Soft Matter最新文献

This work investigates the calcium-induced formation and properties at the nanoscale of hydrogels of structural extracellular polymeric substances (EPS) extracted from aerobic granular sludge (AGS) during wastewater treatment. By comparing EPS with model polymers representing the key biochemical families present in EPS—alginate for polysaccharides and bovine serum albumin (BSA) for proteins—we aim to elucidate their respective contributions to the overall hydrogel formation with calcium cations. Nanoscale characterization techniques (MP-SPR, QCM-D, and AFM) were employed to assess how divalent cations influence hydrogel formation and properties. Our findings revealed that polysaccharides played a dominant role in hydrogel formation through ionic crosslinking, as well as in hydrogel softness and water retention, while proteins contributed to the modulation of structure and viscoelasticity. The nanoscale structural analysis conducted in this study lays a valuable foundation for further understanding the macroscopic properties of EPS hydrogels, enhancing their potential applications in bio-based materials science.

Correction for ‘Errors matter when measuring Poisson's ratio of nearly incompressible elastomers’ by Robert D. Nedoluha et al., Soft Matter, 2025, 21, 6689–6696, https://doi.org/10.1039/D5SM00535C.

Hydrodynamics is known to have strong effects on the kinetics of phase separation. There exist open questions on how such effects manifest in systems under confinement. Here, we have undertaken extensive studies of the kinetics of phase separation in a two-component fluid that is confined inside pores of cylindrical shape. Using a hydrodynamics-preserving thermostat, we carry out molecular dynamics simulations to obtain results for domain growth and aging for varying temperature and pore width. We find that all systems freeze into a morphology where stripes of regions rich in one or the other component of the mixture coexist. Our analysis suggests that, irrespective of the temperature the growth of the average domain size, ℓ(t), prior to the freezing into stripped patterns, follows the power law ℓ(t) ∼ t^2/3, suggesting an inertial hydrodynamic growth, which typically is applicable for bulk fluids only in the asymptotic limit. Similarly, the aging dynamics, probed by the two-time order-parameter autocorrelation function, also exhibits a temperature-independent power-law scaling with an exponent λ ≃ 2.55, much smaller than what is observed for a bulk fluid.

Polyelectrolyte hydrogels, characterized by their charged networks, exhibit exceptional deformability and biocompatibility, making them ideal platforms for realizing multifunctional and intelligent material systems, yet the molecular origin of their pearl-necklace-like chains remains controversial. Here we develop a thermodynamic unbinding framework that treats the necklace as an assembly of compact polymeric blobs connected by worm-like spacers. The total free-energy density is decomposed into three additive contributions: (i) conformational entropy of the worm-like chains, (ii) electrostatic interaction, and (iii) interfacial unbinding of the blobs, the latter being modeled through a constrained-junction model that captures non-affine micro-deformation. Conceptualizing the pearl necklace as an assembly of distinct polymer blobs and connecting chains, this approach facilitates a detailed examination of its microstructure and complex mechanical response. Closed-form stress–elongation ratio relations are derived for arbitrary three-dimensional loading. The proposed blob-unbinding strategy offers a universal platform for rationalizing the mechanochemistry of polyelectrolyte networks. The uniaxial tensile data of 50 times deformed hyperelastic hydrogels, regular PAM hydrogels, and ring cross-linked hydrogels, and the planar extension data of PTHF hydrogels were analyzed to illustrate the effectiveness of the proposed model.

Investigation of the properties of membrane proteins (MPs) is essential to the successful development of medicines and biotechnology. However, their study is often complicated by denaturation caused by the use of detergents during conventional extraction methods. Copolymers of styrene and maleic acid (SMA) have shown promise in extracting MPs directly from cells while reconstituting lipid membranes into nanodiscs. Despite their potential, there remains a dearth of information on the precise interactions that take place between the copolymers and lipid membranes although they are known to be sensitive to small variations in copolymer composition or structure. We have used reversible addition–fragmentation chain transfer (RAFT) polymerisation to synthesise SMA copolymers with equivalent molar mass, but with inverted block sequences and end group termini. Through a range of experiments, including dynamic light scattering and small-angle neutron scattering (SANS) on SMA aggregates and nanodisc formation studies using UV-vis spectroscopy with both model DMPC lipids and E. coli membranes, the impact of both block distribution and end group chemistry on copolymer–membrane interactions was investigated. It was found that mismatched hydrophilic and hydrophobic end groups on the styrene block and alternating block, respectively, impeded membrane disruption and subsequent solubilisation. This highlights not only how the amphiphilic balance of these blocks is important for efficient nanodisc formation, but also how end groups influence these and may be optimised towards extraction of more challenging MPs. The work contributes to a better understanding of SMA behaviour and offers insight into how these nanomaterials may be better designed and tailored for specific applications.

Topological defects provide a unifying language to describe how orientational order breaks down in active and living matter. Considering cells as elongated particles confluent, epithelial tissues can be interpreted as nematic fields and their defects have been linked to extrusion, migration, and morphogenetic transformations. Yet, epithelial cells are not restricted to nematic order: their irregular shapes can express higher rotational symmetries, giving rise to p-atic order with p > 2. Here we introduce a framework to extract p-atic fields and their defects directly from experimental images. Applying this method to MDCK cells, we find that all symmetries from p = 2 to p = 6 generate defects. Surprisingly, the statistics reveal an even–odd asymmetry, with odd p producing more defects than even p, consistent with geometric frustration arguments based on tilings. In contrast, no strong positional or orientational correlations are found between nematic and hexatic defects, suggesting that different symmetries coexist largely independently. These results demonstrate that epithelial tissues should not be described by nematic order alone, but instead host a spectrum of p-atic symmetries. Our work provides experimental evidence for this multivalency of order and offers a route to test and refine emerging p-atic liquid crystal theories of living matter.

Complex memory effects under applied strain are a defining feature of glassy polymers in the strain hardening regime. We proposed recently a theory for plastic flow and strain hardening as controlled by two contributions to the free energy barriers in glassy polymers submitted to an applied deformation. Free energy barriers decrease under the effect of the stress, which leads to yielding and the onset of plastic flow. Conversely, monomer orientation increases the barriers. These two contributions have very different kinetics. The contribution related to the stress relaxes quickly as a function of the applied stress whereas the orientation contribution relaxes by rotational diffusion, which is very slow at depth in the glassy state. This description could account for the main feature of the Bauschinger effect when considering a stop of the deformation followed by a resuming of the deformation after some waiting time, or for describing deformation cycles, e.g. a tensile test followed by a compression, or the reverse. We show here that the same model allows for interpreting and explaining memory effects in complex deformation histories as regard the distribution of relaxation times, the evolution of tangent delta measured by dielectric spectroscopy and the kinetics of recovery of the reference curve as a function of the waiting time and allows for the interpretation of recent experimental results obtained by small probes reorientation dynamics and dielectric spectroscopy.

The activity of swimming bacteria fundamentally alters the transport properties of passive particles through active agitation. While particle diffusion enhancement is known to scale linearly with the active bacterial flux (the product of swimmer density and velocity), the factors controlling the proportionality coefficient β, which represents the efficiency of energy transfer per swimmer, remain unclear. Here, we systematically investigate how bacterial swimming behavior modulates diffusion enhancement using Escherichia coli and Pseudomonas aeruginosa suspensions. We compare wild-type and smooth-swimming E. coli strains to isolate the effect of tumbling, and we tune swimming velocities in both E. coli and P. aeruginosa to test generality across species with different motility phenotypes. Our results show that bacterial reorientation dynamics have little effect on β, as both wild-type and smooth-swimming E. coli exhibit similar enhancement. In contrast, swimming velocity has a pronounced effect on β in both species. Direct measurements reveal that bacteria-tracer interactions are confined to a radius of approximately 5 µm, with microsphere velocity decaying as r^−1.3 with distance from the nearest bacterium. These findings establish swimming velocity as a key determinant of diffusion enhancement in active suspensions, with implications for understanding nutrient transport and mixing in microbial environments.

The rheology of soft materials is routinely measured at low strain rates to extract constitutive laws necessary for understanding and modeling their behavior. High-frequency rheology, however, remains difficult to access. Consequently, the mechanical properties of soft materials at MHz strain rates are largely unknown. Ultrasound-driven microbubbles, widely used in biomedical imaging, drug delivery, and therapy, act as efficient mechanical actuators at MHz frequencies. Their dynamics depend on nonlinear resonance behavior, the viscoelasticity of their stabilizing shells, and the viscoelastic properties of the surrounding medium. Here, we make use of (nonlinear) bubble dynamics to characterize the rheology of polyacrylamide (PAM) hydrogels at strain rates exceeding 10⁶ s⁻¹. Narrow resonance curves of single coated microbubbles embedded in PAM, obtained through high-speed imaging, were compared to a Rayleigh–Plesset-type model. The results show that the shear modulus is similar in both the Hz and MHz regimes, while the loss modulus behaves very differently, exhibiting an effective shear viscosity at MHz frequencies comparable to that of water. These findings demonstrate a new approach for probing the high-frequency rheology of viscoelastic media.

During interphase, the cell nucleus exhibits spatial compartmentalization between transcriptionally active euchromatin and transcriptionally repressed heterochromatin. In conventional nuclear organization, euchromatin is enriched in the nuclear interior, while heterochromatin - approximately 50% denser - resides near the periphery. The nuclear lamina, a deformable structural shell, further modulates peripheral chromatin organization. Here, we investigate a chromatin model in which an active, crosslinked polymer is tethered to a deformable lamina shell. We show that contractile motor activity, shell deformability, and the spatial distribution of crosslinks jointly determine compartmentalization. Specifically, a radial crosslink density gradient, even with a small increase toward the periphery, coupled with motor activity, drives genomic segregation consistent with experimental observations. This effect arises as motors preferentially draw crosslinks toward the periphery, forming dense domains that promote heterochromatin formation. Our model also predicts increased stiffness of nuclear wrinkles due to heterochromatin compaction beneath the lamina, consistent with instantaneous stiffening observed under nanoindentation. We conclude by outlining potential experimental approaches to validate our model predictions.