The European Physical Journal E最新文献

Cells within biological tissue are constantly subjected to dynamic mechanical forces. Measuring the internal stress of tissues has proven crucial for our understanding of the role of mechanical forces in fundamental biological processes like morphogenesis, collective migration, cell division or cell elimination and death. Previously, we have introduced Bayesian inversion stress microscopy (BISM), which is relying on measuring cell-generated traction forces in vitro and has proven particularly useful to measure absolute stresses in confined cell monolayers. We further demonstrate the applicability and robustness of BISM across various experimental settings with different boundary conditions, ranging from confined tissues of arbitrary shape to monolayers composed of different cell types. Importantly, BISM does not require assumptions on cell rheology. Therefore, it can be applied to complex heterogeneous tissues consisting of different cell types, as long as they can be grown on a flat substrate. Finally, we compare BISM to other common stress measurement techniques using a coherent experimental setup, followed by a discussion on its limitations and further perspectives.

In the early 2000s, Long and Lequeux established the first quantitative link between dynamic heterogeneity in the bulk and shifts in the glass transition temperature (T_g) of thin films. Their minimal mean-field model demonstrated that equilibrium density fluctuations give rise to nanometric slow domains, the percolation of which governs vitrification. By showing how geometrical confinement alters this percolation pathway, they predicted (T_g) shifts using only bulk properties, without fitting interfacial parameters. This conceptual breakthrough, in which finite-size effects emerge from projecting bulk dynamic heterogeneity onto a restricted geometry, constitutes the enduring legacy of their work. Subsequent experiments have confirmed this picture, showing that (T_g) depression in free-standing films scales with the thickness of a liquid-like surface layer, while in supported systems mobility gradients reflect the reorganization of slow domains anchored at the interface. Looking forward, I outline at the end of this perspective several possible directions for refining this framework so as to capture a broader spectrum of relaxation channels, thereby enriching our understanding of dynamics in both bulk and confined polymer melts.

Our study provides predictive tools for formulating agri-food products with controlled rheological properties containing mixtures. We investigated the rheological properties of binary biopolymer mixtures composed of xanthan gum (XG) and carboxymethyl cellulose (CMC), with a focus on their synergistic interactions and applications in dysphagia management. Through steady and dynamic rheological tests, we characterized the flow behavior, viscoelastic properties, and thermal stability of XG/CMC blends at varying ratios (100/0 to 0/100). Principal outcomes reveal that XG-rich blends ((ge 70%) XG) exhibit pronounced elastic behavior ((mathrm {G' > G''})), high yield stress, and strong shear-thinning properties, making them suitable for texture-modified foods requiring cohesive bolus formation. In particular, the apparent viscosity at (dot{gamma } = 50~mathrm {s^{-1}})—a critical shear rate for swallowing—was found to be (sim 350~mathrm {mPacdot s}) for pure XG ((1~textrm{wt}%)), classifying it as “honey-like” according to dysphagia standards. Blends with (ge ,70%) of XG maintained viscosities in the nectar-like to honey-like range (51–(1750~mathrm {mPacdot s})), while CMC-rich blends ((mathrm {ge 60%}) CMC) fell below (50~mathrm {mPacdot s}) (“thin”), rendering them unsuitable for dysphagia without reformulation. The Benhadid and Cross models effectively described the rheology of XG- and CMC-rich blends, respectively. Temperature studies highlighted XG’s enhanced thermal stability (20–(30%) viscosity loss at 20–(60,^{circ }textrm{C})) compared to CMC ((>,60%) loss above (30,^{circ }textrm{C})). These results provide predictive tools for designing dysphagia-friendly formulations that balance rheological performance, safety, and sensory acceptability, with XG-dominant blends offering the most promising formulations for meeting IDDSI guidelines.

Effect of temperature and CMC ratio on the apparent viscosity (50 (s^{-1})) of XG/CMC blends, with inset analysis of viscosity and viscoelastic damping factor versus CMC content

Liquid drops slide more slowly over soft, deformable substrates than over rigid solids. This phenomenon can be attributed to the viscoelastic dissipation induced by the moving wetting ridge, which inhibits a rapid motion, and is called “viscoelastic braking”. Experiments on soft dynamical wetting have thus far been modeled using linear theory, assuming small deformations, which captures the essential scaling laws. Quantitatively, however, some important disparities have suggested the importance of large deformations induced by the sliding drops. Here we compute the dissipation occurring below a contact line moving at constant velocity over a viscoelastic substrate, for the first time explicitly accounting for large deformations. It is found that linear theory becomes inaccurate for thin layers and for ridge angles that are typically encountered in experiments. We explore neo-Hookean and strain-stiffening solids and discuss our findings in light of recent experiments.

Maps of the reversible work and the dissipation induced by a contact line moving over a viscoelastic substrate

This paper delves into the intricate relationship between the magnesium nitrogen ((MgN_4))network and its connection to topological indices and the heat of formation. By analyzing a variety of topological indices, we utilize a curve fitting model to predict and clarify the heat of formation—-a vital thermodynamic factor that impacts the stability and reactivity of (MgN_4).Through a detailed correlation analysis, we uncover significant trends and relationships linking the heat of formation with topological indices like the Gutman, Randić, and Zagreb indices. Our findings indicate that the curve fitting model not only yields accurate predictions but also enhances our understanding of the molecular interactions within the (MgN_4) network. Regression techniques will be employed to obtain a curve fitting model, which correlates such indices with experimentally determined heats of formation. These analyses illustrate the accuracy with which thermodynamic properties have been reproduced using the model; it outlines the relevance that topological descriptors have received in computational chemistry so far. By analyzing these results, several insights were obtained into the energetic behavior of magnesium-nitrogen compounds and are pointed out with respect to which role graph-theoretical approaches so far played for the development of material science and chemical engineering.

Evaporative lithography in cells of arbitrary configuration allows for the creation of diverse particle deposition patterns due to the formation of a specific flow structure in the liquid caused by non-uniform evaporation. The latter in turn is determined by the shape of the liquid layer surface and the wetting menisci on the cell walls. Thus, predicting the shape of the wetting menisci can serve as a tool for controlling the process of creating desired particle deposition patterns and evaporation dynamics. Here, we propose a simple and sufficiently accurate methodology for determining the shape of the liquid meniscus in cells of arbitrary geometric shape, based on a combination of mathematical modeling and a series of experimental measurement techniques. The surface profiles of the liquid meniscus in cylindrical, square, and triangular cells were determined by measuring the change in the reflection angle of a laser beam from the free liquid surface while scanning from the cell wall to its center. The height of the wetting meniscus on the inner cell wall and the minimum liquid layer thickness at the center of the cell were measured by analyzing optical images and using a contact method, respectively. 3D meniscus profiles were obtained by numerically solving the Helmholtz equation. The boundary conditions and the unknown constant in the equation were determined based on experimental data obtained for several local points or cross sections. The simulated meniscus shapes showed satisfactory agreement with the experimental local measurements, with a maximum relative error of less than 14%.