2021 Impact factor 1.624
Soft Matter and Biological Physics

EPJ E Topical Issue on Tissue Mechanics

Guest Editors: Alexandre Kabla, Benoît Ladoux & Jean-Marc Di Meglio

This Topical Issue of EPJ E presents a collection of contributions at the cutting edge of research in tissue mechanics.

The rich variety of subjects - epithelia submitted to different mechanical, geometrical or topological constraints, collective and cellular dynamics in cell clusters and organoids, embryology, theory of active motions mediated by topological defects, new methods of analysis – reflects the current intense activity of the biophysics community in this domain. The guest editors hope that these contributions will build a bridge between these fundamental approaches and will present the impact of physical principles on the regulation of biological tissues.

All articles are available here and are freely accessible until 28th January 2023. For further information read the Editorial.

EPJ E Topical Issue on Thermal Non-Equilibrium Phenomena in Fluid Mixtures

When a temperature difference, or gradient, is applied over a bulk fluid mixture at equilibrium, the phenomenon known as thermodiffusion, or the Ludwig-Soret effect, may occur. The thermal force will in general cause the components in the mixture to migrate until the thermal force is balanced by concentration gradients. If the thermal force is applied to a colloidal suspension, the colloids drift towards cold or hot regions. This phenomenon is commonly referred to as thermophoresis. If the fluid is soaked in a porous medium, an additional effect known as thermos-osmosis may occur. Thermo-osmosis leads to a pressure difference. These effects are different from normal diffusion and osmosis, where a concentration difference is the driving force.

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EPJ E Colloquium - Thermophoresis and thermal orientation of Janus nanoparticles in thermal fields

Thermal gradients induce thermodiffusion in aqueous solutions and liquid mixtures and thermophoretic forces that drive the motion of colloids towards hot or cold regions. The Soret coefficient quantifies the strength of the thermophoretic force and varies with temperature, colloid mass and diameter, and colloid-solvent interactions. Janus colloids (JCs ) are nanoparticles with heterogeneous compositions and two contrasting properties, or "two faces" like the Roman god Janus. For example, in spherical JCs, one hemisphere might be hydrophilic and the other hydrophobic. The interest in JCs has grown steadily given their applicability in materials science. While the behaviour of JCs under equilibrium conditions has been explored, their response to thermal gradients is still not fully understood. Explaining the behaviour of JCs in a thermal field might expand their use in materials science and biomedical applications.

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EPJ E Highlight - Considering how friction is maximised when liquids flow on nanoscales

A cross-section of simulations of several different flow types with pistons placed at different positions. Credit: S. Chen et al, 2022

By simulating a liquid confined by a nanoscale structure, researchers discovered the role molecular clogging plays in friction.

The dynamics of how liquids behave when confined in a nanoscale-sized space such as nanochannels, nanotubes or nanopores, is key to understanding a wealth of processes including lubrication, filtration and even energy storage.

The dynamics of liquids at nanoscales are different to behaviour in confinement at macroscales, however. One of the key differences that a reduction in scale creates is friction and shear between the liquid and its solid container. And further complications arise in systems with solid-to-solid contact with features like wear, micro-pitting and scuffing created.

A new paper published in EPJ E and authored by Shan Chen, from the State Key Laboratory of Organic-Inorganic Composites at Beijing University of Chemical Technology, China, uses simulations of molecular dynamics to look at the friction-induced nano-confined liquids.

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EPJ E Colloquium - Predicting thermodiffusion in simple binary fluid mixtures

When a homogeneous mixture is subjected to a thermal gradient, the fluid components are partially separated because of the temperature gradient. This phenomenon, known since the mid-19th century, is called thermodiffusion, the Soret effect or thermophoresis. Despite its relatively small amplitude it impacts many natural systems, such as the salinity gradient in ocean or even pre-biological evolution, and can be exploited in applications ranging from the manipulation of biological macromolecules to isotope enrichment. However, despite numerous attempts by leading researchers, including some Nobel laureates, a full understanding of the microscopic origin of this subtle phenomenon is still lacking and there is no consensus on which model, among the numerous existing ones, is the most reliable to quantify it in dense phases.

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EPJ E Highlight - Modelling the behaviour and dynamics of microswimmers

Clusters of squirmers form in simulations in different numbers and with different torque strengths.

The understanding of the clustering and movement of microswimmers has a range of applications from human health to tackling ecological problems.

Microswimmers are biological entities that range from sperm to phytoplankton to bacteria, meaning that their study can have implications for fields in science as diverse as human health and ecology.

A new paper published in EPJ E looks at the dynamics of microswimmers under gravity. It is authored by a team from the Institute for Theoretical Physics at the Berlin Institute of Technology: Felix Rühle, Arne W. Zantop, and Holger Stark.

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EPJ E Highlight - The relationship between active areas and boundaries with energy input in snapping shells

An image showing the schematics of a nonhomogeneous spherical cap with an active bulk and an active edge.

New research looks at how the geometry of shells relates to the energy input required to actuate snap-through instability.

In nature, diverse organisms such as the hummingbird and Venus flytrap use rapid snapping motions to capture prey, inspiring engineers to create designs that function using snap-through instability of shell structures. Snapping rapidly releases stored elastic energy and does not require a continuously applied stimulus to maintain an inverted shape in bistable structures.

A new paper published in EPJ E authored by Lucia Stein-Montalvo, Department of Civil and Environmental Engineering, Princeton University, and Douglas P. Holmes, Department of Mechanical Engineering, Boston University, along with co-authors Jeong-Ho Lee, Yi Yang, Melanie Landesberg, and Harold S. Park, examines how restricting the active area of the shell boundary allows for a large reduction in its size, and decreases the energy input required to actuate snap-through behaviour in the shell to guide the design of efficient snapping structures.

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EPJE has appointed new Editor-in-Chief Giovanna Fragneto

Giovanna Fragneto

The publishers of European Physical Journal E: Soft Matter and Biological Physics are delighted to announce the appointment of Prof Giovanna Fragneto as Editor-in-Chief, starting January 1 2022. Prof Fragneto has served on the Editorial Board of EPJE since 2011, and takes over the EiC role from Prof François Graner, who steps down at the end of this year.

Prof Fragneto joins Prof Fabrizio Croccolo and Prof Holger Stark as Editors-in-Chief for EPJE, with collective responsibility for papers submitted across the scope of the journal.

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EPJE Topical review - Advances in the study of supercooled water

Water connects to life at many levels, from biology to human activities, health, climate, and technology. And it is the most peculiar simple liquid on our planet. In fact, water presents several anomalies as compared to other simple liquids. These anomalies become more conspicuous at low temperatures within the metastable supercooled regime, that is, the region below its melting point where the stable form is the ordered solid. In this regime water can also exist in the liquid state while at lower temperatures it can also be found in the amorphous (glassy) solid state. In the supercooled state liquid water displays polymorphism displaying both a high density and a low-density structure. The two possible structures that water can choose, and their interplay, are connected with the possible existence of the terminating (critical) point of a line that separates a low-density region from a high-density region and above which the liquid exists in a single phase.

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EPJ E Topical review - Structure and dynamics of nanoconfined water and aqueous solutions

Water, regarded as the matrix of life, is an ubiquitous and peculiar liquid that exhibits a plethora of anomalous properties, both in its stable and metastable bulk states, which fostered a lot of experimental and theoretical studies. Less explored is the field of water and aqueous systems confined in nanoporous materials that, in addition to its fundamental interest, are present in a number of practical situations, including biological and separation processes and energy generation and storage, among others. These facts have triggered a vast amount of research that, so far, has not been conveniently reviewed.

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Editors-in-Chief
F. Croccolo, G. Fragneto and H. Stark
Thanks so much for all the corrections. I am again very grateful to the EPJE production office for the great cooperation and look forward to publishing more in EPJ. Thanks a lot.

Rohit Jain, MPI Biophysical Chemistry, Göttingen, Germany

ISSN (Print Edition): 1292-8941
ISSN (Electronic Edition): 1292-895X

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