Self-assembly of dry amphiphilic lipid films on surfaces upon hydration is a crucial step in the formation of cell-like giant unilamellar vesicles (GUVs). GUVs are useful as biophysical models, as soft materials, as chassis for bottom-up synthetic biology, and in biomedical applications. Here combined quantitative measurements of the molar yield and distributions of sizes and high-resolution imaging of the evolution of thin lipid films on surfaces, we report the discovery of a previously unknown pathway of lipid self-assembly which can lead to ultrahigh yields of GUVs of >50%. This yield is about 60% higher than any GUV yield reported to date. The "shear-induced fragmentation" pathway occurs in membranes containing 3 mol% of the poly(ethylene glycol) modified lipid PEG2000-DSPE (1,2-distearoyl--glycero-3-phosphoethanolamine--[methoxy(polyethylene glycol)-2000]), when a lipid-dense foam-like mesophase forms upon hydration. The membranes in the mesophase fragment and close to form GUVs upon application of fluid shear. Experiments with varying mol% of PEG2000-DSPE and with lipids with partial molecular similarity to PEG2000-DSPE show that ultrahigh yields are only achievable under conditions where the lipid-dense mesophase forms. The increased yield of GUVs compared to mixtures without PEG2000-DSPE was general to flat supporting surfaces such as stainless steel sheets and to various lipid mixtures. In addition to increasing their accessibility as soft materials, these results demonstrate a route to obtaining ultrahigh yields of cell-sized liposomes using longstanding clinically-approved lipid formulations that could be useful for biomedical applications.

The challenges for clinical application of small-diameter vascular graft are mainly acute/chronic thrombosis, inadequate endothelialization, intimal hyperplasia caused by inflammation, oxidative stress, and the mismatch of mechanical compliance after transplantation. How to construct an effective regenerative microenvironment through a material with uniform dispersion of active components is the premise of maintaining patency of a vascular graft. In this study, we have compounded poly(ester-urethane)urea (PEUU) with various optimized concentrations of resveratrol (Res) by homogeneous emulsion blending, followed by electrospinning into the hybrid PEUU/Res nanofibers (P/R-0, P/R-0.5, P/R-1.0, and P/R-1.5). Then the microstructure, surface wettability, mechanical properties, degradation, Res sustained release properties, hemocompatibility, and cytocompatibility of P/R were evaluated comprehensively. The results indicate that Res can be gradually released from the P/R, and both the hydrophilicity and antioxidant ability of the nanofiber gradually increase with the increase of Res content. Moreover, with the increase of Res, the viability and proliferation behavior of HUVECs were significantly improved. Meanwhile, tube formation and migration experiments showed that Res promoted the formation of a neovascularization network. In brief, it is concluded that P/R-1.0 is the optimal candidate with a uniform microstructure, moderate wettability, optimized mechanical properties, reliable hemocompatibility and cytocompatibility, and strongest ability to promote endothelial growth for the vascularizing matrix.

Understanding the interactions of guest molecules like proteins and nanoparticles with microgels is fundamental for using microgels as nanocarriers. However, understanding and predicting the system properties becomes increasingly difficult as the systems become more complex. In this study, we systematically investigated the uptake of these guest molecules in a pH-responsive polyelectrolyte microgel modeled as a bead-spring network using Monte Carlo simulations. To narrow down the complexity of the systems, we modeled the guest molecules as simple charged beads. The simulations included the variation of (i) guest molecule charge, (ii) size, and (iii) number, as well as the influence of (iv) the addition of salt. The effect of these parameters on the ionization, swelling, and guest molecule uptake was investigated. The uptake of guest molecules with higher charges enhanced the ionization of the microgel at low pH. The strongest effect was observed for beads with charge = +15. For higher guest molecule charges, the polymer chains could not fully wrap around the guest molecules, to provide enough microgel charges to fully compensate for the repulsive interactions between the guest beads. In general, the uptake of guest molecules leads to a collapse of the microgel due to attractive electrostatic interactions. With the increasing size of the guest molecules, their excluded volume increases, and the microgel swells with their uptake. Adding monovalent salt slightly decreases the uptake at low ionization of the network due to electrostatic screening. The presence of salt ions with higher valency further decreases the uptake of guest molecules into a fully ionized microgel.

Polyelectrolyte hydrogels can deform under electric fields due to their unique nature combining polymer elasticity and electrostatics within a single structure. While the response of hydrogels to electric fields is relatively well-characterized at the macroscale, at the mesoscale-where the behaviour of the constituent chains becomes significant-the effect of external electric potentials on the hydrogel structure is poorly understood. In this study, we explored the mechanical response of a semi-infinite polyelectrolyte hydrogel slab to transient, sinusoidal electric fields using extensive coarse-grained molecular dynamics simulations with both short and long-range electrostatics. Our simulations show that when the electric field is applied to a small volumetric section of the hydrogel slab spatially nonuniformly, the entire slab contracts reversibly and in a direction perpendicular to the field. The hydrogel contracts to almost half of its initial, field-free length before retracting to its original size, with its size fluctuations eventually decaying similar to an underdamped oscillator. Contraction is maximized if the electric field is applied to the central region of the slab, away from the slab's interfaces. Additionally, tuning the electric field frequency and amplitude controls both contraction times and contraction efficiency. Further analyses using implicit solvent simulations across various electrostatic parameters and salt concentrations confirm the robustness of the phenomenon while highlighting the importance of hydrodynamics. Our results demonstrate the effectiveness of electric fields applied spatially nonuniformly on homogeneous hydrogel structures, with potential applications in electro-mechanochemistry.

Active particles are self-propelling in nature due to the generation of a fore-aft asymmetry in the concentration of solutes around their surface. Both the surface activity and mobility play an important role in the particle dynamics. The solutes are the products of the chemical reaction between the active particle surface and suspending medium. Unlike Janus particles, isotropic active particles have been shown to undergo spontaneous self-propulsion beyond a critical particle size (or the Péclet number). Compared to Janus active particles, there is a third ingredient, namely, advection-induced instability that dictates the dynamics of such particles. The present study numerically investigates the role played by shear rate-dependent viscosity of a suspending medium in the self-phoretic dynamics of such isotropic active particles. Towards this, a non-Newtonian Carreau fluid is taken as the suspending medium. One of the important findings of this study is the presence of a second critical Péclet number beyond which the spontaneous motion of the particle ceases to exist. Even though this critical Péclet number had been previously investigated for Newtonian fluids, strong dependence of the former on the rheology of the suspending medium was not explored. The analysis also shows that a shear thinning fluid significantly reduces the maximum velocity of the particle. In addition, confinement is found to have a significant effect on the axial propulsive velocity of the particle suspended in a Carreau fluid.

We investigate the link between the internal microstructure of poly(-isopropylacrylamide)-poly(ethylene glycol) methyl ether methacrylate (PNIPAM-PEGMA) microgels, their bulk moduli and the rheological response and structural arrangement in dense suspensions. The low degree of crosslinking combined with the increased hydrophilicity induced by the presence of PEGMA results in a diffuse, star-like density profile of the particle and very low values of the bulk modulus in dilute conditions, as determined by small angle neutron scattering (SANS). The ultrasoft nature of the particle is reflected in the changes of the structural arrangement in dense suspensions, which evidence a strong deswelling and a sharp rise of the bulk modulus at moderate packing fractions. At larger packings the single particle morphology and softness saturate, and we observe a structural transition from a dispersion-like to a hydrogel-like behavior. The transition is also reflected in the rheological response in the form of a two-step yielding at large packing fractions, characteristic of systems in which a network structure is present. Our results demonstrate that a knowledge of the internal structure and mechanics of individual microgels is needed to determine and tune the properties of dense suspensions, and optimize their response for applications in biomedicine and as filtration systems.

Peptide-polymer systems hold strong potential for applications in nanotherapeutics. Desmopressin, a synthetic analogue of the antidiuretic hormone arginine vasopressin, may serve as a valuable case of study in this context since it is a first-line treatment for disorders affecting water homeostasis, including diabetes insipidus. It also has an established use as a hemostatic agent in von Willebrand disease, and recently, its repurposing has been suggested as a neoadjuvant in the treatment of certain types of cancer. Despite its well-documented clinical uses, studies on the supramolecular organization of desmopressin and its association with polymers remain scarce, limiting the therapeutic benefits of these nanostructured arrays. Here, we investigate the self-assembly of desmopressin and its association with sodium polystyrene sulphonate (NaPSS), a potassium-binding polymer used to treat hyperkalemia. Using structural techniques such as small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and atomic force microscopy combined with infrared nanospectroscopy (AFM-IR), we identified that desmopressin associates with NaPSS to form hybrid fibrillar nanoassemblies characterized by β-turn enriched domains and the appearance of β-sheet content. cytotoxicity assays conducted on breast cancer cell lines MCF-7 and MDA-MB-231 showed that NaPSS/desmopressin complexes are well-tolerated by the non-metastatic MCF-7 cells while displaying inhibitory effects against the metastatic MDA-MB-231 cells. The findings presented here, which demonstrate the successful association between two clinically validated drugs and the ability of the hybrid matrix to modulate cell interactions, potentially contribute to the design of peptide-polymer therapeutic systems.

In this work, with the intent of exploring the out-of-equilibrium polymerization of active patchy particles in linear chains, we study a suspension of active bifunctional Brownian particles (ABBPs). At all studied temperatures and densities, ABBPs self-assemble in aggregating chains, as opposed to the uniformly space-distributed chains observed in the corresponding passive systems. The main effect of activity, other than inducing chain aggregation, is to reduce the chain length and favour the alignment of the propulsion vectors in the bonding process. At low activities, attraction dominates over activity in the bonding process, causing self-assembly to occur randomly regardless of the particle orientations. Interestingly, we find that at the lowest temperature, as density increases, chains aggregate forming a novel state: MISP, , motility-induced spirals, where spirals are characterised by a finite angular velocity. In contrast, at the highest temperature, density and activity, chains aggregate forming a different novel state (a spinning crystalline cluster) characterised by a compact and hexagonally ordered structure, both translating and rotating. The rotation arises from an effective torque generated by the presence of competing domains where particles self-propel in the same direction.

A composite of a knitted fabric and a soft matrix enables applications that require low stiffness and high crack resistance. Examples include heart valves and stretchable strain sensors. Here we study processes of crack growth in such a composite under monotonic and cyclic stretch. We fabricate a composite using a knitted fabric of nylon yarn and an elastomer matrix of polycarbonate urethane. We precut a sample with a crack, monotonically stretch the sample, and observe the growth of the crack. The crack grows in the matrix as the yarn slips and breaks. The stretch is converted to energy release rate . We identify two critical energy release rates, and . When < , the yarn does not slip, and the crack does not grow in the matrix. When < < , the yarn slips but does not break, and the crack grows in the matrix stably and arrests when the stretch stops increasing. When = , the yarn slips and breaks, while the crack grows unstably. When the sample is subject to cyclic stretch, we observe analogous behavior of crack growth and arrest, as well as yarn slip and yarn break. However, the two critical values, and , are much smaller than the corresponding values under monotonic stretch.

We present an experimental study on the evaporation of drops on fibers. More specifically, we focus on the droplet lifetime both in quiescent air and in an air flow of constant velocity. We propose a model to describe the evaporation rate and lifetime in a purely diffusive regime, which includes the liquid cooling associated with evaporation and the thermal conductivity of the atmosphere and the fiber. Our model effectively captures the primary physical behaviors, demonstrating a semi-quantitative agreement with our measurements across various liquids and fiber materials. Finally, the model is generalized to a convective air flow, which also rationalizes our experimental data.

It is long known that particles of the same material but with different sizes charge with different polarities in mutual collisions. In most cases, the smaller grains become negative. Here, we study tribocharging of (sub-)mm dust aggregates in the course of microgravity experiments by determining the charges of particles through their motion within an electric field. Similar experiments were already conducted with monolithic grains. Here, the constituent dust grains in an aggregate add complexity to the process of tribocharging in various ways. This ranges from the dust size scale, setting local surface curvatures, over shifting grains during collisions, altering the outer surfaces and potentially generating sub-surface tribocharging, to material-dependent tribocharging with a non-homogeneous dust composition. Nevertheless, in concert with the usual size dependence, the small aggregates predominantly charge negatively, the large population charges predominantly positively.

Localized stress concentrations at fiber ends in short fiber-reinforced polymer composites (SFRCs) significantly affect their mechanical properties. Our research targets these stress concentrations by embedding nitro-spiropyran (SPN) mechanophores into the polymer matrix. SPN mechanophores change color under mechanical stress, allowing us to visualize and quantify stress distributions at the fiber ends. We utilize glass fibers as the reinforcing material and employ confocal fluorescence microscopy to detect color changes in the SPN mechanophores, providing real-time insights into the stress distribution. By combining this mechanophore-based stress sensing with finite element analysis (FEA), we evaluate localized stresses that develop during a single fiber pull-out test near different fiber end geometries-flat, cone, round, and sharp. This method precisely quantifies stress distributions for each fiber end geometry. The mechanophore activation intensity varies with fiber end geometry and pull-out displacement. Our results indicate that round fiber ends exhibit more gradual stress transfer into the matrix, promoting effective stress distribution. Also, different fiber end geometries lead to distinct failure mechanisms. These findings demonstrate that fiber end geometry plays a crucial role in stress distribution management, critical for optimizing composite design and enhancing the reliability of SFRCs in practical applications. By integrating mechanophores for real-time stress visualization, we can accurately map quantified stress distributions that arise during loading and identify failure mechanisms in polymer composites, offering a comprehensive approach to enhancing their durability and performance.

Proteinase K, a serine protease from , is crucial in research due to its potent proteolytic activity, which relies on conformational stability and substrate affinity. Glutathione (GSH), an essential intracellular antioxidant, regulates various physiological processes by interacting with proteins, influencing their stability and function. Despite the importance of both proteinase K and GSH, their potential interaction remains unexplored. Understanding this interaction could uncover new regulatory mechanisms affecting proteinase K, with significant implications for research and therapeutic applications. In this study, we systematically investigated the binding of GSH to proteinase K using a comprehensive approach in which theoretical and experimental methods mutually validate each other. Molecular docking determined the binding mode and the interaction mechanism of proteinase K and GSH. Molecular dynamics (MD) simulations revealed that GSH binding significantly improved the stability of proteinase K, affirming the binding process was spontaneous, with hydrogen bonds and van der Waals forces emerging as the predominant contributors throughout the interaction. At the same time, the fluorescence spectrum and circular dichroism spectrum confirmed the interaction mechanism between GSH and proteinase K, as well as the conformational changes of proteinase K induced by GSH binding. We believe this study could offer valuable insights for future research into the structure and binding dynamics of other protein-ligand complexes under physiological conditions.

Material extrusion-based three-dimensional (3D) printing is a widely used manufacturing technology for fabricating scaffolds and devices in bone tissue engineering (BTE). This technique involves two fundamentally different extrusion approaches: solution-based and melt-based printing. In solution-based printing, a polymer solution is extruded and solidifies solvent evaporation, whereas in melt-based printing, the polymer is melted at elevated temperatures and solidifies as it cools post-extrusion. Solution-based printing can also be enhanced to generate micro/nano-scale porosity through phase separation by printing the solution into a nonsolvent bath. The choice of the printing method directly affects scaffold properties and the biological response of stem cells. In this study, we selected polycaprolactone (PCL), a biodegradable polymer frequently used in BTE, blended with hydroxyapatite (HA) nanoparticles, a bioceramic known for promoting bone formation, to investigate the effects of the printing approach on scaffold properties and performance using human mesenchymal stem cells (hMSCs). Our results showed that while both printing methods produced scaffolds with similar strut and overall scaffold dimensions, solvent-based printing resulted in porous struts, higher surface roughness, lower stiffness, and increased crystallinity compared to melt-based printing. Although stem cell viability and proliferation were not significantly influenced by the printing approach, melt-printed scaffolds promoted a more spread morphology and exhibited pronounced vinculin staining. Furthermore, composite scaffolds outperformed their neat counterparts, with melt-printed composite scaffolds significantly enhancing bone formation. This study highlights the critical role of the printing process in determining scaffold properties and performance, providing valuable insights for optimizing scaffold design in BTE.

The relationship between the dynamics and structure of amorphous thin films and nanocomposites near their glass transition is an important problem in soft-matter physics. Here, we develop a simple theoretical approach to describe the density profile and the α-relaxation time of a glycerol-silica nanocomposite (S. Cheng , , 2015, , 194704). We begin by applying the Derjaguin approximation, where we replace the curved surface of the particle with the planar one; thus, modeling the nanocomposite is reduced to that of a confined thin film. Subsequently, by employing the molecular dynamics (MD) simulation data of Cheng , we approximate the density profile of a supported liquid thin film as a stationary solution of a fourth-order partial differential equation (PDE). We then construct an appropriate density functional, from which the density profile emerges through the minimization of free energy. Our final assumption is that of a consistent, temperature-independent scaled density profile, ensuring that the free volume throughout the entire nanocomposite increases with temperature in a smooth, monotonic fashion. Considering the established relationship between glycerol relaxation time and temperature, we can employ Doolittle-type analysis ("naïve" free-volume model), to calculate the relaxation time based on temperature and film thickness. We then convert the film thickness into the interparticle distance and subsequently the filler volume fraction for the nanocomposites and compare our model predictions with experimental data, resulting in a good agreement. The proposed approach can be easily extended to other nanocomposite and film systems.

The layered structure of smectic liquid crystals cannot develop unobstructed when confined to spherical shells with layers extending in the radial direction, since the available cross section area increases from the inside to the outside of the shell yet the number and thickness of layers must be constant. For smectic-A (SmA) liquid crystals, with the layer normal parallel to the director , the frustration breaks up the texture into spherical lune domains with twist deformations of alternating sense, overlaid with a herringbone-like secondary modulation and mediated localized bend regions where the boundary conditions are violated. The SmC phase has more degrees of freedom to resolve the frustration thanks to its non-zero tilt angle between and , but its response to tangential shell confinement was never studied. We show experimentally and theoretically that the lunes in shells undergoing a SmA-SmC transition become twice as wide and half as many and they lose the secondary modulation, adopting a configuration with no layer twist but uniform layer bend if reaches a large enough value. Our study expands our understanding of how smectics respond to spherical confinement and it opens new soft matter research opportunities, given the rich diversity of phases with SmC-like symmetry, including chiral and spontaneously polarized phases.

In the present work we have studied collectives of active disks with an energy depot, moving in the two-dimensional plane and interacting an excluded volume. The energy depot accounts for the extraction of energy taking place at the level of each particle in order to perform self-propulsion, included in an underdamped Langevin dynamics. We show that this model undergoes a flocking transition, exhibiting some of the key features of the Vicsek model, namely, band formation and giant number fluctuations. These bands, either single or multiple, are dense and very strongly polarised propagating structures. Large density bands disappear as the activity is further increased, eventually reaching a homogeneous polar state. We unravel an effective alignment interaction at the level of two-particle collisions that can be controlled by activity and gives rise to flocking at large scales.

A photoresponsive variant of the paradigmatic active nematic fluid made of microtubules and powered by kinesin motors is studied in a conventional two-dimensional interface under blue-light illumination. This advantageously permits the system's performance to be assessed under conditions of spatially distributed activity. Both turbulent and flow aligning conditions are separately analyzed. Under uniform illuminating conditions, active flows get enhanced, in accordance with previous observations. In contrast, patterning the activity appears to disturb the effective activity measured in terms of the vorticity of the elicited flows. We interpret this result as alternative evidence of the important role played by the active length scale in setting not only the textural and flow characteristics of the active nematic but also, most importantly, the range of material integrity. Our research continues to explore perspectives that should pave the way for an effective control of such an admirable material.

Viscous fingering (VF) and elastic fracture (EFr) are prevalent phenomena when gas invades into complex fluids. In this study, compressed nitrogen gas was injected into a complex fluid called magnesium lithium phyllosilicate (MLPS) suspension through a single-point injection in a rectangular Hele-Shaw cell. In the case of gas invasion into the MLPS suspension VF, the affected area is confined to the tips of the independently growing fingers after splitting. Within the affected region, the velocity is primarily parallel to the growth direction of fingers, while the perpendicular component is mainly distributed on the outer sides of the whole bubble and within a more limited range. The gas-liquid interface can be divided into moving and static boundaries, where the length of the moving boundary is much smaller than the perimeter of the bubble. On the moving boundary, the parallel velocity component to the growth direction is significantly greater than the perpendicular component in terms of both the influence range and magnitude. The included angles between the velocity direction and the growth direction are concentrated within a narrow range, showing a significant positive correlation among the velocities. Conversely, when a bubble invades EFr, the disturbed area is larger, with the parallel velocity component primarily located at the tip and the perpendicular component distributed in a "butterfly" shape around the middle of the bubble. The moving boundary length is comparable to the bubble perimeter. On the moving boundary, the perpendicular component exerts a non-negligible influence, and the distribution of included angles is more uniform, resulting in a significant negative correlation among the velocities. Based on the above characteristics of the velocity field, quantitative indicators, such as the ratio of the affected area, the ratio of moving boundary length to the perimeter, the velocity component ratio, the coefficient of uniformity, and the relative correlation length, are proposed. Based on the velocity field, these indicators demonstrate universal applicability in distinguishing between the two different invasion patterns observed in complex fluids.

Surfactant-laden fluid interfaces of soft colloids, such as bubbles and droplets, are ubiquitously seen in various natural phenomena and industrial settings. In canonical systems where microparticles are driven in hydrodynamic flows, convection of the surfactant changes local surface tension. Subsequently, the interplay of Marangoni and hydrodynamic stresses leads to rich interfacial dynamics that directly impact the particle motions. Here we introduce a new mechanism for self-propelled droplets, driven by a thin layer of chemically active microparticles situated at the interface of a suspended droplet, which is a direct extension of the planar collective surfing model by Masoud and Shelley (H. Masoud and M. J. Shelley, , 2014, , 128304). These particles can generate chemicals locally, leading to spontaneous Marangoni flows that drive the self-aggregation of microparticles. This process, in turn, creates a polarized surfactant distribution, which induces collective chemotaxis and dipolar bulk flows, ultimately breaking the symmetry. By assuming the local surfactant production to be either proportional to particle density or saturated at a high particle density, we observe that the system can be chemotactically diverging or approach a steady state with constant migration velocity. The system is studied analytically in the linear region for the initial transient dynamics, yielding critical numbers and familiar patterns, as well as numerically for larger amplitudes and over a long time using spectral methods.

The assembly and dynamics of polyelectrolyte complexes (PECs) and polyelectrolyte multilayers (PEMs) are influenced by water content, pH, and salt concentration. However, the influence of divalent salts on the assembly of polyelectrolyte complexes remains unclear. This work showcases that divalent chloride salts directly impact the glass transition temperature and the ion-ion interactions within PECs. Here, poly(diallyldimethylammonium)-poly(styrene sulfonate) (PDADMA-PSS) PECs are assembled in solutions containing MgCl and CaCl (following the Hofmeister series). These PECs are studied for the cations' influence on physicochemical properties (glass transition, polymer composition, ion pairing) at varying salt concentrations (0.03 M, 0.10 M, 0.15 M, and 0.20 M). Modulated differential scanning calorimetry (MDSC) experiments demonstrate that PECs assembled with CaCl have a significantly higher glass transition temperature when compared to PECs assembled with MgCl. Neutron activation analysis (NAA) and nuclear magnetic resonance (NMR) spectroscopy demonstrate that this difference is due to strong ion-specific effects influencing the ratio of intrinsic and extrinsic ion pairings in the system. Furthermore, this study demonstrates a universal linear relationship between the thermal transition and the number of water molecules surrounding oppositely charged polyelectrolyte-polyelectrolyte intrinsic ion pairs, even when the salt contains divalent cations. Ion-specific trends have implications on the glass transition and composition of PDADMA-PSS PECs. Divalent salts not only follow the trend of the Hofmeister series but also introduce bridging into the polyelectrolyte complex; however, the structural relaxation of the PEC remains the same. This study offers a bridge between divalent cation behavior on polymer assembly properties and its transition to industrial applications such as controlled drug delivery, sensors, and water purification.