HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Magnetic memory and distinct spin populations in ferromagnetic Co 3 Sn 2 S 2
No full textInternational audienceCo3Sn2S2, a ferromagnetic Weyl semi-metal with Co atoms on a kagome lattice, has generated much recent attention. Experiments have identified a temperature scale below the Curie temperature. Here, we find that this magnet keeps a memory, when not exposed to a magnetic field sufficiently large to erase it. We identify the driver of this memory effect as a small secondary population of spins, whose coercive field is significantly larger than that of the majority spins. The shape of the magnetization hysteresis curve has a threshold magnetic field set by the demagnetizing factor. These two field scales set the hitherto unidentified temperature scale, which is not a thermodynamic phase transition, but a crossing point between meta-stable boundaries. Global magnetization is welldefined, even when it is non-uniform, but drastic variations in local magnetization point to a coarse energy landscape, with the thermodynamic limit not achieved at micrometer length scales
Advanced CIGS-mesoporous TiO2 hybrid photocathode functionalized with cobalt quaterpyridine for solar-driven CO₂ reduction
No full textInternational audienceHybrid photocathodes that integrate inorganic semiconductors with molecular catalysts offer a promising strategy for photoelectrochemical CO2 reduction into value-added products. In this work, we present the design and characterization of a high-performance photocathode based on copper indium gallium sulfide (CIGSu), functionalized with a cobalt quaterpyridine (CoQPy) molecular catalyst. The device features a thin (5 nm) TiO2 protective layer deposited by atomic layer deposition (ALD) on CIGSu/CdS, followed by a mesoporous TiO2 layer formed under mild conditions using UV curing and low-temperature annealing (150°C). The mesoporous structure enables high CoQPy loading through chemisorption via phosphonic acid anchoring groups. Under simulated sunlight, the optimized photocathode delivers a photocurrent density of ca. 2 mA/cm² with 95% CO selectivity in carbonate buffer, double the 2 performance of systems using low-porosity TiO2. This work marks progress toward efficient, molecularly functionalized photocathodes for aqueous CO2 reduction
An Engineered Iron-Based MOF for siRNA Delivery Targeting Chemotherapy-Resistant Triple-Negative Breast Cancer
No full textTriple-negative breast cancer (TNBC) remains one of the most aggressive and treatment-resistant malignancies. Herein, we report a glutathione-responsive nanoplatform based on nanoparticles of the mesoporous iron MOF MIL-100(Fe) functionalized with linear polyethyleneimine (LPEI), designed for synergistic chemo/gene/ferroptosis therapy. LPEI imparts enhanced colloidal and chemical stability in physiological media, facilitates lysosomal escape, and enables efficient immobilization and protection of siRNA targeting vimentin (siVIM), a marker of drug resistance and metastasis. Simultaneously, gemcitabine (GEM), a chemotherapeutic agent, is encapsulated within the mesopores of MIL-100. The cationic PEI coating not only improves tumor penetration and phagocytosis evasion but also protects siRNA from nuclease degradation. Upon GSH-triggered MOF degradation in the tumor microenvironment, coordinated release of Fe ions, GEM, and siVIM leads to ferroptosis, S-phase arrest, and vimentin silencing, respectively. This results in 59.6% apoptotic cell death and 74.9% S-phase arrest in TNBC cells. In vivo, the MIL-100@GEM-LPEI@siVIM formulation achieves 84% tumor growth inhibition in a 4T1 murine model, with no observable toxicity. This study presents a multifunctional Fe-MOF-based delivery platform that combines gene silencing, chemotherapy, and ferroptosis to effectively treat triple-negative breast cancer (TNBC), offering a promising preclinical approach to overcoming therapeutic resistance
Strengths and weaknesses of transcranial ultrasound stimulation and its promise in psychiatry: an overview of the technology and a systematic review of the clinical applications
No full textInternational audienceThis article reviews early studies that have demonstrated the ability of low intensity ultrasound waves to modulate brain activity. It also reviews the technological developments that have enabled transcranial ultrasound stimulation (TUS) to achieve millimetric spatial accuracy. This allows precise, noninvasive and reversible brain stimulation, a unique capability when compared to existing techniques such as transcranial magnetic stimulation, transcranial direct-current stimulation, and deep brain stimulation with implanted electrodes. TUS is now technologically ready for clinical translation. As psychiatric disorders have a high prevalence in the general population, and suffer from unmet noninvasive deep brain stimulation clinical needs, this article focuses on the potential application of TUS in psychiatry and reviews recently published clinical proofs of concept that have addressed depression, anxiety, schizophrenia and substance use disorders. Finally, the strengths and weaknesses of TUS technology are discussed, with reference to its clinical translation
Fine-tuning mechanical constraints reveals uncoupled patterning and gene expression programs in murine gastruloids
No full textInternational audienceThe interplay between mechanical forces and genetic programs is fundamental to embryonic development, yet how these factors independently or jointly influence morphogenesis and cell fate decisions remains poorly understood. Here, we fine-tune the mechanical environment of murine gastruloids, three-dimensional in vitro models of early embryogenesis, by embedding them in bioinert hydrogels with precisely tunable stiffness and timing of application. This approach reveals that external constraints can selectively influence transcriptional profiles, patterning, or morphology, depending on the level and timing of mechanical modulation. Gastruloids embedded in ultra-soft hydrogels (< 30 Pa) elongate robustly, preserving both anteroposterior patterning and transcriptional profiles. In contrast, embedding at higher stiffness disrupts polarization while leaving gene expression largely unaffected. Conversely, earlier embedding significantly impacts transcriptional profiles independently of polarization defects, highlighting the uncoupling of patterning and transcription. These findings suggest that distinct cellular states respond differently to external constraints. Live imaging and cell tracking demonstrate that impaired cell motility underlies polarization defects, underscoring the role of mechanical forces in shaping morphogenesis independently of transcriptional changes. By allowing precise control over external mechanical boundaries, our approach provides a powerful platform to dissect how physical and biochemical factors interact to orchestrate early embryonic development
High-entropy Tungsten-Based Oxide as Electrocatalyst and Potential Photo-electro-catalyst for H 2 Evolution
No full textInternational audienceHigh-entropy oxides (HEOx) have emerged as a promising class of materials for photocatalysis due to their unique properties and exceptional stability. This study investigates ( Co 0.2 Ni 0.2 Fe 0.2 Cu 0.2 Zn 0.2 )WO 4 HEOx material synthesized using a top-down approach. The material exhibits a single phase, a suitable band gap for visible light absorption, and a promising electrocatalyst for oxygen evolution reaction (OER) compared to their corresponding individual tungstates. Additionally, the initial tests for Photo-current and MB degradation show the potential for hydrogen (H 2 ) production, making HEOx potential catalysts for solar-driven H 2 generation. ΔS mix = RΣ x n lnx n</div
Droplet Moving On Tilted Pillar Array
No full textInternational audienceSuperhydrophobic behaviour has been described for surfaces that can entrap air at the water/materialinterface. In nature, superhydrophobic (SH) property can be rejuvenated by the synthesis of wax[1] orby soft hairs movements [2]. Synthetic SH materials mainly do not have such a dynamic modulationunless external forces are applied. This is particularly the case of magnetic elastomer pillar arrays thatcan be periodically deformed by the application of a magnetic field [3,4]. Herein, we have explored theinteractions between the contact line of a droplet seated on elastomer pillar arrays in which magneticparticles are embedded. Understanding the low-scale adhesion of this contact line upon pillardeflexion allowed us to drive droplet displacement and positioning on a tilted surface.Complementarily, we can move magnetic droplets on superhydrophobic pillar arrays due to the lowadhesion of the droplet in the Cassie regime[5]. The magnetic droplet has been used to preparemagnetic nanoparticles assemblies in a shorter manner compared to alternative experiments achievedbefore[6]. Magnetically driven materials are definitively excellent platforms for manipulating dropletsas micro-reactors
Dynamics of a bricklayer model: multi-walker realizations of true self-avoiding motion
No full textWe consider a multi-walker generalization of the true self-avoiding walk, the bricklayer model. We perform stochastic simulations and solve the continuum partial differential equations that describe the collective evolution of N bricklayers/walkers. These equations were previously derived from hydrodynamic considerations. In the large-N limit, the results from simulation agree with the solutions of the partial differential equations
Asymétrie de rigidités de flexion pour la programmation de formes
No full textIn this thesis, we investigate how asymmetries in bending stiffness influence the behavior of slender structures under tension. Our main motivation is the study of thin-sheet inflatables made from the soldering of stiff textile sheets for shape-morphing and soft robotics applications. We begin with a brief overview of the state-of-the-art and introduce some experimental and modeling tools.The first part of the manuscrit show that arrays of tubes made from two sheets differing in stiffness exhibit very large curvature upon pressurization. We rationalize these results by modeling the cross-section of a single tube as two coupled bending rods under uniform loading. Our experimental validation of these predictions helps us understand the pressure-dependent geometry of inextensible tubes. Our models reveal a boundary layer at the junction of the thin sheets which determines the curvature of inflatable at high pressures. We also address geometric complexities which arise when the assumptions of slender elasticity are broken and when neighboring tubes come into contact. We then measure the effective bending stiffness of arrays of tubes as they inflate, revealing its nonlinear relationship with pressure.Having characterized the mechanics of stiffness-asymmetric array of tubes, we demonstrate their potential for shape programming. By controlling both tube widths and stiffness asymmetry, we precisely program the curvature of slender, rod-like inflatables. We present several examples of inflatables which adopt complex geometries during pressurization, with examples ranging from origami and kirigami to soft robotic grippers and activated inert structures. We then extend our cross-sectional design to inflatables made of three sheets.In a brief interlude, we present a practical application of thin-sheet inflatables in the context of a design exhibition, which led us to preliminary investigations into the destabilization of geometrically frustrated tubular inflatables.The second part of the manuscrit focuses on minimal objects made of two asymmetric ribbons bound at one end and pulled apart at the other ends. This simplified system clearly exhibits the boundary layer theoretically predicted in thin-sheet inflatables, and is optimal to study it. We characteristic the elastic junction near the bonding as two coupled solutions of Euler’s elastica. While the size of the high curvature area near the junction decreases with the pulling force, we observe the surprising existence of the binding angle as a macroscopic signature of the bending stiffness. Our results thus challenge the standard assumption of neglecting bending stiffness of thin sheets at large tensile loading. In addition, we investigate the rotational response of the structure. Leveraging the independence of the binding angle to the pulling force, we introduce the lambda-test — a visual measurement technique to characterize membranes through simple mechanical coupling. We finally introduce a variation of this system by coupling two ribbons of varying widths along their length. This modification eliminates the self-similarity of the junction layer, making the binding angle dependent on pulling force. We validate the tapered elastica as a model for these ribbons and explore strategies to solve the inverse problem.Dans cette thèse, nous montrons comment les asymétries de rigidité en flexion influencent le comportement des structures élancées sous tension. Notre motivation première est l'étude des structures gonflables à feuilles minces fabriquées à partir de la soudure de feuilles textiles rigides pour des applications de programmation de forme et de robotique molle. Nous commençons par un bref aperçu de l'état de l'art et présentons quelques outils expérimentaux et de modélisation.La première partie du manuscrit démontre que les réseaux de tubes fabriqués à partir de deux feuilles de rigidité différente présentent une courbure très importante lorsque pressurisés. Nous rationalisons ces résultats en modélisant la section d'un tube comme deux tiges de flexion couplées sous chargement uniforme, et validons expérimentalement nos résultats. Nos modèles révèlent l'existence d'une couche limite à la jonction des membranes qui gouverne la courbure du tube gonflable à haute pression. Nous nous penchons également sur les complexités géométriques qui apparaissent lorsque l’hypothèse d’élancement des tubes minces est violée et lorsque des tubes voisins entrent en contact. Nous mesurons ensuite la rigidité de flexion effective d’un réseau de tubes pressurisé, révélant sa relation non-linéaire avec la pression.Après avoir caractérisé la mécanique des réseaux de tubes asymétriques, nous démontrons leur potentiel en matière de programmation de la forme. En contrôlant à la fois la largeur des tubes et l'asymétrie de rigidité, nous programmons avec précision la courbure de structures gonflables élancées, semblables à des rubans. Nous présentons plusieurs exemples de structures gonflables qui adoptent des géométries complexes pendant la pressurisation, avec des exemples allant de l'origami et du kirigami à des pinces robotiques et à des structures inertes activées. Nous étendons ensuite notre conception à des configurations de tubes plus complexes, en particulier à des structures gonflables multicouches.Dans un bref interlude, nous présentons une application pratique des structures gonflables à feuilles minces dans le contexte d'une exposition de design, qui nous a conduits à des recherches préliminaires sur la déstabilisation des structures gonflables tubulaires géométriquement frustrées.La deuxième partie du manuscrit se concentre sur des systèmes minimaux constitués de deux rubans asymétriques liés à une extrémité et mis en tension à l'autre. Ce système simplifié présente la même couche limite prédite théoriquement dans les structures gonflables à feuilles minces, et est optimal pour l'étudier. Nous caractérisons la jonction élastique près de la liaison comme deux solutions couplées de l’elastica d'Euler. Alors que la taille de la zone à forte courbure près de la jonction diminue avec la force de traction, nous observons l'existence surprenante de l'angle de liaison en tant que signature macroscopique de la rigidité de flexion. Nos résultats remettent donc en question l'hypothèse standarde qui consiste à négliger la rigidité de flexion des structures élancées en cas de charge de tension importante. En outre, nous étudions la réponse en rotation de la structure. En tirant parti de l'indépendance de l'angle de liaison par rapport à la force de traction, nous introduisons le lambda-test - une technique de mesure visuelle pour caractériser les membranes par le biais d'un simple couplage mécanique.Enfin, nous introduisons une variante de ce système en couplant deux rubans de largeurs variable selon leur longueur. Cela élimine l'auto-similarité de la couche limite, rendant l'angle de liaison dépendant de la force de traction. Nous validons un modèle pour ces rubans et explorons des stratégies pour résoudre le problème inverse : trouver la forme optimale des rubans pour une fonction objective donnée entre l'angle de liaison et la force de traction
Propriétés de surface, chimie de l’eau de mer et déstabilisation de suspensions microalgales
No full textMicroalgae in seawater form stable bio-colloidal suspensions. Understanding the mechanisms governing their destabilization is essential for optimizing cell harvesting—one of the key steps to insure energy efficient microalgal production. This study investigates the destabilization of microalgal cells in seawater under alkaline conditions. While this phenomenon has been previously observed, an approach at the physical chemistry level is required to elucidate the mechanism driving floc formation. To assess potential cell-cell interactions under these conditions, we developed a dual micropipette assay. However, our findings indicate that the forces measured at high pH arise rather from the mechanical response of inorganic precipitates that preferentially accumulate on the microalgal surface, thereby preventing direct contact between cells. Furthermore, by analyzing the electrophoretic mobility of cells, we were the among the firsts to confirm that microalgae exhibit an electrokinetic behavior characteristic of soft, permeable interfaces. Unlike hard, non-permeable particles, microalgal cells possess a polymeric surface layer that distributes charge within its volume, weakening repulsive interactions from the electric double layer (EDL) compared to classical models. Additionally, we identified, for the first time in microalgal suspensions, two distinct sedimentation behaviors depending on the hydrolysis rate of seawater: (i) individual aggregate settling and (ii) network formation (percolation) leading to collective sedimentation. We define an optimal hydrolysis rate range that promotes rapid sedimentation while minimizing precipitate formation under the conditions studied. These findings provide new insights into microalgal flocculation mechanisms and can contribute to the development of more efficient and sustainable biomass recovery strategies, with potential applications in biofuel production and beyond.Les microalgues en suspension dans leur milieu de culture sont des bio-colloïdes stables dont il faut comprendre les mécanismes de déstabilisation pour optimiser la récolte, l'une des étapes clés dans le bilan énergétique de la production de microalgues. Cette étude examine la déstabilisation des cellules de microalgues en conditions alcalines. Bien que ce phénomène ait déjà été observé, une approche plus physico-chimique est nécessaire pour élucider le mécanisme à l'origine de la formation de flocs. Pour évaluer les interactions potentielles entre cellules dans ces conditions, nous avons développé un essai à double micropipette. Nos résultats montrent cependant que les forces mesurées à pH élevé résultent d'une réponse mécanique des précipités inorganiques qui s'accumulent préférentiellement à la surface des microalgues, empêchant ainsi le contact direct entre les cellules. De plus, en analysant la mobilité électrophorétique des cellules, nous avons été parmi les premiers à envisager que les microalgues puissent présenter un comportement électrocinétique de particules avec des interfaces molles et perméables. Contrairement aux particules rigides et non perméables, les cellules de microalgues possèdent une couche de surface polymérique qui distribue la charge à l'intérieur de son volume, ce qui affaiblit, à charge égale, les interactions répulsives provenant de la couche double électrique (EDL) par rapport aux modèles classiques. Enfin, nous avons identifié pour la première fois sur des supensions algales deux comportements de sédimentation distincts en fonction du taux d'hydrolyse de l'eau de mer: (i) la sédimentation des agrégats individuels et (ii) la formation de réseaux (percolation) menant à une sédimentation collective. Nous définissons une plage optimale de taux d'hydrolyse favorisant une sédimentation rapide tout en minimisant la formation de précipités dans les conditions étudiées. Ces résultats apportent de nouvelles perspectives sur les mécanismes de flocculation des microalgues et peuvent contribuer au développement de stratégies de récupération de biomasse plus efficaces et durables, avec des applications potentielles dans la production de biocarburants