles determines discontinuous shear thickening transition in non‐colloidal suspensions
J. Comtet, G. Chatté, A. Niguès, L. Bocquet, A. Siria, and A. Colin
Nat Commun - 8 15633 - DOI: 10.1038/ncomms15633 - 2017
The process by which sheared suspensions go through a dramatic change in viscosity is known as discontinuous shear thickening. Although well-characterized on the macroscale, the microscopic mechanisms at play in this transition are still poorly understood. Here, by developing new experimental procedures based on quartz-tuning fork atomic force microscopy, we measure the pairwise frictional profile between approaching pairs of polyvinyl chloride and cornstarch particles in solvent. We report a clear transition from a low-friction regime, where pairs of particles support a finite normal load, while interacting purely hydrodynamically, to a high-friction regime characterized by hard repulsive contact between the particles and sliding friction. Critically, we show that the normal stress needed to enter the frictional regime at nanoscale matches the critical stress at which shear thickening occurs for macroscopic suspensions. Our experiments bridge nano and macroscales and provide long needed demonstration of the role of frictional forces in discontinuous shear thickening.
Contact dependence and velocity crossover in friction between microscopic solid/solid contacts
McGraw, A. Niguès, A. Chennevière, A. Siria
Nano Lett. - 17 (10) 6335–6339 - DOI: 10.1021/acs.nanolett.7b03076 - 2017
Friction at the nanoscale differs markedly from that between surfaces of macroscopic extent. Characteristically, the velocity dependence of friction between apparent solid/solid contacts can strongly deviate from the classically assumed velocity independence. Here, we show that a nondestructive friction between solid tips with radius on the scale of hundreds of nanometers and solid hydrophobic self-assembled monolayers has a strong velocity dependence. Specifically, using laterally oscillating quartz tuning forks, we observe a linear scaling in the velocity at the lowest accessed velocities, typically hundreds of micrometers per second, crossing over into a logarithmic velocity dependence. This crossover is consistent with a general multicontact friction model that includes thermally activated breaking of the contacts at subnanometric elongation. We find as well a strong dependence of the friction on the dimensions of the frictional probe.
Nano-on-Micro Fibrous Extracellular Matrices for Scalable Expansion of Human Es/Ips Cells
L. Liu, K.-i. Kamei, M. Yoshioka, M. Nakajima, J. Li, N. Fujimoto, S. Terada, Y. Tokunaga, Y. Koyama, H. Sato, K. Hasegawa, N. Nakatsuji and Y. Chen
Biomaterials - 124 47-54 - DOI: 10.1016/j.biomaterials.2017.01.039 - 2017
Human pluripotent stem cells (hPSCs) hold great potential for industrial and clinical applications. Clinical-grade scaffolds and high-quality hPSCs are required for cell expansion as well as easy handling and manipulation of the products. Current hPSC culture methods do not fulfill these requirements because of a lack of proper extracellular matrices (ECMs) and cell culture wares. We developed a layered nano-on-micro fibrous cellular matrix mimicking ECM, named "fiber-on-fiber (FF)" matrix, which enables easy handling and manipulation of cultured cells. While non-woven sheets of cellulose and polyglycolic acid were used as a microfiber layer facilitating mechanical stability, electrospun gelatin nanofibers were crosslinked on the microfiber layer, generating a mesh structure with connected nanofibers facilitating cell adhesion and growth. Our results showed that the FF matrix supports effective hPSC culture with maintenance of their pluripotency and normal chromosomes over two months, as well as effective scaled-up expansion, with fold increases of 54.1 ± 15.6 and 40.4 ± 8.4 in cell number per week for H1 human embryonic stem cells and 253G1 human induced pluripotent stem cells, respectively. This simple approach to mimick the ECM may have important implications after further optimization to generate lineage-specific products.
Efficient laboratory evolution of computationally designed enzymes with low starting activities using fluorescence-activated droplet sorting
Obexer R, Pott M, Zeymer C, Griffiths A, Hilvert D.
Protein Eng Des Sel - 29(9) 355-66 - doi: 10.1093/protein/gzw032 - 2016
De novo biocatalysts with non-natural functionality are accessible by computational enzyme design. The catalytic activities obtained for the initial designs are usually low, but can be optimized significantly by directed evolution. Nevertheless, rate accelerations approaching the level of natural enzymes can only be achieved over many rounds of tedious and time-consuming laboratory evolution. In this work, we show that microfluidic-based screening using fluorescence-activated droplet sorting (FADS) is ideally suited for efficient optimization of designed enzymes with low starting activity, essentially straight out of the computer. We chose the designed retro-aldolase RA95.0, which had been previously evolved by conventional microtiter plate screening, as an example and reoptimized it using the microfluidic-based assay. Our results show that FADS is sufficiently sensitive to detect enzyme activities as low as kcat/Km = 0.5 M(-1)s(-1) The ultra-high throughput of this system makes screening of large mutant libraries possible in which clusters of up to five residues are randomized simultaneously. Thus, combinations of beneficial mutations can be identified directly, leading to large jumps in catalytic activity of up to 80-fold within a single round of evolution. By exploring several evolutionary trajectories in parallel, we identify alternative active site arrangements that exhibit comparably enhanced efficiency but opposite enantioselectivity
Hierarchy and extremes in selections from pools of randomized proteins
Boyer S, Biswas D, Kumar Soshee A, Scaramozzino N, Nizak C2, Rivoire O.
Proc. Nat. Acad. Sci. USA - 113(13) 3482-7 - doi: 10.1073/pnas. - 2016
Variation and selection are the core principles of Darwinian evolution, but quantitatively relating the diversity of a population to its capacity to respond to selection is challenging. Here, we examine this problem at a molecular level in the context of populations of partially randomized proteins selected for binding to well-defined targets. We built several minimal protein libraries, screened them in vitro by phage display, and analyzed their response to selection by high-throughput sequencing. A statistical analysis of the results reveals two main findings. First, libraries with the same sequence diversity but built around different "frameworks" typically have vastly different responses; second, the distribution of responses of the best binders in a library follows a simple scaling law. We show how an elementary probabilistic model based on extreme value theory rationalizes the latter finding. Our results have implications for designing synthetic protein libraries, estimating the density of functional biomolecules in sequence space, characterizing diversity in natural populations, and experimentally investigating evolvability (i.e., the potential for future evolution).
Lineage Tracking for Probing Heritable Phenotypes at Single-Cell Resolution
Denis Cottinet , Florence Condamine, Nicolas Bremond, Andrew D. Griffiths, Paul B. Rainey, J. Arjan G. M. de Visser, Jean Baudry, Jérôme Bibette
Nature Biotechnology - 11(4) e0152395 - doi.org/10.1371/journal.pone.0152395 - 2016
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.
Innate control of actin nucleation determines two distinct migration behaviours in dendritic cells.
Vargas P, Maiuri P, Bretou M, Sáez PJ, Pierobon P, Maurin M, Chabaud M, Lankar D, Obino D, Terriac E, Raab M, Thiam H-R, Brocker T, Kitchen-Goosen SM, Alberts AS, Sunareni P, Xia S, Li R, Voituriez R, Piel M, Lennon-Duménil A-M
Nat. Cell Biol. - 18(1): 43-53 - DOI: 10.1016/j.jim.2015.12.005 - 2016
Dendritic cell (DC) migration in peripheral tissues serves two main functions: antigen sampling by immature DCs, and chemokine-guided migration towards lymphatic vessels (LVs) on maturation. These migratory events determine the efficiency of the adaptive immune response. Their regulation by the core cell locomotion machinery has not been determined. Here, we show that the migration of immature DCs depends on two main actin pools: a RhoA-mDia1-dependent actin pool located at their rear, which facilitates forward locomotion; and a Cdc42-Arp2/3-dependent actin pool present at their front, which limits migration but promotes antigen capture. Following TLR4-MyD88-induced maturation, Arp2/3-dependent actin enrichment at the cell front is markedly reduced. Consequently, mature DCs switch to a faster and more persistent mDia1-dependent locomotion mode that facilitates chemotactic migration to LVs and lymph nodes. Thus, the differential use of actin-nucleating machineries optimizes the migration of immature and mature DCs according to their specific function.

326 publications.