HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Bacterial Glass Transition
No full textBacterial assemblies exhibit rich collective behaviors that control their biological functions, making them a relevant object of study from an active matter physics perspective. Dense bacterial suspensions self-organize into distinct physical phases with intriguing dynamical properties. Here, we study dense two-dimensional films of swimming bacteria using advanced imaging techniques and machine learning. By varying density, we uncover a bacterial glass transition, a direct active matter analogue of equilibrium glass transitions in colloidal and molecular fluids. The transition is marked by a dramatic slowdown of dynamics with minimal structural change. Strong dynamic heterogeneity emerges in space and time, leading to an anomalous violation of the Stokes-Einstein relation and a growing dynamic correlation length, universally observed across five bacterial strains. Our results establish that bacterial colonies exhibit glassy dynamics, but their living, active nature gives them unique properties, paving the way for new research regarding how non-equilibrium physics impacts biology
Assessment of microvascular flow in human atherosclerotic carotid plaques using ultrasound localization microscopy
No full textInternational audienc
Contractile forces direct the chiral swirling of minimal cell collectives
No full textInternational audienceChirality is a conserved biological feature with critical implications in tissue morphogenesis and embryonic development. In culture, multicellular groups exhibit spontaneous chiral symmetry break when moving collectively on micropatterned surfaces. Although several studies have shown that actin network integrity and actomyosin network contractility contribute to the establishment of the chirality of the movement, the role of contractile forces to the directionality of the chiral bias in collectives remains to be elucidated. Here, we studied the contractile forces produced by a minimal collective constituted of a pair of endothelial cells. We first show that cell doublets confined on disk-shaped micropatterns undergo spontaneous and persistent chiral swirling, displaying a mild but robust clockwise bias, as the one observed in bigger collectives. This bias could be amplified or reversed by modulating contractile forces. Traction force measurements revealed that high forces tend to drive counterclockwise rotation whereas low forces rather favor a clockwise rotation. Furthermore, the study of heterotypic doublets indicates that the direction of the rotation is determined by the more contractile cells within the doublets. These results thus revealed that contractile leader cells could drive the chiral motion of minimal collectives
Echographie Matricielle Harmonique
No full textUltrasons biomédicaux - Imagerie et caractérisation des tissus mous; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-SonoreNational audienceL’une des hypothèses fondamentales en échographie est de supposer une vitesse du son constante dans le milieu d’intérêt. Cependant, en réalité, les ultrasons traversent différents tissus présentant chacun des vitesses du son bien distinctes. Cette différence entre la véritable distribution de vitesse et un modèle homogène induit des phénomènes d’aberrations qui dégradent significativement la qualité de l’image échographique. L’imagerie matricielle a été développée pour résoudre ce problème. Contrairement au principe d’imagerie confocale utilisé en échographie, l’imagerie matricielle consiste à différencier les points de focalisation en émission et en réception de façon à sonder localement la qualité de focalisation dans le milieu avant de compenser les aberrations associées. A cette fin, l’ensemble des réponses impulsionnelles entre les transducteurs de la sonde ultrasonore est enregistré et stocké sous la forme d’une matrice de réflexion. Du fait de la linéarité de l’équation des ondes, des opérations peuvent lui être appliquées en post-traitement afin de simuler des schémas de focalisation adaptative et ainsi converger vers les lois de focalisations optimales permettant de compenser les aberrations (F.Bureau et al., Nat. Commun. 2023). L’objectif de ce travail est de voir comment cette approche peut être étendue à un mode d’imagerie harmonique, malgré le caractère non-linéaire de ce dernier. En effet, l’échographie harmonique est couramment utilisée par les cliniciens car elle semble offrir un meilleur contraste. La première étape consistera à développer l’imagerie matricielle à partir d’une base d’insonification en ondes focalisées, cette base étant la plus communément utilisée en clinique et la plus adaptée pour générer des non-linéarités. Dans une deuxième étape, nous montrerons comment le formalisme matriciel permet de comprendre les avantages de l’harmonique par rapport au fondamental en ce qu’il permet un meilleur filtrage de la diffusion multiple. Enfin, nous montrerons comment l’imagerie matricielle permet également de compenser les aberrations en régime harmonique
Culture of neuronal spheroids in acoustic levitation and formation of layered cortico-striatal assembloids
No full textThe need to cultivate and analyze three-dimensional multicellular tissues, such as spheroids and organoids, in a reproducible manner has led to the development of new tools and methods to control how they self-organize and differentiate. Here, we present a novel approach based on acoustic levitation for structuring and cultivating layered neurospheres. First, we demonstrate that viable and well-differentiated neuronal spheroids derived from mouse primary neurons can be cultivated under constant acoustic trapping in bulk acoustic wave resonators. We showed that both striatal and cortical cell aggregates formed in acoustic levitation could self-organize into spheroids within 24 hours and remain viable up to 10 days under these particular culture conditions without medium renewal. These spheroids also demonstrated healthy development with typical phenotypic distributions and synaptic maturation. Second, in order to model the cortico-striatal pathway, we succesfully structured and cultivated concentric cortico-striatal assembloids using optimized acoustofluidic chips and specific protocols. These results confirm that acoustic levitation can be used as a new scaffold-free technique for structuring and cultivating complex 3D multicellular objects
Quantitative Mechanochemistry: A Chemical Tool to Bridge Polymer Physics and Mechanics of Soft Polymer Networks
No full textInternational audienceIn recent years, mechanochemistry has imposed itself as a novel promising chemical tool to bridge the gap between polymer physics and continuum mechanics in soft materials. The suitable incorporation of force-sensitive molecules (mechanophores) in load-bearing positions in soft (entropic) polymer networks and in linear chains has provided a tool to detect stresses and bond scission in 2D and 3D through the intensity of an optical signal. We review recent results linking the optical signal detected upon mechanophore activation with the applied mechanical load. Recent investigations have addressed critical questions, such as detecting and quantifying stress fields and measuring quantitative damage by bond scission in diverse cases, including failure in uniaxial tension, crack propagation in continuous loading, cyclic fatigue, or crack initiation in uniaxial and triaxial tension. We also discuss the requirements to go from simple imaging to quantitative detection, enabling comparisons between different materials and the calibration of continuum mechanics models. In ideal cases, the optical signal provides highly sensitive information on the size and intensity of damage zones in front of cracks—regions that would otherwise be undetectable
Spark plasma sintering‐assisted sol‐gel Pechini method: An efficient approach for bulk InGaO 3 (ZnO) m synthesis and texturation
No full textInternational audienceThis article reports on the development of a spark plasma sintering (SPS)‐assisted sol‐gel method for the synthesis of dense pellets, belonging to the series of InGaO 3 (ZnO) m homologous phases, where m is an integer. We show that using this synthesis route, the sintering temperature is significantly decreased down to 950–1000°C as compared to 1150°C using solid‐state synthesis methods, which enables a very good control of the materials stoichiometry by suppressing any cation volatilization. Therefore, dense single‐phase pellets can be obtained for the m values from 1 to 5. However, for larger m values, different layer stackings are observed within single individual crystallites, raising some questions about the thermodynamic stability of InGaO 3 (ZnO) m crystal structure with m > 5. Besides, a significant preferential orientation of the pellets has been observed, linked to the platelet shape of the grains, which can be controlled to some extent by tuning the SPS conditions
PWP measurement of charge distribution in dielectric and conductive liquids under DC electric field
No full textInternational audienceAll liquids exhibit non-zero electrical conductivity, revealing the presence of electric charges. Though often considered uniformly distributed, these charges are influenced by interfaces (electrical double layer) or external electric fields. Their local accumulation can affect the performance of power equipment. Few precise methods exist to measure charge distribution in liquids. The PPRIME Institute has been adapting solid-state techniques, such as the Pressure Wave Propagation (PWP) method, for use in liquids. These have enabled the observation of how charges spatially and temporally reorganize under a DC electric field in dielectric and conductive liquids
Actualités de 2024 en recherche fondamentale
No full textInternational audienceTo present the 2024 basic research retrospective at the sleep congress, four articles were highlighted. The first challenges the notion that sleep facilitates glymphatic clearance of toxins, showing that the diffusion of a fluorescent tracer in the parenchyma does not depend on vigilance state, even though overall clearance decreases during sleep and anesthesia. The second article focuses on a population of Crhbp+ neurons in the SubLateral Dorsal nucleus, which are essential for inducing and maintaining REM sleep; their degeneration has been linked to Parkinson’s disease. A third study finds that activating VGLUT3 neurons in the dorsal raphe reproduces stress-induced sleep disturbances, suppressing REM sleep followed by a rebound. Lastly, one investigation underscores the impact of social context and collective interactions on sleep onset latency and synchronization, suggesting a key role of social environment in regulating sleep.Pour présenter la rétrospective 2024 en recherche fondamentale au congrès du sommeil, quatre articles ont été exposés. Le premier remet en cause l’idée selon laquelle le sommeil faciliterait la clairance glymphatique des toxines, en montrant que la diffusion d’un traceur fluorescent dans le parenchyme ne dépend pas de l’état de vigilance, même si la clairance globale diminue pendant le sommeil et l’anesthésie. Le deuxième porte sur une population de neurones Crhbp+ dans le noyau SubLateral Dorsal, essentielle à l’induction et au maintien du sommeil paradoxal, dont la dégénérescence est associée à la maladie de Parkinson. Un troisième travail révèle que l’activation de neurones VGLUT3 dans le raphé dorsal reproduit les perturbations du sommeil dues au stress, avec suppression du sommeil paradoxal et rebond ultérieur. Enfin, une étude met en évidence l’influence de la socialité et des interactions sociales sur la synchronisation et la latence d’endormissement, suggérant un rôle clé du contexte social dans la régulation du sommeil
Roadmap on machine learning glassy liquids
No full textInternational audienceUnraveling the connections between microscopic structure, emergent physical properties, and slow dynamics has long been a challenge in the field of the glass transition. The absence of clear visible structural order in amorphous configurations complicates the identification of the key features related to structural relaxation and transport properties. The difficulty in sampling equilibrated configurations at low temperatures hampers thorough numerical and theoretical investigations. This roadmap article explores the potential of machine learning (ML) techniques to face these challenges, building on the algorithms that have revolutionized computer vision and image recognition. We present successful ML applications, as well as many open problems for the future, such as transferability and interpretability of ML approaches. We highlight new ideas and directions in which ML could provide breakthroughs to better understand glassy liquids. To foster a collaborative community effort, the article introduces the "GlassBench" dataset, providing simulation data and benchmarks for both two-dimensional and three-dimensional glass-formers. Emphasizing the importance of benchmarks, we identify critical metrics for comparing the performance of emerging ML methodologies, in line with benchmarking practices in image and text recognition. The goal of this roadmap is to provide guidelines for the development of ML techniques in systems displaying slow dynamics, while inspiring new directions to improve our understanding of glassy liquids