Membrane Deformation Research Articles

Microscale and Macroscale Deformation Behavior of Electrospun Polymeric Nanofiber Membranes Using In Situ SEM during Mechanical Testing

Electrospun nanofiber membranes show high potential in various application fields (e.g., filtration, catalysis, and sensing). Nevertheless, knowledge of the mechanical behavior, and more specifically, the deformation of nanofiber membranes is still limited today which can complicate the appliance of nanofiber membranes in applications where they are mechanically loaded. In this paper, we, therefore, analyzed the mechanical behavior of polymeric nanofiber membranes with different fiber orientations (random and aligned) extensively. Polyamide 6 was used as a representative reference polymer for proof-of-concept. Mechanical tests show that all membranes have a coherent deformation behavior at the macroscale up to the point of fracture. Large variations in stiffness, ultimate strength, and ultimate strain were observed between membranes with different fiber orientations (Random: E-mod: 370 ± 34 MP; UTS: 38.5 ± 6.0 MPa; εmax: 30.0 ± 2.8%; Parallel aligned: E-mod: 753 ± 11 MPa; UTS: 55.4 ± 0.8 MPa; εmax: 12.0 ± 0.1%; Perpendicular aligned: E-mod: 24.1 ± 3.7 MPa; UTS:/; εmax: >40%). This shows the versatility and tunability of the mechanical behavior of these nanofiber membranes. At the microscale, the fibrous structure results in deformation mechanisms that resist failure formation and progression when the membrane is mechanically loaded. This results in a high fracture resistance, even for pre-damaged membranes. Realignment of the fibers along the loading direction causes crack tip blunting, locally reinforcing the membrane.

Ultrathin Conformable Electronic Tattoo for Tactile Sensations

AbstractConformable electronics has emerged in recent years as an innovative research field and the ability of conformable devices to monitor human physiological signals has been extensively explored. Therefore, in this study, the possibility of using conformable electronics as active devices capable of providing stimuli to the human body is investigated. In particular, a new approach is proposed to elicit tactile sensations on human skin using an operating principle based on the generation of localized heat in correspondence with a closed volume of air. This latter consequently expands causing the deformation of a thin membrane. The use of fast prototyping fabrication techniques, i.e., inkjet printing, and commercially available materials, i.e., transfer tattoo paper, allow the device to be produced quickly and easily transferred on the target substrate. Despite the ultrathin thickness (few micrometers), it is possible to observe forces and displacements thanks to localized heating at very low working powers (<300 mW). A pilot test on a voluntary subject demonstrates how it is possible to discriminate the tactile sensation elicited by the active tattoo device. While the working principle on a single taxel is demonstrated, these results show the potential of the new approach for developing wearable tactile displays.

Exploring the impact of ultrasound on antibiotic-resistant bacteria inactivation in the sulfidated zero valent iron/persulfate system

Antibiotic resistance poses huge challenge on human beings. In this study, we evaluated the removal of antibiotic-resistant E. coli and antibiotic-resistant genes through sulfidated zero valent iron activated persulfate system under ultrasound (33 kHz, 40 W). In the proposed system, the inactivation efficiency was significantly improved, 7.8 log AR E. coli were inactivated in 30 min. And antibiotic-resistant genes (ampC and TetB) were also removed after treatment by the system. Impressively, a switch in the AR E. coli decay model from pseudo second order kinetics (R2 = 0.969) to first order kinetics (R2 = 0.981) was found with the introduction of ultrasound. Ultrasound changes in cellular and S-ZVI/PDS reaction processes are the main reason. Ultrasound converted the system from a heterogeneous process to a homogeneous process. Fe2+ played the main role in the radical generation and the fate of Fe2+ was explored by XPS and XRD. Not only sulfidation promoted the release and regeneration of Fe2+, but also ultrasound accelerated the migration of Fe2+ from the S-ZVI surface to the solution. Reactive oxygen species (OH·, SO4-·, and O2-·) were the vital reasons for antibiotic-resistant E. coli elimination. TEM and FTIR analyses illustrated the changes in cell structure and substance after treatment. Ultrasound boosted cell membrane deformation and rupture which accelerated their inactivation under free radical attack.

Out-of-plane deformability and its coupling with electrostatics in biomembranes

Cell membranes are quasi-bidimensional soft systems formed by multipoles in an ordered array that can be polarized in an electric field. Consequently, electrostatic potentials emerge inside membranes, and membranes respond to external electric fields. From a mechanical perspective, membranes can be easily compressed-expanded, laterally deformed, and curved. Bending is particularly easy, and this kind of deformation translates to changes in the relative positions of the negative and positive charges, leading to strain gradient-induced polarization. Conversely, an external electric field gradient will exert a bending stress that translates to mechanical membrane deformation. These phenomena are described through membrane flexoelectricity. Here, we describe this property in lipid bilayers and cell membranes and summarize the studies in the field with emphasis on the effects promoted by membrane asymmetry.

Single molecule analyses reveal dynamics of Salmonella translocated effector proteins in host cell endomembranes

The facultative intracellular pathogen Salmonella enterica remodels the host endosomal system for survival and proliferation inside host cells. Salmonella resides within the Salmonella-containing vacuole (SCV) and by Salmonella-induced fusions of host endomembranes, the SCV is connected with extensive tubular structures termed Salmonella-induced filaments (SIF). The intracellular lifestyle of Salmonella critically depends on effector proteins translocated into host cells. A subset of effectors is associated with, or integral in SCV and SIF membranes. How effectors reach their subcellular destination, and how they interact with endomembranes remodeled by Salmonella remains to be determined. We deployed self-labeling enzyme tags to label translocated effectors in living host cells, and analyzed their single molecule dynamics. Translocated effectors diffuse in membranes of SIF with mobility comparable to membrane-integral host proteins in endomembranes. Dynamics differ between various effectors investigated and is dependent on membrane architecture of SIF. In the early infection, host endosomal vesicles are associated with Salmonella effectors. Effector-positive vesicles continuously fuse with SCV and SIF membranes, providing a route of effector delivery by translocation, interaction with endosomal vesicles, and ultimately fusion with the continuum of SCV/SIF membranes. This mechanism controls membrane deformation and vesicular fusion to generate the specific intracellular niche for bacterial survival and proliferation.

Dexamethasone and Dexamethasone Phosphate: Effect on DMPC Membrane Models

Dexamethasone (Dex) and Dexamethasone phosphate (Dex-P) are synthetic glucocorticoids with high anti-inflammatory and immunosuppressive actions that gained visibility because they reduce the mortality in critical patients with COVID-19 connected to assisted breathing. They have been widely used for the treatment of several diseases and in patients under chronic treatments, thus, it is important to understand their interaction with membranes, the first barrier when these drugs get into the body. Here, the effect of Dex and Dex-P on dimyiristoylphophatidylcholine (DMPC) membranes were studied using Langmuir films and vesicles. Our results indicate that the presence of Dex in DMPC monolayers makes them more compressible and less reflective, induces the appearance of aggregates, and suppresses the Liquid Expanded/Liquid Condensed (LE/LC) phase transition. The phosphorylated drug, Dex-P, also induces the formation of aggregates in DMPC/Dex-P films, but without disturbing the LE/LC phase transition and reflectivity. Insertion experiments demonstrate that Dex induces larger changes in surface pressure than Dex-P, due to its higher hydrophobic character. Both drugs can penetrate membranes at high lipid packings. Vesicle shape fluctuation analysis shows that Dex-P adsorption on GUVs of DMPC decreases membrane deformability. In conclusion, both drugs can penetrate and alter the mechanical properties of DMPC membranes.

Endocytosis-Like Vesicle Fission Mediated by a Membrane-Expanding Molecular Machine Enables Virus Encapsulation for In Vivo Delivery.

Biological membranes are functionalized by membrane-associated protein machinery. Membrane-associated transport processes, such as endocytosis, represent a fundamental and universal function mediated by membrane-deforming protein machines, by which small biomolecules and even micrometer-size substances can be transported via encapsulation into membrane vesicles. Although synthetic molecules that induce dynamic membrane deformation have been reported, a molecular approach enabling membrane transport in which membrane deformation is coupled with substance binding and transport remains critically lacking. Here, we developed an amphiphilic molecular machine containing a photoresponsive diazocine core (AzoMEx) that localizes in a phospholipid membrane. Upon photoirradiation, AzoMEx expands the liposomal membrane to bias vesicles toward outside-in fission in the membrane deformation process. Cargo components, including micrometer-size M13 bacteriophages that interact with AzoMEx, are efficiently incorporated into the vesicles through the outside-in fission. Encapsulated M13 bacteriophages are transiently protected from the external environment and therefore retain biological activity during distribution throughout the body via the blood following administration. This research developed a molecular approach using synthetic molecular machinery for membrane functionalization to transport micrometer-size substances and objects via vesicle encapsulation. The molecular design demonstrated in this study to expand the membrane for deformation and binding to a cargo component can lead to the development of drug delivery materials and chemical tools for controlling cellular activities.

Multilayered membrane spacer: does it enhance solution mixing?

AbstractThe present review systematically investigates and illustrates the effect of multilayered membrane spacers on the features of fluid dynamics that influence all performance metrics. Multilayer spacers are frequently composed of three sets of filaments (i.e., top, middle, and bottom layers), which has the benefit of increasing mass transfer and decreasing membrane surface fouling when compared to ordinary monolayer (e.g., extruded spacer) and two‐layer spacers. The review found that the multilayer spacer's middle layer disperses primary flow to the thin side spacers placed near the membrane's surfaces. The thin side spacers will then form narrow passageways to keep the solution in situ for as long as mass transfer is achievable. The employment of thin spacers close to the membranes at satisfactory operational conditions (e.g., adequate flow velocity) results in swirling flows and incorporation of transverse and longitudinal eddies near to the membranes, reducing the boundary layer's width and making the associated ion concentration domain at the membranes much more consistent. The concept and implementation of multilayer geometry in feed channels appears to be promising, since a multilayered spacer can function at a lower maximum flow velocity than normal two‐layer spacers, saving operational energy while minimizing concentration gradients at the membrane surfaces. Furthermore, the multilayer structure's durability and mechanical strength may help to reduce membrane deformation and maintain long processes. Future studies might look at significantly reducing spacer thickness for industrial uses. © 2023 Society of Chemical Industry (SCI).

Determination of elastic parameters of lipid membranes from simulation under varied external pressure.

Many cellular processes such as endocytosis, exocytosis, and vesicle trafficking involve membrane deformations, which can be analyzed in the framework of the elastic theories of lipid membranes. These models operate with phenomenological elastic parameters. A connection between these parameters and the internal structure of lipid membranes can be provided by three-dimensional (3D) elastic theories. Considering a membrane as a 3D layer, Campelo etal. [F. Campelo etal., Adv. Colloid Interface Sci. 208, 25 (2014)10.1016/j.cis.2014.01.018] developed a theoretical basis for the calculation of elastic parameters. In this work we generalize and improve this approach by considering a more general condition of global incompressibility instead of local incompressibility. Crucially, we find an important correction to the theory of Campelo etal., which if not taken into account leads to a significant miscalculation of elastic parameters. With the total volume conservation taken into account, we derive an expression for the local Poisson's ratio, which determines how the local volume changes upon stretching and permits a more precise determination of elastic parameters. Also, we substantially simplify the procedure by calculating the derivatives of the moments of the local tension with respect to stretching instead of calculating the local stretching modulus. We obtain a relation between the Gaussian curvature modulus as a function of stretching and the bending modulus, showing that these two elastic parameters are not independent, as was previously assumed. The proposed algorithm is applied to membranes composed of pure dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), and their mixture. The following elastic parameters of these systems are obtained: the monolayer bending and stretching moduli, spontaneous curvature, neutral surface position, and local Poisson's ratio. It is shown that the bending modulus of the DPPC/DOPC mixture follows a more complex trend than predicted by the classical Reuss averaging, which is often employed in theoretical frameworks.

The small GTPase Sar1, control centre of COPII trafficking.

Sar1 is a small GTPase of the ARF family. Upon exchange of GDP for GTP, Sar1 associates with the endoplasmic reticulum (ER) membrane and recruits COPII components, orchestrating cargo concentration and membrane deformation. Many aspects of the role of Sar1 and regulation of its GTP cycle remain unclear, especially as complexity increases in higher organisms that secrete a wider range of cargoes. This review focusses on the regulation of GTP hydrolysis and its role in coat assembly, as well as the mechanism of Sar1-induced membrane deformation and scission. Finally, we highlight the additional specialisation in higher eukaryotes and the outstanding questions on how Sar1functionsare orchestrated.

Effect of chilling and salinity stress on photosynthetic performance and ultrastructure of chloroplast in faba beans (Vicia faba L.) leaves

Chilling (Ch) and salinity (S) are challenging stresses affecting plant physiology, growth, and productivity. The current study investigated the effects of these two stresses, singly and in combination, on photosynthetic performance and ultrastructure of chloroplast of faba beans (Vicia faba L. Cv. Aspani). Plants were exposed to 3 °C and 120 mM NaCl for 16 h in an optimized soil mixture (sand:clay 2:1) under optimized conditions. Results showed that both Ch and S significantly reduced photosynthetic rates, Fv/Fm, chlorophyll content, stomatal index, and stomatal conductance. Chilling caused changes in chloroplast ultrastructure (swelling, ruptured envelopes, and shrunk lamellae), while salinity caused more deformation of the thylakoid membrane and disorganization of the grana structure. However, there was an antagonistic effect between Ch x S. The tolerance of plant to 120 mM NaCl, in the present study, was improved by exposure to Ch which rather allowed the maintenance of chloroplast ultrastructure and morphology of stomata. Moreover, using SEM and TEM gave an effective insight of the ultrastructural damage in plant cells under stress and helps to consider the underlying mechanisms of stress effects. Our results suggest that Ch mitigates the noxious effect of S on the photosynthetic performance of Vicia faba plants.

A Curved Plate-Flattening Method to Construct the Membrane Strain Distribution

The surface-flattening process has many applications in industries such as shipbuilding. Curved surfaces in the industry are usually formed from flat surfaces, so the target surface needs to be flattened to obtain its corresponding initial shape. In addition, the surface flattening process obtains the inherent strain distribution required in forming. Different forming methods in the plate forming process will produce different membrane deformations, such as shrinkage in the line heating and tensile in the roller forming. Therefore, different surface-flattening methods should be used to obtain the inherent strain distribution suitable for different forming methods. This paper proposes a method to perform the surface flattening using the finite element method and constrain the membrane strain generated in the flattening deformation by modifying the material constitutive relationship. Using a dual modulus material constitutive model in membrane deformation makes the surface more inclined to deform at locations with less stiffness during the flattening process. This method yields predominantly tensile or compressive membrane strain without changing the bending strain. By modifying the material model, this method can control the compressive strain region and the principal strain direction. The results of the proposed method applying to different surface shapes and its application in the surface-forming process are given in this paper.

Enhanced and Stem-Cell-Compatible Effects of Nature-Inspired Antimicrobial Nanotopography and Antimicrobial Peptides to Combat Implant-Associated Infection.

Nature-inspired antimicrobial surfaces and antimicrobial peptides (AMPs) have emerged as promising strategies to combat implant-associated infections. In this study, a bioinspired antimicrobial peptide was functionalized onto a nanospike (NS) surface by physical adsorption with the aim that its gradual release into the local environment would enhance inhibition of bacterial growth. Peptide adsorbed on a control flat surface exhibited different release kinetics compared to the nanotopography, but both surfaces showed excellent antibacterial properties. Functionalization with peptide at micromolar concentrations inhibited Escherichia coli growth on the flat surface, Staphylococcus aureus growth on the NS surface, and Staphylococcus epidermidis growth on both the flat and NS surfaces. Based on these data, we propose an enhanced antibacterial mechanism whereby AMPs can render bacterial cell membranes more susceptible to nanospikes, and the membrane deformation induced by nanospikes can increase the surface area for AMPs membrane insertion. Combined, these effects enhance bactericidal activity. Since functionalized nanostructures are highly biocompatible with stem cells, they make promising candidates for next generation antibacterial implant surfaces.

Get in and get out: Remodeling of the cellular actin cytoskeleton upon HIV-1 infection.

The human immunodeficiency virus type 1 (HIV-1) is an intracellular pathogen whose replication cycle strictly depends on the host cell molecular machinery. HIV-1 crosses twice the plasma membrane, to get in and to get out of the cell. Therefore, the first and the last line of intracellular component encountered by the virus is the cortical actin network. Here, we review the role of actin and actin-related proteins in HIV-1 entry, assembly, budding, and release. We first highlight the mechanisms controlling actin polymerization at the entry site that promote the clustering of HIV-1 receptors, a crucial step for the virus to fuse with the plasma membrane. Then, we describe how actin is transiently depolymerized locally to allow the capsid to cross the actin cortex, before migrating towards the nucleus. Finally, we review the role of several actin-binding proteins in actin remodeling events required for membrane deformation and curvature at the viral assembly site as well as for virus release. Strikingly, it appears that common actin-regulating pathways are involved in viral entry and exit. However, while the role of actin remodeling during entry is well understood, this is not the case during exit. We discuss remaining challenges regarding the actin-dependent mechanisms involved in HIV-1 entry and exit, and how they could be overcome.

Structural Changes of the Interface Material of Scallop Adductor under Ultra-High Pressure

Because of their high nutritional value, the demand for scallops is increasing year by year. In the process of improving people’s living standards, the ready-to-eat characteristics and dry sales characteristics of this product make its shelling process particularly important in the production process. However, the mechanism of ultra-high pressure shelling has not yet been clarified. Therefore, in-depth study of the structural change of the scallop connection interface is of vital importance to explore the mechanism of ultra-high pressure shelling and the development of intelligent equipment from the mechanical point of view. The obturator muscle fibers and the inner surface materials of the shell at the obturator muscle scar of the scallop at 100, 200 and 300 MPa were obtained for Raman spectrum, Fourier-transform infrared spectrum and scanning electron microscopy analysis. The results showed that under the pressure of 200 MPa, the degree of protein denaturation of scallop adductor muscle increased, the elasticity disappeared, and the fiber was stretched; The deformation of the organic plasma membrane connected by the inorganic–organic interface weakens the binding force of the interface material and increases the possibility of the composite interface failure. To sum up, ultra-high pressure can effectively weaken the interface adhesion of scallop organic-inorganic composite materials, and is one of the effective ways of shelling. The research results can provide a basis for the in-depth analysis of ultra-high pressure mechanisms and the development of intelligent equipment, and provide technical support for the realization of ultra-high-pressure industrial production.

Analysis of fluid-structure interaction in a directional permeability membrane in pressure-driven flow

Finite volume and finite element analysis of fluid-structure interaction is performed to understand the behavior of a directional permeability membrane in pressure-driven flow. The membrane is comprised of two flexible porous sheets separated by a spacer. The porous sheets each have a different thickness with pores that are offset from each other. The design allows flow when the thicker sheet is on the high pressure side, but prevents flow if the pressure gradient is reversed. Flow through the membrane is studied for a pressure range of 0.01–0.1 m H2O in forward flow to understand the complex fluid motion and dependence of membrane deformation on sheet thickness, downstream pore diameter, and initial gap between the sheets. In forward flow, maximum mass flow rate of 0.2 g s−1 (or flow rate of 12.024 ml min−1) can be obtained at 0.1 m H2O pressure head. Reverse flow conditions are modeled to study the effect of design parameters on the required closing pressure, indicating that as little as 0.0325 m H2O of pressure head is required for closing.

Dynamic density functional theory of multicomponent cellular membranes

We present a continuum model trained on molecular dynamics (MD) simulations for cellular membranes composed of an arbitrary number of lipid types. The model is constructed within the formalism of dynamic density functional theory and can be extended to include features such as the presence of proteins and membrane deformations. This framework represents a paradigm shift by enabling simulations that can access length scales on the order of microns and time scales on the order of seconds, all while maintaining near fidelity to the underlying MD models. These length and time scales are significant for accessing biological processes associated with signaling pathways within cells. Membrane interactions with RAS, a protein implicated in roughly 30% of human cancers, are considered as an application. Simulation results are presented and verified with MD simulations, and implications of this new capability are discussed.

On the time-dependent mechanics of membranes via the nonlinear finite element method

In this work, the problem of finite generalized and viscoelastic deformation of thin membranes with different geometries, made of incompressible hyperelastic materials, is formulated. The multiplicative decomposition of the deformation gradient tensor into elastic and viscous parts, and making use of dissipation inequality, nonlinear evolution equations for the internal variables of the models are obtained. The mechanical behavior of the dampers is assumed to be linearly viscous. Therefore, the Cauchy-like stress in the dampers is similar to that in Newtonian fluids and includes terms for the hydrostatic pressure and viscosity. The implicit and second-order accurate trapezoidal method is employed for the time integration of the evolution equations. Due to the highly nonlinear governing differential equations including the effects of geometric nonlinearity and viscoelasticity, a nonlinear finite element formulation based on isoparametric elements is developed. The accuracy and performance of the developed formulation and time-dependent solutions are verified by studying several numerical examples. The obtained results are compared with theoretical and experimental data available in the literature. The proposed formulation can appropriately predict the experimental results of viscoelastic membranes for both in-plane and out-of-plane deformations.

Investigation of Pressure Fields Generated by Two Simultaneous Discharges in Liquid Initiated by Wires

The pressure fields generated by two simultaneous discharges have not been investigated on any notable scale for the electrohydraulic impulse forming method. In this study, the synchronicity of two discharges is ensured by the sequential connection of two wires mounted in two spark gaps in a common volume of liquid. The objective is to experimentally confirm the equilibrium of the energies evolved in two spark gaps by means of pressure measurements. In addition, multipoint membrane pressure gauges demonstrated the feasibility of easily recording detailed pressure maps. Based on the membrane deformation mechanism and material strengthening under static and impulse conditions, the processing procedure is further developed so as to achieve better accuracy in the determination of pressure field parameters. The practical equality of the pressure fields on the left and right halves of the flat-loaded area confirms the equality of energies evolved in the two spark gaps. The direct shock waves create zones with the most intensive loading. These results provide a basis for the development of new electrohydraulic technologies involving the application of two simultaneous discharges with equal energy and pressure parameters.

Complex multivalent protein interactions involving endophilin, lamellipodin and VASP regulate membrane shaping phenomena and actin assembly.

Lamellipodin (LPD) is a peripheral membrane protein that plays an initiatory role in endocytic pathways such as Fast endophilin mediated endocytosis by the recruitment of Endophilin, and regulatory roles in lamellipodia and filopodia by recruiting ena/VASP proteins. The processes of endocytosis and cellular motility depend on actin polymerization and involve inward and outward deformation of the plasma membrane respectively. The question thus can be asked: how does LPD recruit its binding partners, the curvature generating BAR protein endophilin and the actin polymerase VASP, to specifically trigger the aforementioned phenomena and concomitant directional membrane remodelling? In this thrust, we probe the complex multi-protein interplay by reconstituting these interactions in vitro. First, we show that VASP and LPD associate multivalently to undergo liquid like phase separation, a fundamental physical process ubiquitously observed in biology. We find that actin polymerization is exclusively initiated in the LPD-VASP rich clusters, and that elongating filaments deform the clusters resulting in local protein reorganization and the formation of large scale VASP-LPD facilitated actin networks. Our observation along with the fact that growing actin filaments deform the adjacent lipid bilayer, introduces a new intermediate step for membrane remodelling, a protein-protein phase separation mediated actin network formation. Next, we investigated the role of Endophilin in the above-mentioned system. We have previously shown that endophilin and LPD interact multivalently in the priming of FEME patches. Here we find that endophilin participates in VASP-LPD phase separation and influences actin filament morphology and connectivity. We thus anticipate that the initiation and the direction of curvature generation are governed by complex multivalent interactions that regulate actin polymerization.