Interfacial exchange dynamics of biomolecular condensates are highly sensitive to client interactions.

Phase separation of biomolecules can facilitate their spatiotemporally regulated self-assembly within living cells. Due to the selective yet dynamic exchange of biomolecules across condensate interfaces, condensates can function as reactive hubs by concentrating enzymatic components for faster kinetics. The principles governing this dynamic exchange between condensate phases, however, are poorly understood. In this work, we systematically investigate the influence of client-sticker interactions on the exchange dynamics of protein molecules across condensate interfaces. We show that increasing affinity between a model protein scaffold and its client molecules causes the exchange of protein chains between the dilute and dense phases to slow down and that beyond a threshold interaction strength, this slowdown in exchange becomes substantial. Investigating the impact of interaction symmetry, we found that chain exchange dynamics are also considerably slower when client molecules interact equally with different sticky residues in the protein. The slowdown of exchange is due to a sequestration effect, by which there are fewer unbound stickers available at the interface to which dilute phase chains may attach. These findings highlight the fundamental connection between client-scaffold interaction networks and condensate exchange dynamics.

Ionic Distribution of an Unequal Electrolyte Near an Air/Water Surface.

The distribution of electrolytes near the air/water surface plays an essential role in many processes. While the general distribution is governed by classic Poisson-Boltzmann statistics, the analytical solution is only available for symmetric electrolytes. From the recent studies in the literature, it is evident that surface adsorption is dependent on specific ions as well as the H-bond structure at the surface. Experimental data can capture the macro properties of the surface, such as surface tension and surface potential. Yet, the underpinning mechanisms behind this experimental macro-observation remain unclear. To address the challenge, we developed a framework combining experimental studies and numerical calculations. The model was developed for electrolytes with unequal cationic and anionic charges. The asymmetric model was successfully applied to describe the surface charge of MgCl 2 aqueous solution. The results can be explained by the role of cationic size and charge on the surface layer.

Oil and Organic Liquids Incorporation into Fresh Geopolymer Pastes Using Suitable Quaternary Ammonium Surfactants.

The direct incorporation of low viscosity organic liquids (OL) such as dodecane and tributylphosphate (TBP) into fresh geopolymers (GP) is difficult and generally leads to variable amounts of un-incorporated OL remaining outside the hardened geopolymer. Experimentally, it is observed that a regular torque increase during OL incorporation corresponds to a suitable dispersion of the OL in the form of fine micrometric droplets. This can be obtained for TBP and dodecane by adding a small quantity of quaternary ammoniums salts (QAs) such as cetyltrimethylammonium bromide (CTAB). Shorter alkyl chains QAs, such as hexamethyltrimethylammonium (HMTA) can also be used but with a reduced efficiency. The positive impact of CTAB is then confirmed by the Washburn capillary rise method, showing that the interactions between TBP and CTAB-modified metakaolin are weaker compared to untreated powder. Finally, it is observed that the incorporation of TBP into geopolymer slurries is much easier than the incorporation of dodecane. The low interfacial tension measured between TBP and the activating solution (around 8 mN·m -1 ), contrasting with dodecane (29 mN·m -1 ), explains that the dispersion of TBP droplets in fresh metakaolin suspensions is more efficient.

Exploration of surface tension measurement methods for pharmaceutical excipients.

Surface tension is a crucial functional indicator for various classes of pharmaceutical excipients, as highlighted in both the Pharmacopoeia of the People's Republic of China (ChP) < 9601 Guidelines for Functionality-related Characteristics of Pharmaceutical Excipients > and the United States Pharmacopoeia (USP) < 1059 Excipient Performance >. However, there are few systematic studies on surface tension measurement of pharmaceutical excipients, resulting in a lack of stable parameter support in practical applications. In this study, we aim to fill this gap by exploring three different methods for measuring surface tension. These methods were carefully developed taking into account the actual measurement process and statistical theory, thus ensuring their applicability and reliability. Through comparative analyses, we have identified the most suitable measurement methods for different classes of pharmaceutical excipients. In addition, this paper describes the surface adsorption behavior of various excipients. Therefore, this study provides valuable guidance for the determination of surface tension and the study of surface adsorption behavior, which lays the foundation for further comprehensive research in the field of surface tension of pharmaceutical excipients and the improvement of general pharmacopoeia specification.

Destabilization of a model O/W/O double emulsion: From bulk to interface.

Oil-in-water-in-oil (O/W/O) double emulsions are considered an advanced oil-structuring technology that can accomplish multi-functions to improve food quality and nutrition. However, this special structure is thermodynamically unstable. This study formulated a model O/W/O double emulsion with standard surfactants, Tween 80 (4 %) and polyglycerol polyricinoleate (PGPR, 5 %), using a traditional two-step method with different homogenization parameters. Cryo-SEM and GC-FID results show that O/W/O emulsions were successfully formulated, and the release rate (RR) of medium-chain triglycerides (MCT) oil from the inner oil to the outer oil phase increased significantly with 2nd homogenization speed increasing, respectively. Interestingly, the RR of all samples reached about 75 % after 2 months of storage, suggesting that O/W/O emulsions were highly unstable. To explain the observed instability, dynamic interfacial tension and interfacial rheology were performed using a drop shape tensiometer. Results demonstrated that unadsorbed Tween 80 in the intermediate aqueous phase was a key factor in markedly decreasing the interfacial properties of the outer PGPR-assembled film by affecting the interfacial rearrangement. Additionally, it was found that the MCT release showed a positive correlation with the Tween 80 concentration, demonstrating that the formed Tween 80 micelles could transport oil molecules to strengthen the emulsion instability. Taken together, this study reveals the destabilization mechanism of model O/W/O surfactants-stabilized emulsions from bulk to interface, providing highly relevant insights for the design of stable O/W/O double emulsions.

Integration of IFAST-based nucleic acid extraction and LAMP for on-chip rapid detection of Agroathelia rolfsii in soil.

Agroathelia rolfsii (A. rolfsii) is a fungal infection and poses a significant threat to over 500 plant species worldwide. It can reduce crop yields drastically resulting in substantial economic losses. While conventional detection methods like PCR offer high sensitivity and specificity, they require specialized and expensive equipment, limiting their applicability in resource-limited settings and in the field. Herein, we present an integrated workflow with nucleic acid extraction and isothermal amplification in a lab-on-a-chip cartridge based on immiscible filtration assisted by surface tension (IFAST) to detect A. rolfsii fungi in soil for point-of-need application. Our approach enabled both DNA extraction of A. rolfsii from soil and subsequent colorimetric loop-mediated isothermal amplification (LAMP) to be completed on a single chip, termed IFAST-LAMP. LAMP primers targeting ITS region of A. rolfsii were newly designed and tested. Two DNA extraction methods based on silica paramagnetic particles (PMPs) and three LAMP assays were compared. The best-performing assay was selected for on-chip extraction and detection of A. rolfsii from soil samples inoculated with concentrations of 3.75, 0.375 and 0.0375 mg fresh weight per 100-g soil (%FW). The full on-chip workflow was achieved within a 1-h turnaround time. The platform was capable of detecting as low as 3.75 %FW at 2 days after inoculation and down to 0.0375 %FW at 3 days after inoculation. The IFAST-LAMP could be suitable for field-applicability for A. rolfsii detection in low-resource settings.

Interfacial assembly and rheology of multi-responsive glycyrrhizic acid at liquid interfaces.

Glycyrrhizic acid (GA), a naturally derived food-grade saponin molecule, is a promising alternative to synthetic surfactants for stabilizing multiphase systems including emulsions and foams, due to its biological activity and surface-active properties. Understanding the interfacial behavior of GA, particularly in relation to its complex self-assembly behaviors in water induced by multiple environmental stimuli, is crucial to its application in multiphase systems. In this study, we comprehensively investigate the interfacial structure and rheological properties of GA systems, as a function of pH and temperature, through Langmuir-Blodgett films combined with atomic force microscopy, interfacial particle tracking, adsorption kinetics, stress-relaxation behavior and interfacial dilatational rheology. The variation of solution pH provokes pronounced changes in the interfacial properties of GA. At pH 2 and 4, GA fibril aggregates/fibrils adsorb rapidly, followed by rearrangement into large lamellar and rod-like structures, forming a loose and heterogeneous fibrous network at the interface, which exhibit a stretchable gel-like behavior. In contrast, GA at pH 6 and 8, featuring micelles or monomers in solutions, adsorb slowly to the interface and re-assemble partially into small micelle-like or irregular structures, which lead to a dense and homogeneous interfacial layer with stiffer glassy-like responses. With successively elevated temperature, the GA structures (pH 4) at the interface break into smaller fragments and further adsorption is promoted. Upon cooling, the interfacial tension of GA further decreases and a highly elastic interfacial layer may be formed. The diverse GA assemblies in bulk solution impart them with rich and intriguing interfacial behaviors, which may provide valuable mechanistic insights for the development of novel edible soft matter stabilized by GA.

New Trends in Biosurfactants: From Renewable Origin to Green Enhanced Oil Recovery Applications.

Enhanced oil recovery (EOR) processes are technologies used in the oil and gas industry to maximize the extraction of residual oil from reservoirs after primary and secondary recovery methods have been carried out. The injection into the reservoir of surface-active substances capable of reducing the surface tension between oil and the rock surface should favor its extraction with significant economic repercussions. However, the most commonly used surfactants in EOR are derived from petroleum, and their use can have negative environmental impacts, such as toxicity and persistence in the environment. Biosurfactants on the other hand, are derived from renewable resources and are biodegradable, making them potentially more sustainable and environmentally friendly. The present review intends to offer an updated overview of the most significant results available in scientific literature on the potential application of biosurfactants in the context of EOR processes. Aspects such as production strategies, techniques for characterizing the mechanisms of action and the pros and cons of the application of biosurfactants as a principal method for EOR will be illustrated and discussed in detail. Optimized concepts such as the HLD in biosurfactant choice and design for EOR are also discussed. The scientific findings that are illustrated and reviewed in this paper show why general emphasis needs to be placed on the development and adoption of biosurfactants in EOR as a substantial contribution to a more sustainable and environmentally friendly oil and gas industry.

Plant-based ink properties and storage stability for inkjet printing.

In this sustainability-oriented research, the properties of plant-based inks were evaluated denoting the viscosity range of 8.5 to 10 cP, the relative density of 1.06, conductivity value of 2.51 mS/cm, and the surface tension of 60 mN/m and pH of 4.9 to be most effective for inkjet printing. The changes in these properties to the one-month storage phase are detailed as determined with attenuated total reflectance - Fourier transform infrared spectroscopy, viscometer, and tensiometer. The varied colours of plant-based inks were stable to storage time except for the blue colour ink made from bio indigo herb that displayed agal-like sediments. After the storage phase, the plant-based inks exhibited anti-thixotropic viscosity except for yellow colour plant-based ink demonstrating thixotropic behaviour. High conductivity values of 18.5 and 15.6 mS/Cm were noted for blue and black colour plant-based inks, indicating their potential for constituting conducting inks; however, the conductivity values dropped to 7.5 and 9.5, respectively, after 1 month. The pH and surface tension were found steady during the storage period. The study of the life cycle analysis of plant-based inks is suggested for future work. The significance of this work in developing plant-based inks for inkjet printing of textiles lies in the convergence of sustainability and innovation. Plant-based inks can offer an eco-friendly alternative to traditional synthetic inks that are used currently, which provides a knowledge base for good practises meeting the environmentally conscious in the digital printing of the textile industry. These developed inks from this study can not only reduce the environmental impact but also promote a healthier ecosystem.

Structural changes in layers of lipid mixtures at low surface tensions.

Layers of pulmonary lipids on an aqueous substrate at non-equilibrium conditions can decrease the surface tension of water to quite low values. This is connected with different relaxation processes occurring at the interface and the associated changes in the surface layer structure. Results of measurements by the combination of methods like surface rheology, ellipsometry, Brewster angle microscopy, and IRRAS for spread layers of lipid mixtures open a possibility to specify the dynamics of structural changes at conditions close to the physiological state. At sufficiently low surface tension values (below 5 mN/m) significant changes in the ellipsometric signal were observed for pure DPPC layers, which can be related to a transition from 2D to 3D structures caused by the layer folding. The addition of other lipids can accelerate the relaxation processes connected with squeezing-out of molecules or multilayer stacks formation hampering thereby a decrease of surface tension down to low values corresponding to the folding of the monolayer.

Quantifying both viscoelasticity and surface tension: Why sharp tips overestimate cell stiffness.

Quantifying the mechanical properties of cells is important to better understand how mechanics constrain cellular processes. Furthermore, because pathologies are usually paralleled by altered cell mechanical properties, mechanical parameters can be used as a novel way to characterize the pathological state of cells. Key features used in models are cell tension, cell viscoelasticity (representing the average of the cell bulk), or a combination of both. It is unclear which of these features is the most relevant or whether both should be included. To clarify this, we performed microindentation experiments on cells with microindenters of various tip radii, including micrometer-sized microneedles. We obtained different cell-indenter contact radii and measured the corresponding contact stiffness. We derived a model predicting that this contact stiffness should be an affine function of the contact radius and that, at vanishing contact radius, the cell stiffness should be equal to the cell tension multiplied by a constant. When microindenting leukocytes and both adherent and trypsinized adherent cells, the contact stiffness was indeed an affine function of the contact radius. For leukocytes, the deduced surface tension was consistent with that measured using micropipette aspiration. For detached endothelial cells, agreement between microindentation and micropipette aspiration was better when considering these as only viscoelastic when analyzing micropipette aspiration experiments. This work suggests that indenting cells with sharp tips but neglecting the presence of surface tension leads to an effective elastic modulus whose origin is in fact surface tension. Accordingly, using sharp tips when microindenting a cell is a good way to directly measure its surface tension without the need to let the viscoelastic modulus relax.

Effect of mechanical stresses on viral capsid disruption during droplet formation and drying.

Identification of the mechanisms by which viruses lose activity during droplet formation and drying is of great importance to understanding the spread of infectious diseases by virus-containing respiratory droplets and to developing thermally stable spray dried live or inactivated viral vaccines. In this study, we exposed suspensions of baculovirus, an enveloped virus, to isolated mechanical stresses similar to those experienced during respiratory droplet formation and spray drying: fluid shear forces, osmotic pressure forces, and surface tension forces at interfaces. DNA released from mechanically stressed virions was measured by SYBR Gold staining to quantify viral capsid disruption. Theoretical estimates of the force exerted by fluid shear, osmotic pressures and interfacial tension forces during respiratory droplet formation and spray drying suggest that osmotic and interfacial stresses have greater potential to mechanically destabilize viral capsids than forces associated with shear stresses. Experimental results confirmed that rapid changes in osmotic pressure, such as those associated with drying of virus-containing droplets, caused significant viral capsid disruption, whereas the effect of fluid shear forces was negligible. Surface tension forces were sufficient to provoke DNA release from virions adsorbed at air-water interfaces, but the extent of this disruption was limited by the time required for virions to diffuse to interfaces. These results demonstrate the effect of isolated mechanical stresses on virus particles during droplet formation and drying.

A multi-scale approach to arabinoxylan-based emulsions: From molecular features, interfacial properties to emulsion behaviors.

Arabinoxylan (AX) is well-known for its emulsification and beneficial biological activity, but the roles of AX's molecular features and interfacial properties in AX-based emulsion behaviors were unknown. We first used a multi-scale approach to correlate molecular, interfacial, droplet characteristics, and bulk emulsion of AXs from corn and wheat bran (CAXs and WAXs). Our results showed that among CAXs and WAXs solution (1 %, 2 % and 3 %, w/v), 0.25 M NaOH-treated CAX and WAX showed smaller particle sizes (493 nm and 8621 nm), lower interfacial tension and stronger interfacial layer, whose emulsion exhibited smaller initial droplets (541 nm and 660 nm) and better stability. Moreover, WAXs had bigger particle sizes, lower interfacial tension and stronger interfacial layer than CAXs, but CAXs exhibited better emulsifying and emulsion-stabilizing properties than WAXs. There is a satisfactory correlation among CAXs' or WAXs' molecular features, interfacial properties and emulsion behaviors. However, a good correlation from different grains AXs cannot be established.

Role of the pea protein aggregation state on their interfacial properties.

HYPOTHESIS: Plant protein ingredients from similar sources can vary in functionality not only because of compositional differences, but also because of differences in their structure depending on their processing history. It is essential to understand these distinctions to develop novel food emulsion using plant proteins. It is hypothesized that differing interfacial properties can be attributed to their structures, aggregation, and colloidal states. EXPERIMENTS: The adsorption behavior of a commercial protein isolate, homogenized or non-homogenized, was compared to a mildly extracted isolate to evaluate the effect of aggregation state and structural differences. After characterization of the particle size and protein composition, the interfacial properties were compared. FINDINGS: Atomic force microscopy provided evidence of interfaces packed with protein oligomers regardless of the treatment. Differences in adsorption kinetics and interfacial shear rheology depending on oil polarity suggested different interfacial structures. A polydisperse mixture of protein oligomers resulted in increased rearrangements and protein-protein interactions at the interface. Homogenization of commercial proteins resulted in a lower interfacial tension and less elastic interfaces compared to those of native proteins due to the presence of larger aggregates. This study highlights how the interfacial properties can be related to the protein aggregation state resulting from differences in processing history.

Pulmonary Surfactant Homeostasis Dysfunction Mediates Multiwalled Carbon Nanotubes Induced Lung Fibrosis via Elevating Surface Tension.

Multiwalled carbon nanotubes (MWCNTs) have been widely used in many disciplines and raised great concerns about their negative health impacts, especially environmental and occupational exposure. MWCNTs have been reported to induce fibrotic responses; however, the underlying mechanisms remain largely veiled. Here, we reported that MWCNTs inhalation induced lung fibrosis together with decreased lung compliance, increased elastance in the mice model, and elevated surface tension in vitro. Specifically, MWCNTs increased surface tension by impairing the function of the pulmonary surfactant. Mechanistically, MWCNTs induced lamellar body (LB) dysfunction through autophagy dysfunction, which then leads to surface tension elevated by pulmonary surfactant dysfunction in the context of lung fibrosis. This is a study to investigate the molecular mechanism of MWCNTs-induced lung fibrosis and focus on surface tension. A direct mechanistic link among impaired LBs, surface tension, and fibrosis has been established. This finding elucidates the detailed molecular mechanisms of lung fibrosis induced by MWCNTs. It also highlights that pulmonary surfactants are expected to be potential therapeutic targets for the prevention and treatment of lung fibrosis induced by MWCNTs.

The influence of selected polymers on the surface tension of solutions developed for the preparation of eye drops.

BACKGROUND: Many substances are used to increase the viscosity of eye drops and reduce their surface tension. Their function is to prolong the persistence of the product on the surface of the eyeball and to increase the bioavailability of the pharmacologically active ingredient. OBJECTIVES: To investigate the surface tension of substances added to the eye drops, with the main aim of modulating properties of the preparation. MATERIAL AND METHODS: Five substances contained in solutions proposed for the development of eye drops were studied: sodium hyaluronate macromolecular (H-Na W), sodium hyaluronate ultramolecular (H-Na UM), hyaluronic acid 4% (K-H), methylcellulose (MC), and polyacrylic acid (PA). The main method was to study the surface tension using the du Noüy ring tensiometer. RESULTS: The research presented in this paper shows the various effects of different eye drop ingredients on the surface tension of the solutions. The surface tension values of PA solutions are in the range of 48.89-56.03 mN/m, of MC in the range of 68.94-89.32 mN/m, of K-H 54.54-65.66 mN/m, of H-Na UM 67.18-70.97 mN/m, and of H-Na W 67.09-71.73 mN/m. CONCLUSIONS: The use of different polymers affects the surface tension of model solutions proposed for use in ophthalmic preparations. Compounds containing carboxyl groups and anionic polymers have a similar effect on reducing the surface tension of the solution as classical surfactant compounds.

Effect of the Interfacial Tension on the Stability of Silica Stabilized Pickering Emulsions near the Lower Critical Solution Temperature of 2,6-Lutidine - Water Mixtures.

In this paper, the kinetic stability of Pickering emulsions stabilized by spherical silica particles (100 nm in diameter) was examined in the water - 2,6-lutidine mixture. In the close vicinity of the lower critical solution temperature, Pickering emulsions were unstable due to the ultra-low liquid-liquid interfacial tension but increased their stability with increasing the temperature. In this system, the interfacial tension obeys universal scale law and can be tuned by temperature without adding any surface-active agents. Owing to this unique feature, we elucidated the relation between the interfacial tension and the stability of Pickering emulsions.

Aggregate Size Modulates the Oil/Water Interfacial Behavior of Myofibrillar Proteins: Toward the Thicker Interface Film and Disulfide Bond.

Myofibrillar protein (MP) aggregate models have been established to elucidate the correlation between their aggregate sizes and interfacial properties. The interfacial layer thickness was measured by the polystyrene latex method and quartz crystal microbalance with dissipation measurement. Interfacial conformations were then characterized in situ (front-surface fluorescence spectroscopy) and ex situ (reactive sulfhydryl group and secondary structure measurement following MP displacement). The viscoelasticity of the interfacial film and its resistance to surfactant-induced competitive displacement were reflected by the dilatational rheology and dynamic interfacial tension with the bulk phase exchange. Finally, we compared the findings of competitive displacement before/after adding a sulfhydryl-blocking agent, N-ethylmaleimide, to highlight the role of S-S linkage on interfacial film formation and stability. We substantiated that the aggregate size of the MP governed their interfacial properties. Small-sized aggregates exhibited more ordered secondary structures on the oil-water interface, which was conducive to the adsorption ratio of the protein and the adsorption dynamics. Although larger aggregates lowered the diffusion rate during interfacial film formation, they allowed the thicker and more viscoelastic interfacial film to be constructed afterward through more disulfide bond formation, resulting in greater resistance to surfactant-induced competitive displacement.

Pulmonary Surfactant: A Mighty Thin Film.

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

Surface tension measurement and calculation of model biomolecular condensates.

The surface tension of liquid-like protein-rich biomolecular condensates is an emerging physical principle governing the mesoscopic interior organisation of biological cells. In this study, we present a method to evaluate the surface tension of model biomolecular condensates, through straighforward sessile drop measurements of capillary lengths and condensate densities. Our approach bypasses the need for characterizing condensate viscosities, which was required in previously reported techniques. We demonstrate this method using model condensates comprising two mutants of the intrinsically disordered protein Ddx4N. Notably, we uncover a detrimental impact of increased protein net charge on the surface tension of Ddx4N condensates. Furthermore, we explore the application of Scheutjens-Fleer theory, calculating condensate surface tensions through a self-consistent mean-field framework using Flory-Huggins interaction parameters. This relatively simple theory provides semi-quantitative accuracy in predicting Ddx4N condensate surface tensions and enables the evaluation of molecular organisation at condensate surfaces. Our findings shed light on the molecular details of fluid-fluid interfaces in biomolecular condensates.