HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Oxidative self-polymerization of conjugated biobased free fatty acids produces thick crosslinked polyester films with low surface instabilities
No full textInternational audienceThe ability of polyunsaturated vegetable oils to form solid polymer films by oxygen-induced radical polymerization explains their major role as binders in paints and coatings. However, at large film thicknesses, the diffusion of the oxygen in the bulk is limited which induces gradients of composition and surface instabilities in the film. To avoid this effect, in industrial applications the oil is first prepolymerized, or blown, at high temperature. Here we show that millimeter-thick coatings may be produced by oxidative thermal curing of conjugated polyunsaturated free fatty acids without addition of any catalyst. These free fatty acids (FA) are produced by enzymatic hydrolysis of biobased triglycerides (TG) from Ricinodendron heudelotii oils rich in α-eleostearic acid (18:3). While both the crude oil (TG) and the free fatty acids (FA) are transformed into rubbery polyester networks insoluble in organic solvents, the FA samples show much less surface instabilities. Using infrared spectroscopy and differential scanning calorimetry, we reveal the pathway of the network formation in the TG and FA upon polymerization. By rationalizing these results in comparison with dynamic mechanical analysis of FFA polyesters, we suggest the possible network formation mechanism which may explain lower surface instabilities of the FA samples with respect to the TG ones
Efficient analytical set-up for the monitoring of albumin adduction on Cysteine 34 exposed to mustard agents with optimized digestion and on-line SPE-LC-MS analysis
No full textInternational audienceAdduction of mustard agents such as sulfur mustard (SM), sesquimustard (Q), and nitrogen mustards (HN-1, HN-2, HN-3) on nucleophilic sites of proteins, particularly Cysteine34 of human serum albumin (HSA), can be monitored in plasma to confirm retrospective exposure. The main purpose of this work is to optimize an on-line solid phase extraction (SPE) of HSA tripeptides containing adducted Cys34, coupled to LC-MS. To improve sensitivity of these biomarkers' detection and data robustness the impact of sample preparation steps such as protein precipitation and reduction with dithiothreitol (DTT) prior to digestion with proteinase K (Prot. K) were systematically evaluated. Neither improved digestion efficiency, and at low incubation levels of SM, precipitation even reduced signal intensity. Removing these steps decreased variability and consumable use. Washing conditions were optimized to favour the retention of adducted tripeptides on the SPE sorbent while removing more polar digest compounds. Optimal extraction conditions defined using spiked digests involved washing with 7% (v/v) acetonitrile (ACN) before direct on-line transfer to LC-MS. The optimized method was then applied, as a proof of concept, to plasma incubated with SM and HN-1 at two concentration levels in order to demonstrate its applicability to real biological samples. Limits of quantification (LOQs), determined within this proof-of-concept framework, were established at 10 ng/mL for SM and 40 ng/mL for HN-1 in in vitro adducted plasma
Polymer Vesicle Microreactors Produced using Permeable Polymer Blocks: Circumventing Complex Functionality to Impart Membrane Permeability
No full textInternational audienceThe use of giant vesicles as microreactors presents a novel approach to control biochemical reactions in confined spaces, offering advantages such as compartmentalization, tunable permeability, and potential for biomimetic applications. These constructs can serve as versatile platforms for catalysis, drug delivery, and synthetic biology by providing confined environments that mimic natural cellular compartments. We have successfully produced microvesicles (also referred to as giant vesicles) by means of the simple double emulsification method using five amphiphilic block copolymers comprising poly(ethylene oxide) (PEO) as hydrophilic segment and five disparate hydrophobic blocks: poly(caprolactone) (PCL), poly(methyl methacrylate) (PMMA), poly(lactic acid) (PLA), poly [2-(diisopropylamino)ethyl methacrylate] (PDPA), and poly[2-(heptamethyleneimino)ethyl methacrylate] (PHIA). The last two blocks are pH-responsive (PDPA, PHIA), while the first ones are not (PCL, PMMA, PLA). The resulting vesicles have average size ranging from 2.9 to 9.3 µm, with the pHresponsive vesicles exhibiting larger diameters, likely due to partial protonation of the hydrophobic blocks. The formation of the giant vesicles was confirmed via optical and fluorescence microscopy using Nile red as a hydrophobic marker. The ability of the vesicles to encapsulate larger molecules was demonstrated by loading Alexa-labeled bovine serum albumin (BSA-Alexa). In the step further, the potential of these vesicles as microreactors was explored by encapsulating horseradish peroxidase enzyme (HRP) and evaluating the catalytic oxidation of o-dianisidine in the presence of hydrogen peroxide (H₂O₂), a reaction catalyzed by the HRP enzyme. The experimental evidences highlight that the pH-responsive vesicles are permeable to the reactants, as evidenced by colored product formation, whereas the permeability of the nonresponsive assemblies is reported to be negligible. Truly, the non-responsive vesicles exhibited particularly low permeability, even at the pH where the catalytic activity of the enzyme is optimized. These findings highlight the potential of pH-responsive vesicles for controlled molecular transport and catalytic applications, paving the way for their use in biocatalysis as microreactors
Évolution des génomes et développement (chaire internationale): [résumé des cours et travaux : 2021-2022]
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Physics-Based Learning of the Wave Speed Landscape in Complex Media
No full textWave velocity is a key parameter for imaging complex media, but in vivo measurements are typically limited to reflection geometries, where only backscattered echoes from short-scale heterogeneities are accessible. As a result, conventional reflection imaging fails to recover large-scale variations of the wave velocity landscape. Here we show that matrix imaging overcomes this limitation by exploiting the quality of wave focusing as an intrinsic guide star. We model wave propagation as a trainable multi-layer network that leverages optimization and deep learning tools to infer the wave velocity distribution. We validate this approach through ultrasound experiments on tissue-mimicking phantoms and human breast tissues, demonstrating its potential for tumour detection and characterization. Our method is broadly applicable to any kind of waves and media for which a reflection matrix can be measured
Anisotropic shrinkage and finite strains in confined frictional contacts
No full textInternational audienceWe report on an experimental investigation of the interplay between friction, contact geometry and finite strains for smooth frictional contacts between rigid spherical glass probes and flat silicone substrates. Using both bulk and layered substrates under various loading conditions (normal force, radius of the probe), we show that shear-induced anisotropic shrinkage of the adhesive contact area under steady-state sliding is an effect of finite-elasticity conditions and is drastically affected by the level of geometric confinement. The resulting non-linear coupling between the normal and lateral directions is also investigated by measuring the changes in the indentation depth (conv. normal load) during the stiction of the adhesive contacts under imposed normal load (conv. indentation depth) conditions, with strong effects of contact confinement. From a comparison with adhesiveless linear contact mechanics calculations, we show that the experimental observations can only be accounted for by the occurrence of finite strains/displacements conditions. Accordingly, measurements of the in-plane surface displacements at the surface of the rubber substrates confirm that strain levels well in the neo-Hookean range are experienced during steady-state frictional sliding
Seismic wave interaction with buried cavity networks: Analytical modeling and resonance effects
No full textInternational audienceWe study the scattering of elastic waves by a periodic array of cavities buried in an elastic halfspace. This configuration is relevant in seismology, where shallow voids can locally amplify ground motion. Building on homogenized interface models developed for infinite media, we extend the approach to account for the presence of a stress-free surface. The resulting model yields an analytical solution to the 2D elastodynamic problem for incident longitudinal L and transverse T waves. A semi-analytical multimodal solution is used for validation. The analysis reveals the conditions under which resonances occur in the soil layer between the cavity tops and the surface, with particular emphasis on the low-frequency resonance that dominates in seismic contexts. The model identifies the key parameters governing resonance and provides insights into the transition from infinite to finite cavity arrays. It offers a simplified yet accurate framework for assessing site-specific seismic amplification.</div
Adjusting the Energy Levels of HgTe and InAs Nanocrystals with Alkali Ions
No full textInternational audienceThe photodiode stack is the most effective design geometry for integrating colloidal nanocrystals (NCs) into optoelectronic devices dedicated to light emission and detection. Traditional designs rely on determining the absolute energy band alignment, followed by selecting suitable materials to transport charges (with energy levels resonant to the active material's bands). Because of this method's inherent limitations, we propose to explore an alternative approach where alkali metals are used to tune the absolute energy levels of the optically active layer. We illustrate this concept using lithium and caesium deposition onto narrow band gap NC films (i.e., HgTe and InAs), which are relevant materials for infrared optoelectronics. Our results show that work function shifts up to 0.9 eV can be achieved and that smaller alkalis are more effective at generating this shift. However, different behaviors are observed for HgTe and InAs. In the case of II-VI materials, the alkali acts as a pure dipole (i.e., no shift in the core level), and the film behaves as a bulk effective medium (i.e., no evidence of alkali intercalation). For III-V NCs, the alkali plays a dual role as both a dipole and a redox agent, making the alkali's effect dependent on the film's surface-to-volume ratio and the size of the alkali
Identification of liquid–vapor phase transition using the co-occurrence matrix and Haralick features
No full textInternational audienceIdentification of a phase transition — specifically, the precise timing of the critical temperature crossing — is challenging due to the thermal inertia of the enclosure holding the fluid, the fluid’s finite thermal conductivity, convective flows, and sedimentation. The human eye is particularly well adapted to detecting such phase transitions in images produced by transmitted light through critical fluids. In this study, we used Haralick image features that most closely correspond to human visual perception to identify gas–liquid phase transitions. The images were recorded during the phase transition of sulfur hexafluoride (SF) in microgravity—a particularly challenging scenario.The first goal of this study was to demonstrate that Haralick features can identify a phase transition from recorded images of supercritical fluids in microgravity. While highly sensitive to minute changes in image detail, Haralick features are not inherently normalized; thus, conclusions based on their values for a given image bit depth cannot be reliably compared to those derived from images captured with different cameras or quantization schemes.The second goal of this study was to identify empirical scaling laws for Haralick features that enable the prediction of their behavior as image bit depth varies. Such flexibility would allow direct comparison of results obtained from phase transition datasets recorded using different quantization schemes and imaging systems
Functional ultrasound (fUS) detects mild cerebral alterations using canonical correlation analysis denoising and dynamic functional connectivity analysis
No full textInternational audienceAbstract Functional ultrasound (fUS) is a promising imaging method for evaluating brain function in animals and human neonates. fUS images local cerebral blood volume changes to map brain activity. One application of fUS imaging is the quantification of functional connectivity (FC), which characterizes the strength of the connections between functionally connected brain areas. fUS-FC enables characterization of important cerebral alterations in pathological animal models, with potential for translation into identification of biomarkers of neurodevelopmental disorders. However, the sensitivity of fUS to signal sources other than cerebral activity, such as motion artifacts, cardiac pulsatility, anesthesia (if present), and respiration, limits its capacity to distinguish milder cerebral alterations. Here, we show that using canonical correlation analysis (CCA) preprocessing and dynamic functional connectivity analysis, we can efficiently decouple noise signals from the fUS-FC signal. We use this method to characterize the effects of a mild perinatal inflammation on FC in mice. The inflammation mouse model showed lower occurrence of states of high FC between the cortex, hippocampus, thalamus, and cerebellum as compared with controls, while connectivity states limited either to intracortical connections or to ventral pathways were more often observed in the inflammation model. These important differences could not be distinguished using other preprocessing techniques that we compared, such as global signal regression, highlighting the advantage of canonical correlation analysis for preprocessing fUS data. CCA preprocessing is applicable to a wide variety of fUS imaging experimental situations, from anesthetized to awake animal studies, or for neonatal, perinatal, or neurodevelopmental imaging. Beyond fUS imaging, this method can also be applied to FC data from any neuroimaging modality when the sources of noise can be spatially identified