Ref HAL: hal-03036236_v1
DOI: 10.1021/acs.macromol.9b00605
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Taylor dispersion analysis (TDA) is a powerful sizing technique very well suited for (macro)molecules between angstroms and submicrons (typically up to 200 nm). However, new detection modes are required for non-UV-absorbing (macro)molecules such as most of the polysaccharides, including starches. In this work, two different detection modes were compared, backscattering interferometry (BSI) and UV-photooxidation detection (UV-POD). TDA-BSI measures the relative change of the refractive index between eluent and sample (water as eluent in this work), whereas TDA-UV-POD detects the UV-absorbing photo-oxidized products of polysaccharides/starches in strong alkaline media (130 mM NaOH or 1 M KOH). TDA-UV-POD detection was evaluated for linearity and sensitivity at two wavelengths, 214 and 266 nm. The mass-average hydrodynamic radius (Rh) obtained by TDA-BSI and TDA-UV-POD was found to be in excellent agreement, whereas higher average Rh values were obtained by batch dynamic light scattering (DLS) under the same conditions, because of the higher sensitivity of DLS to large-size solutes and aggregates. The hydrodynamic radius distributions obtained by TDA and DLS are intrinsically different but both techniques were found to be complementary, providing useful information on sample dispersity. Owing to the absence of the stationary phase, low sample consumption with straightforward sample preparation (no filtration), and no calibration, TDA is anticipated to become a method of choice for the size-based characterization of polysaccharides, including starches.

Ref HAL: tel-02485748_v1
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Comprendre et soigner les pathologies respiratoires chroniques constituent des enjeux médicaux croissants du fait des modifications de nos modes de vie et de notre environnement. L’épithélium des voies respiratoires assure le rôle de première barrière contre les agressions extérieures grâce à la fonction muco-ciliaire. Les deux éléments fonctionnels de la fonction muco-ciliaire sont la couche de mucus sécrétée par l’épithélium et le battement des cils des cellules ciliées qui contribue à la mise en mouvement de cette couche et à son évacuation des bronches. Le mucus est un fluide complexe et hétérogène et ses propriétés mécaniques couplées aux mécanismes de coordination des cils restent encore mal compris. Mes travaux de thèse ont porté sur une approche biophysique de ces mécanismes. Premièrement, l’étude de la rhéologie du mucus a été menée à deux échelles : en macro-rhéologie de cisaillement et par micro-rhéologie active grâce aux pincettes optiques. Les pincettes optiques permettent également des mesures in situ sur le tissu et des mesures d’adhésion. L’utilisation de la rhéologie comme marqueur des pathologies respiratoires chroniques a été explorée. Deuxièmement, la quantification et la compréhension de la coordination spatiotemporelle de l’activité ciliaire et du transport du mucus engendré ont été conduites, en développant un nouvel outil de traitement d’images de vidéo-microscopie et d’analyse de données.

Ref HAL: hal-02422046_v1
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Hard and soft proteins at fluid interfaces

Ref HAL: hal-02384626_v1
PMID 31774332
DOI: 10.1165/rcmb.2019-0263LE
WoS: 000499728500020
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Ref HAL: hal-02374362_v1
Ref Arxiv: 1812.06484
DOI: 10.1039/c9sm01172b
WoS: WOS:000493519700010
Ref. & Cit.: NASA ADS
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1 Citation
Résumé:

Cells and tissues have the remarkable ability to actively generate the forces required to change theirshape. This active mechanical behavior is largely mediated by the actin cytoskeleton, a crosslinkednetwork of actin filaments that is contracted by myosin motors. Experiments and active gel theorieshave established that the length scale over which gel contraction occurs is governed by a balancebetween molecular motor activity and crosslink density. By contrast, the dynamics that govern thecontractile activity of the cytoskeleton remain poorly understood. Here we investigate the microscopicdynamics of reconstituted actin–myosin networks using simultaneous real-space video microscopy andFourier-space dynamic light scattering. Light scattering reveals different regimes of microscopicdynamics as a function of sample age. We uncover two dynamical precursors that precede macroscopicgel contraction. One is characterized by a progressive acceleration of stress-induced rearrangements,while the other consists of sudden, heterogeneous rearrangements. Intriguingly, our findings suggest aqualitative analogy between self-driven rupture and collapse of active gels and the delayed rupture ofpassive gels observed in earlier studies of colloidal gels under external loads.

Ref HAL: hal-02321405_v1
DOI: 10.1364/AO.58.00G127
WoS: 000502062900019
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In previous work [Opt. Lett. 44, 2827 (2019)], we presented a method based on digital holography and orthogonal matching pursuit, which is able to determine the 3D positions of small objects moving within a larger motionless object. Indeed, if the scattering density is sparse in direct 3D space, compressive sensing algorithms can be used. The method was validated by imaging red blood cell trajectories in the trunk vascular system of a zebrafish (Danio rerio) larva. We give here further details on the reconstruction technique and present a more robust version of the algorithm based on multiple illuminations.

Ref HAL: hal-02311614_v1
Ref Arxiv: 1810.12199
DOI: 10.1007/s10404-019-2195-0
WoS: 000457868900001
Ref. & Cit.: NASA ADS
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3 Citations
Résumé:

Secondary flows are ubiquitous in channel flows, where small velocity components perpendicular to the main velocity appear due to the complexity of the channel geometry and/or that of the flow itself such as from inertial or non-Newtonian effects, etc. We investigate here the inertialess secondary flow of viscoelastic fluids in curved microchan-nels of rectangular cross-section and constant but alternating curvature: the so-called "serpentine channel" geometry. Numerical calculations (Poole et al, 2013) have shown that in this geometry, in the absence of elastic instabilities, a steady secondary flow develops that takes the shape of two counter-rotating vortices in the plane of the channel cross-section. We present the first experimental visualization evidence and characterization of these steady secondary flows, using a complementarity of µPIV in the plane of the channel, and L. Ducloué · L. Casanellas · A. Lindner confocal visualisation of dye-stream transport in the cross-sectional plane. We show that the measured streamlines and the relative velocity magnitude of the secondary flows are in qualitative agreement with the numerical results. In addition to our techniques being broadly applicable to the character-isation of three-dimensional flow structures in microchan-nels, our results are important for understanding the onset of instability in serpentine viscoelastic flows.