Soft Matter最新文献

Viscoelastic fluids, such as polymer solutions, surfactant mixtures, colloidal suspensions, emulsions, and biological fluids like blood, are frequently transported in microfluidic systems using external electric fields. In such flows, two distinct types of instabilities can emerge, namely, electro-elastic instabilities (EEI), arising from the interaction between elastic stresses and streamline curvature, and electrokinetic instabilities (EKI), triggered by electrical conductivity gradients once the external electric field exceeds a critical value. Both instabilities can promote fluid mixing by inducing chaotic flow structures; however, their roles are not always complementary. Recent experimental and numerical studies have shown that increasing fluid viscoelasticity can suppress EKI, leading to reduced mixing efficiency in a microfluidic T-junction. However, this study demonstrates that while viscoelasticity initially hinders mixing by damping EKI, a further increase in the Weissenberg number (a measure of fluid elasticity) leads to the onset of EEI, which in turn again increases mixing. Therefore, a non-monotonic relationship between mixing efficiency and Weissenberg number is found in the present study. Furthermore, although both EEI and EKI promote mixing, they differ significantly in their coherent flow structures and regions of origin within the microdevice. To elucidate these differences, we employ the data-driven dynamic mode decomposition (DMD) technique to characterise the underlying instability modes and their influence on the mixing dynamics. Overall, this study provides fundamental insights into how viscoelasticity modulates flow instabilities in electrokinetically driven microflows and offers strategies to optimise mixing by tuning fluid properties and operating conditions.

We investigate the thermodynamic properties of a single inertial probe driven into a nonequilibrium steady state by random collisions with self-propelled active walkers. The probe and walkers are confined within a gravitational harmonic potential. We evaluate the robustness of the effective temperature concept in this active system by comparing values of distinct, independently motivated definitions: a generalized fluctuation–dissipation relation, a kinetic temperature, and via a work fluctuation relation. Our experiments reveal that, under specific conditions, these independent measurements coincide over a wide range of system configurations, yielding a remarkably consistent effective temperature. Furthermore, we also identify regimes where this consistency breaks down, which delineates the fundamental limits of extending equilibrium-like thermodynamic concepts to athermal, actively driven systems.

It is well established that many flagellated bacteria, such as Escherichia coli, swim in clockwise circles above rigid surfaces. However, in a cylindrical microwell with asymmetric top-bottom boundary conditions, such that bacteria segregate into two populations of differing sizes at opposing flat boundaries, the smaller bacterial vortex has been observed to rotate in the opposite direction to that expected in the absence of the other population [K. Beppu, Z. Izri, T. Sato, Y. Yamanishi, Y. Sumino and Y. T. Maeda, Proc. Natl. Acad. Sci. U. S. A., 2021, 118, e2107461118]. Motivated by these observations, we employ flow singularities to investigate the motion of a population of chiral swimmers near one flat boundary of a cylindrical geometry, subject to the flows generated by a bacterial vortex at the opposing surface. We show numerically that, purely due to hydrodynamic interactions, the rotational direction of the bacterial population reverses in the presence of a sufficiently large vortex on the opposite boundary. Our numerical results are fully explained by an analytical theory in the continuum limit, which captures the essential hydrodynamic interactions governing the observed reversal.

Phase separation of a liquid mixture embedded within an elastic network is relevant to a wide range of natural and industrial systems, including biomolecular condensates interacting with the cytoskeleton, structural colouring in bird feathers, and gas bubbles forming within soft sediments. Recent experiments in synthetic polymer gels have demonstrated that when the size of phase-separated domains is comparable to the characteristic pore size of the network, a patterned phase with a well-defined length scale may emerge. Theoretical works based on an equilibrium approach have attributed this pattern formation to non-local elastic effects arising from heterogeneity of the underlying network. Here, we extend these ideas by developing a dynamic theory in which phase separation is coupled to non-local elasticity via the framework of large-deformation poroelasticity. We study our model via both linear stability analysis and numerical simulation, identifying the parameter space in which phase separation occurs, and investigating the impact of different elasticity models. We find that although local elasticity can inhibit phase separation and affect domain count, it is unable to completely suppress coarsening. In contrast, non-local elasticity arrests coarsening to form patterned domains with a well-defined length scale that decreases with increasing stiffness. Our modelling framework thus paves the way for quantitative comparisons between simulations and experiments, for example by considering a strain-stiffening network rheology.

Liquid–liquid phase separation of coarse-grained model polymers of a given length is studied using Langevin dynamics simulations. Some pairs of monomers on each polymer are designated to interact via a short-ranged, effectively monovalent, and relatively strong (SMS) potential. We investigated the effects of the number of SMS interacting pairs, their sequence along the polymers, and polymer flexibility on the phase behavior of the solution, when the remaining monomers are hydrophobic and when they are in a good solvent condition. Our results demonstrate that monomers with SMS interactions can drive phase separation and subsequently gelation of the condensate upon lowering the temperature, even when the remaining monomers are in a good solvent condition. In this case, the phase separation and gelation temperatures increase monotonically with the number of SMS-interacting monomers. Additionally, when the remaining monomers are hydrophobic, the number of SMS monomer pairs and the polymer stiffness exhibit nonmonotonic effects on the phase separation temperature and the surface tension of the condensate. For a fixed number of SMS monomer pairs, their sequence along the polymer chain noticeably influences the phase separation temperature.

Controlling the collective motion of epithelial cell populations is fundamental for understanding multicellular self-organization and for advancing tissue engineering. Under spatial confinement, cells are known to exhibit either vortex rotation or oscillatory motion depending on boundary geometry, but the mechanisms governing transitions between these states remain unclear. Here, we investigate the collective motion of MDCK cells confined within a doublet circular boundary, where the confinement aspect ratio, defined as the distance between the centers of two circles relative to their radius, can be tuned by varying the degree of overlap. When the overlap is large, cells form a stable vortex. Increasing the confinement aspect ratio destabilizes this vortex and induces oscillatory motion characterized by periodic reversals of migration direction, ultimately transitioning into disordered dynamics. To elucidate the underlying mechanism, we developed simulations of self-propelled particles incorporating local alignment (LA) and contact inhibition of locomotion (CIL). The model successfully reproduced the experimentally observed transitions from vortices to oscillatory motion and further revealed that an appropriate balance between LA and CIL is critical for stabilizing vortex pairs with velocity reversals. Our findings demonstrate that the confinement aspect ratio serves as a minimal control parameter governing transitions in the collective dynamics of epithelial monolayers.

Real-time deformability cytometry (RT-DC) enables high-throughput, contact-free mechanical characterization of soft microscopic objects. Here we apply this technique to giant unilamellar vesicles (GUVs). To interpret vesicle deformation in RT-DC, we present a simulation-based model taking into account the area expansion modulus as the dominant mechanical parameter. Using phase-field simulations over a wide parameter space, we find GUV deformation to depend linearly on GUV area. Based on these results, we derive two complementary fitting strategies for extracting the area expansion modulus K from RT-DC data: a direct model-based fit for single-vesicle characterization and a noise-resistant collective approach that enables robust population-level estimates. Furthermore, we introduce a combined fitting method that integrates both approaches to filter outliers and improve accuracy in heterogeneous or noisy datasets. All methods scale across varying flow rates, channel geometries and buffer viscosities, and produce predictions of K consistent with literature values for different lipid compositions. Compared to traditional techniques such as micropipette aspiration, our approach offers orders of magnitude higher throughput without mechanical contact, making it particularly suitable for GUV population studies. Beyond mechanical phenotyping, this framework opens new avenues for sorting vesicle populations based on membrane mechanics, a capability of growing interest in synthetic biology and soft matter research.

This study reports the possibility of employing Zein/Spirulina protein isolate (Zein/SPI) nanocomposite particles as a functional carrier for lipophilic bioactives, using glabridin (GLA) as a model. Zein/SPI nanocomposite particles are synthesized using a conventional anti-solvent precipitation process. The combination of zein and SPI occurs because of electrostatic attraction, hydrophobic interaction, and hydrogen bonding. With an optimal Zein/SPI weight ratio, high encapsulation efficiency and loading capacity of GLA are attained with Zein/SPI nanocomposite particles. GLA is successfully encapsulated in an amorphous form. The presence of SPI improves nanoparticle resilience to aggregation and sedimentation under different environmental conditions. Compared to free GLA, encapsulation enhances GLA stability against ultraviolet light, thermal treatment, and long-term storage. Encapsulated GLA also demonstrates better antioxidant activity than GLA dispersed in water. Additionally, a cytotoxicity study reveals that Zein/SPI nanocomposite particles are highly biocompatible. The in vitro release profile shows a steady and slow release of encapsulated GLA without a burst effect. These results suggest that Zein/SPI nanocomposite particles can be used as all-natural carriers for lipophilic and unstable bioactives in food, pharmaceuticals, and cosmetics.

In manufacturing many natural rubber products, carbon particles and natural rubber chains are mixed by high-intensity processes, such as roll milling and internal mixing. These processes cut natural rubber chains and reduce the performance of the composite. Here we hypothesize that the performance can be enhanced by preserving long chains of natural rubber. We test this hypothesis by mixing carbon particles with natural rubber latex without cutting chains. The long chains are densely entangled and sparsely crosslinked. Above a certain volume fraction, carbon particles percolate. The percolated network of carbon particles and the crosslinked network of rubber chains interpenetrate and form strong noncovalent bonds. Preserving long chains amplifies toughness by more than an order of magnitude, from ∼3.5 kJ m⁻² to ∼63 kJ m⁻², while maintaining modulus. High toughness arises from energy dissipation across multiple length scales: along long rubber strands, across carbon particles, and in a zone of strain-induced crystallization and interfacial dissipation. Modulus is maintained through entanglements of rubber strands and percolation of carbon particles.

Correction for ‘Triggered cell release from shellac–cell composite microcapsules’ by Shwan Abdullah Hamad et al., Soft Matter, 2012, 8, 5069–5077, https://doi.org/10.1039/C2SM07488E.