Soft Matter

Mechanical properties of biological tissues, driven by passive and active forces, play a vital role in several processes ranging from development to cancer metastasis. However, the dynamical responses of cells in tissues, subject to mechanical deformations such as shear and the associated rheological properties, are not well characterized. Here, we use three-dimensional agent-based models for normal and cancer tissues to investigate their responses to simple shear as a function of cell stiffness and stochastic active forces. In the normal epithelium, with uniform strength of active force, the yield stress as a function of shear rate follows the Herschel-Bulkley form over a range of cell volume fraction. Strikingly, the shear rate dependence and the elasticity-dependent changes in the yield stress fall on master curves upon suitable scaling. To model cancer-like behavior, a certain fraction (Np) of cells was chosen to have enhanced activity and decreased stiffness. As Np increases, the extent of collective cell movement decreases, transitioning from affine (collective) to non-affine (individualistic) movement, a finding that is in accord with imaging experiments. Simulations of a model of a stiff solid tumor, with radius Rs embedded in normal tissue, show that as Rs increases, the yield stress increases. Interestingly, the cells migrate collectively as Rs increases. A Gaussian Mixture Model (GMM) and a mean field theory quantitatively account for the simulation as well as experimental results on cancerous, non-cancerous, and a mixture of these two types. The combined theoretical and experimental study establishes that heterogeneity in stiffness and activity determines non-affine movements in normal and cancer tissues.

Wound repair is an important mechanism to preserve tissue integrity in organisms after injury. However, why different tissues exhibit different mechanisms to repair wounds is a long-standing question that remains unanswered. In this work, we theoretically explore the role of the purse string, an actomyosin contractile cable used by tissues to close small wounds. Does the tissue 3D geometry influence the efficiency of the purse string in driving wound closure? Using a 3D biophysical model, we study in silico tissues with the same cell volumes but different aspect ratios, ranging from squamous to thick and tall tissues. The model predicts that taller cells are easily deformed by the purse string. In contrast, very squamous cells require a very strong purse string that might demand additional cellular mechanisms to close the gap. These findings establish a theoretical framework to predict the optimal biophysical mechanisms of wound healing in different tissues. Graphical abstractCells of different aspect ratios can be observed in a range of organisms with different function and mechanics. The wound healing efficiency of the purse string increases with the cell aspect ratio in our theoretical exploration. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=135 SRC="FIGDIR/small/743165v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@d44ab0org.highwire.dtl.DTLVardef@1737cbaorg.highwire.dtl.DTLVardef@101b5d4org.highwire.dtl.DTLVardef@1487f26_HPS_FORMAT_FIGEXP M_FIG C_FIG

Recent experiments show that protein condensates sitting on opposite surfaces of a flat lipid membrane move together and prefer to overlap, even though they cannot touch each other. This points to an indirect, membrane-mediated interaction. Two mechanisms could be responsible: a curvature-induced interaction, which is energetic in origin, and a fluctuation-induced interaction, which is entropic. Here we study both with coarse-grained molecular dynamics simulations, using Cookes implicit-solvent lipid model together with a generic bead-spring polymer model for the condensate. We compute the potential of mean force between two condensates across the membrane. For condensates of the same size, full overlap is unfavorable, and the pair instead settles into a partially overlapping state that bends the membrane into an S-like shape. When the two condensates differ strongly in size, full overlap becomes favorable. We explain this with a simple geometric picture. The condensate wets the membrane as a thin film and imposes curvature only along its rim, while membrane tension flattens the membrane under its interior. The resulting ring of curvature can trap a smaller condensate on the opposite side. We also compare the bending undulations and the effective bending modulus of a bare membrane, a membrane with one condensate, and a membrane with condensates on both sides. A wetting condensate suppresses the undulation modes and stiffens the membrane, but whether this makes overlap entropically favorable remains inconclusive. Our results indicate that the coupling is driven mainly by curvature, and that it depends on the wetting mechanism and on the membrane tension.

Inefficient endosomal escape is a crucial barrier to intracellular delivery of nucleic acid therapeutics using lipid nanoparticles (LNPs). The use of ionizable lipids (ILs) has significantly improved cargo delivery efficiency, yet the physical basis of their interaction with endosomal membranes and their role in endosomal escape remain unclear. It has been suggested that, as ILs become cationic during endosomal acidification, electrostatic affinity promotes fusion of the LNPs with the endosome. In this paper, we propose an additional mechanism in which ILs are redistributed from LNPs to host membranes, modulating the elastic properties and curvature of the membrane, lowering the energetic threshold for endosome disruption. To test this, we quantified the spontaneous curvature of clinically relevant ILs and ATP-binding lipids and measured the membrane mechanics of giant unilamellar vesicles (GUVs) with an endosome-relevant composition at endosome-relevant pH. Small-angle X-ray scattering (SAXS) measurements reveal that the incorporation of ILs and ATP lipids into endosome-mimetic membranes shifts the spontaneous curvature towards more negative values. Micropipette aspiration experiments indicated a decrease in the apparent area compressibility modulus of membranes doped with ILs and ATP lipids. In addition, membranes showed enhanced fluctuation amplitudes and altered relaxation behavior, consistent with membrane perturbations associated with lipid insertion and pH- or ATP-driven destabilization. Under conditions promoting the partitioning of ILs or ATP-binding lipids, we further observed reduced bending rigidity and increased heterogeneity in membrane tension. Together, these results support a model in which ILs (as well as newly developed ATP-binding lipids) partition into endosomal membranes, softening the membrane and generating local curvature frustration that facilitates endosomal disruption during the natural acidification process. By quantitatively linking lipid composition with changes in membrane elasticity and fluctuation dynamics, this work provides a biophysical framework for understanding how lipid redistribution may contribute to endosomal escape and improve delivery efficiency.

Fingertip friction plays a central role in tactile exploration and object manipulation. During sliding, tangential force depends jointly on the real contact area and the interfacial shear stress, both of which can be influenced by sliding conditions. However, changes in fingertip friction are often interpreted primarily through changes in real contact area, whereas the accompanying changes in interfacial shear stress remain less well characterized. This gap is especially relevant for electrostatic surface haptic displays, which modulate fingertip friction by applying a voltage between the finger and the touch surface. Here, we experimentally quantify the mean interfacial shear stress of a sliding fingertip on an electrostatically actuated touchscreen using simultaneous measurements of tangential force and optically resolved real contact area. Ten participants performed sliding trials across three speeds and three normal forces with and without electrostatic actuation. Interfacial shear stress increased with speed and decreased with normal force; in both cases, these trends arose because real contact area varied more strongly than tangential force. Electrostatic actuation further reduced interfacial shear stress, as increasing voltage produced a larger increase in real contact area than in tangential force. These findings show that interfacial shear stress varies systematically with sliding conditions and electrostatic actuation, clarifying how changes in real contact area and interfacial shear stress combine to shape fingertip-surface friction.

Chronic wounds (principally pressure sores, venous leg ulcers and diabetic foot ulcers) are a drain on global health services and remain a major area of unmet clinical need. Chronic wounds are characterised by a bacterial biofilm (densely aggregated colonies of bacteria encased by a matrix of extracellular polymeric substances), which hinders innate immune response and can prevent wound healing. Bioactive glass (BG) fibres doped with antimicrobial metal ions, such as silver, can offer a promising treatment for chronic wound infections, where silver is well known for its antimicrobial activity against a range of pathogens and is commonly used in wound dressings. We first present a system of non-linear partial differential equations to model the treatment of a chronic wound biofilm infection with BG fibres. The BG fibres are assumed to have two mechanisms of action against the biofilm: physical disruption of the top layers of the biofilm by the BG fibres; and release of antimicrobial silver ions from the BG fibres, which then diffuse into the biofilm and can kill the bacteria. Treatment-associated parameters are estimated from in vitro experimental data using a combination of least-squares minimisation and Approximate Bayesian Computation (ABC). Sensitivity investigations are performed on other parameters that cannot currently be calculated experimentally to investigate their influence on treatment efficacy. We thus predict key parameter regimes that should lead to biofilm eradication, crucially informing the future design of metal-doped BG fibres to maximise treatment efficacy. Author summaryChronic wounds are a huge drain on global health services and will become even more problematic due to an ageing population. Current treatment methods are often unsuccessful, where treatment failure is exacerbated by the presence of a biofilm infection. Biofilms consist of communities of bacteria that adhere to the wound surface and produce extracellular polymeric substances, which can protect the bacteria by acting as both a physical and chemical barrier. More recently, there has been a focus on biofilm-based wound care, where the aim is to firstly eradicate the biofilm infection, which then enables wound healing to occur naturally. Our aim is to produce a novel treatment that can target and eradicate the biofilm infection, followed by directly assisting the wound healing. Bioactive glass (BG) fibres doped with silver offer a promising treatment as they have both anti-biofilm effects and can also stimulate the wound healing process. Here, we restrict attention to their anti-biofilm properties. By developing a mathematical model, we can predict treatment outcomes under several different scenarios, the results of which can then be utilised during design of the BG fibres. Using this combination of computational and experimental approaches, we reduce both the cost and time of optimising this promising treatment.

The rising incidence of invasive fungal diseases emphasizes the need for novel therapeutic strategies, including membrane-targeting antifungal agents, which require representative lipid models for detailed molecular-level studies. In this work, we propose a consensus quinary fungal plasma membrane model based on lipidomic literature data, specifically PC:PE:PI:PA:PS phospholipid model with ratio of 44:29:13:8:6. Using a bottom-up approach, we characterized the biophysical properties of this system - with particular emphasis on mechanical parameters such as bending rigidity and area compressibility - by combining molecular dynamics simulations with experimental flicker-noise and ATR-FTIR spectroscopies. Furthermore, we investigated the effect of two key non-phospholipid components: ergosterol and triacylglycerols. Biophysical analysis revealed that DPPI and its specific interactions with DSPS induced the most substantial deviations in baseline membrane parameters, particularly area per lipid, membrane thickness, and area compressibility, while DSPS influenced bending rigidity change and DLiPA primarily affected lipid packing defects. In addition, ergosterol and TGs were found to influence all of the investigated parameters to different degree. Notably, the overall biophysical profile of the proposed FPMM closely mimicked that of natural vesicles derived from yeast lipid extracts, establishing this model may provide a reliable platform for studying fungal membrane biophysics and lipid-targeting interactions.

Cardiolipin (CL) is a phospholipid found in the inner mitochondrial membrane (IMM) where it increases the efficiency of ATP regeneration. We have investigated the hypothesis that this increase may result in part from CL concentrating H+ at the IMM surface through electrostatic interactions as the CL polar head is a dianion at physiological pH. To this aim, we compared the concentrations and movements of H+ at the surface of giant planar phosphatidylcholine (PC) membranes and 20% CL enriched PC membranes by recording their surface pH with the membrane-grafted pH probe fluorescein DHPE. CL enrichment of the membranes increased their surface H+ activity by a ~4 factor. Moreover, we observed non-gaussian spatial H+ concentration profiles with distance from a point H+ source with both PC and CL membranes suggesting that both lipids also induce interactions between probe molecules. A whole bath pH variation revealed that these interactions allow the traveling of reversible acidification fronts with constant speed over the membrane between high and low pH states. A reaction-diffusion model of these observations suggests that membranes support these fronts through a mechanism of autocatalytic (de)protonation of the membrane surface. In mitochondria, these fronts would result in transitions between high and low pH states, the low one having a larger H+ concentration in CL-enriched regions of the IMM. Such an increase at the inner leaflet of the IMM may increase efficiency of the respiratory chain whereas the increase at the outer leaflet may boost the ATP synthase rate.

Online structural characterization during microfluidic lipid self-assembly is important for understanding and controlling the formation of nonlamellar liquid crystalline nanodispersions. Here, we report a 3D-printed, X-ray-compatible hydrodynamic flow-focusing microfluidic chip with variable channel dimensions, integrated with synchrotron small-angle X-ray scattering (SAXS), for position-resolved SAXS-on-chip monitoring of Ca2+-triggered hexosome formation. Hexosomes were produced under continuous flow by mixing ethanolic solutions of docosahexaenoic acid monoglyceride (MAG-DHA), the negatively charged phosphatidylglycerol DOPG, and -tocopherol with Ca2+-containing PIPES buffer. Online SAXS-on-chip measurements detected three Bragg reflections characteristic of the internal inverse hexagonal (H2) phase on a tens-of-milliseconds residence-time scale, revealing rapid structural evolution during microfluidic mixing. Complementary ex situ SAXS identified the DOPG/Ca2+ molar ratio as a key parameter modulating the direct vesicle-to-hexosome transformation and the compactness of the internal H2 nanostructures. Dynamic light scattering showed that the flow-rate ratio modulated nanoparticle size, yielding hexosomes with mean hydrodynamic diameters in the range of approximately 120-175 nm and polydispersity index values down to 0.14 at a total flow rate of 200 {micro}L min-1. Cryo-TEM revealed coexistence of hexosomes and vesicular nanostructures, highlighting morphological heterogeneity, while Coarse-Grained Molecular Dynamics simulations supported a central role of Ca2+-DOPG association in promoting a direct lamellar-H2 phase transition. Overall, this work shows that 3D-printed SAXS-compatible microfluidics can integrate continuous production with online structural characterization, providing a basis for future formulation and process optimization of drug-loaded cubosomes, hexosomes, and related nonlamellar liquid crystalline nanodispersions.

Tumor spheroid mechanics arise from both the mechanical properties of individual cells and the adhesive interactions that organize them into tissues. The relative contribution of these two factors to the bulk mechanical behavior, however, remains difficult to disentangle experimentally. Here, we develop a computational model of micropipette aspiration to compare the mechanical response of isolated cells and multicellular spheroids within a common computational framework. By independently varying single-cell stiffness and cell-cell adhesion, we quantify their effects on aspiration dynamics, effective elastic modulus, and viscoelastic relaxation. Our results show that increasing single-cell stiffness substantially alters the mechanics of isolated cells but has limited influence on the effective elastic modulus of multicellular spheroids. In contrast, changes in cell-cell adhesion produce pronounced effects on spheroid effective elastic modulus. Nevertheless, both parameters increase the retardation time governing the transition from the initial elastic response to long-time viscous deformation. These findings suggest that multicellular elasticity is governed primarily by intercellular mechanical coupling, whereas the dynamical response to applied stress depends jointly on cell-scale mechanics and cell-cell adhesion.

1.Surface functionality and pH play a decisive role in governing the structural dynamics, hydration, and drug-binding behaviour of dendrimers. Here, all-atom molecular dynamics (MD) simulations were performed on five generations of PAMAM (G1-G5) and PETIM (G2-G6) dendrimers with O-core and N-core architectures, functionalized with amine, carboxylic acid, or sugar terminal groups under different protonation states. Protonation of the tertiary branch-point amines expands the dendrimer structure, increases internal porosity and hydration, and enhances structural fluctuations across both families. In contrast, non-protonated amine -NH2 (NP) and carboxylic acid -COOH (NP) terminated dendrimers, together with deprotonated carboxylate-COO- (DeP) systems, retain comparatively compact conformations. Sugar-functionalized dendrimers ({beta}-galactose-terminated PETIM and D-glucose-terminated PAMAM) are most hydrated and structurally rigid, whereas amine-terminated dendrimers exhibit the greatest conformational dynamics. PAMAM dendrimers with -NH2, -NH3+, and -COO- terminal groups are generally more hydrated than their PETIM counterparts. However, {beta}-galactose-terminated PETIM dendrimers are more hydrophilic than D-glucose-terminated PAMAM dendrimers. N-core PETIM dendrimers also adopt more compact and spherical conformations than equivalent O-core PETIM dendrimers. Drug-binding MD simulations show that curcumin binding is dominated by van der Waals (vdW) interactions, whereas doxorubicin complexation is primarily driven by electrostatic interactions. Among the investigated surface functionalities, -NH2 (NP), -NH3+ (P), -COOH (NP), and -COO- (DeP) terminations exhibit the most favourable drug-binding characteristics. Except for deprotonated carboxylate systems, curcumin binds more strongly than doxorubicin. Overall, these findings establish molecular-level relationships between surface functionality, protonation state, dendrimer architecture, and drug-binding behaviour, providing design principles for pH-responsive dendrimer nanocarriers with enhanced drug-loading and controlled-release performance. TOC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=75 SRC="FIGDIR/small/742721v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@119bf29org.highwire.dtl.DTLVardef@1554d86org.highwire.dtl.DTLVardef@154a254org.highwire.dtl.DTLVardef@16d5c5b_HPS_FORMAT_FIGEXP M_FIG C_FIG

Electrostatic actuation is an emerging technology for generating tactile sensations on capacitive touchscreens through voltage-induced attractive forces between a fingertip and the surface. However, accurate control of electrostatic attraction during natural touchscreen interactions remains challenging because the applied normal force and sliding speed continuously vary, and their effects on the fingertip-screen contact and resulting actuation strength are not fully characterized. Here, we show how normal force and sliding speed systematically alter fingertip- screen contact area and electrical impedance, and use these measured changes to estimate electrostatic attraction during sliding. Contact area, interaction forces, and electrical impedance were measured simultaneously as participants slid their fingertips across an electrostatic surface under systematically varied normal forces and sliding speeds. These measurements revealed condition-dependent changes in fingertip contact, electrical interaction impedance, effective capacitance, derived effective gap thickness, and electrostatic attraction. We then incorporated these measured contact quantities into a physics-informed, data-driven model based on parallel-plate capacitor theory, in which effective capacitance, apparent contact area, and effective voltage determine the estimated electrostatic attraction. The resulting model links force- and speed-dependent changes in these quantities to electrostatic attraction while accounting for inter-participant variability through a participant-specific scaling factor. These findings provide experimentally grounded guidance for designing electrostatic surface-haptic feedback and future adaptive control strategies under realistic touch conditions.

A classical study found no excitation transfer when isolated cardiomyocytes were placed side by side, whereas a recent paper reported action potential transfer in carrdiomyocytes placed end to end. We use nanoscale numerical simulations based on the full Poisson-Nernst-Planck equations to investigate whether these apparently opposing observations can be explained by the different geometrical configurations. The computations show that in the end-to-end configuration, ephaptic coupling occurs when the intercellular cleft is sufficiently narrow and a sufficiently large fraction of the sodium channels is localized at the intercalated disc. Coupling is strengthened when the sodium channels are concentrated in fewer clusters and when ionic diffusion within the cleft is reduced. Under these conditions, excitation transfer occurs on a timescale consistent with rapid cell-to-cell activation. Conduction depends biphasically on cleft width and terminates abruptly beyond a critical width. Localization of potassium channels at the intercalated disc has only a moderate effect, whereas gap junctions substantially improve conduction and reduce the relative contribution of ephaptic coupling. In the side-by-side configuration, excitation transfer does not occur under physiological conditions and requires highly flattened cells, minimal separation, and unrealistically strong sodium-channel clustering. The different outcomes of the side-by-side and end-to-end experiments can therefore be explained by the fundamentally different geometrical conditions for ephaptic coupling.

Tau is a neuron-specific microtubule-associated protein that can self-associate into pathological insoluble aggregates or phase separate into condensates whose (patho)physiological role is debated. Recent studies suggest that intracellular surfaces can locally promote biomolecular condensation, even at low molecular concentrations. While microtubules in neurons provide an abundant tau-interaction surface, their role in tau phase separation remains unclear. Through a dialogue between experiments and theory, we demonstrate that tau forms multilayered condensates on microtubules at physiological concentrations via a prewetting-like transition. Concomitant tau-microtubule and tau-tau interactions explain the experimentally observed cooperative binding of the innermost tau layer directly adsorbed to the microtubule. The formation of this layer is dictated by the spacing of tubulin dimers within the microtubule lattice. Additional tau layers, driven by tau-tau interactions and independent of lattice spacing, are finite in thickness and unstable away from the microtubule surface. While the microtubule-adsorbed tau can selectively restrict proteins from the microtubule surface, the multilayered tau condensates can recruit tau interactors, such as RNA or soluble tubulin, highlighting the distinct roles of the condensate layers. Our results suggest that a prewetting-like transition constitutes a general physical mechanism for organizing liquid-like biomolecular layers of defined composition on charged intracellular surfaces.

Contact inhibition of proliferation (CIP) enables epithelial tissues to self-regulate growth and maintain tissue homeostasis. However, how cell-level mechanical contact, tissue-scale structural order, and proliferation kinetics interplay remains a fundamental open question in living matter physics. Here, we present a particle-based model of a confluent epithelial monolayer governed by overdamped dynamics, where individual cells interact via a two-dimensional hard core- soft shoulder potential. By comparing structural evolution during quasistatic densification with previously reported experimental division kinetics, we find that the dynamics of proliferation arrest mimics the onset of direct steric contacts between the hard cores of the shell. Identifying hard core contacts as the physical driver of CIP, we couple our mechanical model with a stochastic Monte Carlo division scheme in which the instantaneous division rate decreases to zero from an intrinsic value as the number of hard core contact increases to six from zero. We demonstrate that for high intrinsic division rates, the cellular densification outpaces mechanical relaxation. This kinetic mismatch drives premature hard-core contact formation, shifts the onset of jamming and contact inhibition to lower packing fractions, and induces increasingly disordered transient configurations before the tissue universally converges to a hexagonal close-packed limit. Our model's predicted division kinetics and structural order evolution are consistent with epithelial monolayer experiments, both reported and our own. This minimal physical framework links single-cell steric contact mechanics directly to tissue-scale growth regulation and structural evolution.

The mechanical properties of the nucleus are critical for maintaining nuclear integrity and function. We previously showed that chromatin dominates short-extension mechanics whereas lamins provide long-extension strain stiffening. To distinguish the roles of lamin isoforms, micromanipulation nucleus force measurements were performed on isolated nuclei from lamin A/C (Lmna-/-) and lamin B1 (Lmnb1-/-) knockout mouse embryonic fibroblast cells. Lamin A/C knockout does not alter short-extension nuclear stiffness but is essential for strain stiffening at longer extensions. Oppositely, lamin B1 loss reduced short-extension stiffness due to facultative heterochromatin loss while long-extension strain stiffening was slightly increased. Loss of lamin A/C and B1 resulted in similar lamin-chromatin linkers effects as LBR did not change and LAP2{beta} decreased in both. A simulation model of a polymeric lamin shell with stiff lamin A/C and softer lamin B1 subunits can qualitatively recapitulate experimental measurements of lamin knockout cells. Lamin A/C knockout resulted in abnormal nuclear shape but not nuclear blebbing or rupture whereas lamin B1 knockout, similar to other perturbations that cause heterochromatin loss, resulted in increased nuclear blebbing and rupture. This work illuminates the distinct mechanical roles of lamin A/C and B1 in determining nuclear structure and integrity.

Nanodiscs and bicelles are widely used as membrane mimetics for structural studies of membrane-associated systems. Studies have reported that their magnetic alignment behavior and phase stability are highly sensitive to composition and temperature. In this study, we systematically investigate the effects of cholesterol on bicelle formation and magnetic alignment in DMPC + 0.2 glycyrrhizic acid (GA) systems using a combined 31P and 14N solid-state NMR experimental and simulation-based approach. Temperature dependent 31P NMR spectra reveal a clear transition from vesicle dominant to aligned bicelles/nanodsics phase, while 1N quadrupolar splitting and lineshape analysis provides quantitative insights into heterogeneous lipid bilayer populations, distinguishing large aligned nanodiscs (B(L)), small nanodiscs (B(S)), and isotropic/random components (B(R)). A strong correlation is observed between the 31P derived bicelle fraction and the 14N B(L) population, confirming that macroscopic alignment in the presence of an external magnetic field directly reflects the growth of large, well-ordered nanodiscs. Cholesterol is found to play a critical dual role by modulating membrane order and curvature. At low cholesterol concentration (0 to 5 mole percent), nanodiscs alignment occurs gradually with increasing temperature, while at higher cholesterol concentration (15 to 25 mole percent), the alignment is delayed and accompanied by broader spectral features, indicating structural heterogeneity. Notably, 10 mole percent cholesterol consistently provides the optimal balance, enabling efficient temperature dependent conversion to aligned bicelles while maintaining high B(L) populations (about 70-80 percentage) and minimal isotropic fractions. In contrast, higher cholesterol maintains significant B(S) and B(R) populations, even at elevated temperature. The 14N quadrupolar coupling (Cq is approximately 8.5 to 9.2 kHz for aligned nanodiscs) remains nearly invariant across compositions, showing that cholesterol does not change local headgroup dynamics but instead redistributes lipid populations. These findings establish a combined 31P and 14N solid -state NMR approach provides a valuable platform for quantitatively correlating membrane structure, dynamics, and alignment, offering practical guidelines for optimizing bicelle systems for high resolution solid-state NMR studies of membrane associated biomolecules.

Hydrophobins are biosurfactant proteins that coat the cell surfaces of filamentous fungi. On the conidial surface, hydrophobins self-assemble into rodlets, forming a dense hydrophobic film that promotes air-dispersibility. Although rodlet formation is closely associated with the physiology of filamentous fungi, its underlying molecular mechanisms remain largely unknown. Previously, we revealed that RolA, a hydrophobin derived from Aspergillus oryzae, forms rodlets at the air-water interface. In this study, we focused on the flexible N-terminal region of RolA, which lacks a well-defined tertiary structure, and hypothesized that this intrinsically disordered region regulates rodlet formation. To investigate its role, we used RolA mutants with reduced charges in the N-terminal region and analyzed the rodlet formation process on the surface of a water-in-air sessile droplet using atomic force microscopy. In addition, we quantitatively characterized rodlet formation at the air-water interface by applying a kinetic perspective to the interfacial tension change profiles obtained from dynamic surface tension measurements. The results suggested that RolA first forms a monolayer at the air-water interface, then rodlet formation proceeds through the continuous supply of free RolA monomers from the bulk phase to the interfacial RolA film. Our molecular dynamics simulations of RolA at the interface supported a model in which RolA molecules within the interfacial film interact with free monomers in the bulk phase through their N-terminal regions. These results reveal a previously unidentified role of the N-terminal region in rodlet formation and provide a more comprehensive framework for understanding the molecular mechanism underlying RolA rodlet formation.

In the active loop extrusion model, the cohesin protein complex creates chromatin loops in eukaryotic cells. Extrusion maintains topologically associated domains (TADs), which are contiguous segments of chromatin that preferentially colocalize in space and are typically bounded by CTCF proteins that pause cohesin translocation. Here, we model active loop extrusion with hybrid molecular dynamics - Monte Carlo simulations in entangled flexible linear polymer melts. Intra-chain contact probabilities of polymers with active loop extrusion are enhanced compared to their equilibrium, passive counterparts. Extrusion causes the size of chain segments to be much smaller than in passive melts. While the overlap parameter in passive melts without extrusion monotonically increases with segment length, it is nonmonotonic in active melts and on the order of unity within the parameters of this study. Active loop extrusion suppresses contacts between TADs in favor of intra-TAD contacts. Reduction of overlaps between chain segments dilutes entanglements in active melts. Depending on parameters, active extrusion without TADs may induce more compact conformations than with TADs, due in part to fractal loopy globule-like dynamics. This work suggests that active loop extrusion reduces overlaps between TADs, contributing to effective gene regulation by cis-regulatory elements.

BackgroundPlatelet activation in flowing blood is a multiscale process in which vessel-scale hemodynamics, red blood cell (RBC) mechanics, adhesive receptor interactions, and intracellular signalling jointly determine thrombotic risk. Individual components are well studied, but a single reduced description that carries each explicitly from vessel-scale flow to mechanosensitive calcium entry, with dimensionally consistent couplings, remains uncommon. ObjectivesWe develop and analyse a reduced, six-module mechanobiological framework for platelet priming spanning the cascade from hemodynamic shear to mechanosensitive calcium entry, and we delineate which elements are supported by existing evidence and which are new, testable hypotheses. MethodsThe framework comprises six coupled modules: (I) hemodynamic forcing from the incompressible Navier-Stokes equations, with an objective principal-strain-rate measure for extensional flow; (II) RBC-mediated platelet margination and near-wall delivery, closed by a near-wall arrival flux; (III) von Willebrand factor (VWF) activation with a bounded kernel and glycoprotein Ib (GPIb) catch-slip capture, resolved through an explicit contact area and a bond-dependent mobility that progressively immobilises wall-interacting platelets; (IV) a single-load membrane-stimulus formulation; (V) mechanosensitive gating and a dimensionally consistent cytosol-store calcium model with extracellular influx; and (VI) a phenomenological mechanical-memory state. We formally derive that the single-platelet stochastic dynamics and the continuum population balance form a Fokker-Planck pair, with the spatially varying diffusivity handled by an explicit drift correction. ResultsThe framework yields a family of mechanochemical dimensionless groups delineating priming regimes. Its central prediction is reformulated as a falsifiable, history-sensitive signature: in a conditioning-test protocol, a low-tension conditioning block charges the memory state, and a fixed sub-threshold test pulse then reports a delay-dependent calcium facilitation that decays on the memory time{tau} m and is distinguishable from no-memory gating, channel adaptation, and residual-calcium priming. We show explicitly that the previously proposed pulsatile-versus-monotone contrast is a nonlinear convexity/thresholding effect of the gating nonlinearity--its difference-in-differences is approximately zero-- and is therefore not a valid test of memory; the conditioning-test signature is. A second prediction links RBC stiffening to reduced near-wall delivery and captured-platelet calcium response, upstream of intrinsic platelet signalling. ConclusionsThe framework provides a dimensionally consistent, mechanistically grounded and hypothesis-generating description linking hemodynamic forcing to mechanosensitive calcium entry. It demonstrates how history-dependent platelet priming may arise from a phenomenological sensitisation state and proposes a conditioning-test protocol for comparison against adhesive, channel and intracellular-store persistence. The framework is calibratable rather than validated, and the quantitative outputs shown use representative uncalibrated parameters.