Membrane Elastic Modulus Research Articles

Enhancing the Cu (II) removal in water using functional hybrid membranes

This work developed composite and hybrid membranes of poly(butylene adipate-co-terephthalate) (PBAT) with nanocurcumin (NC) and/or cloisite 20A (C20A). The dispersed phases were characterized by DLS, ζ potential, XRD, SEM, and FTIR, while XRD, SEM, FTIR, mechanical properties, contact angle, and copper sorption evaluated the composite membranes. DLS analysis indicated that the dispersed phases present a nanometric size distribution; ζ potential measurements showed low electrostatic stability, explaining the agglomeration effects observed. Pure PBAT membranes presented macro-pores throughout their structure, which showed a slight size reduction with the inclusion of NC and C20A. The membrane's mechanical performance was affected by the presence of the pores that acted as stress-concentrating defects, and the inclusion of the dispersed phases increased the membrane elastic modulus and tensile strength, especially for PBAT/0.5%C20A with values 18.7 and 8.9% higher than those of pure PBAT, respectively. Composite membranes also showed a hydrophilic nature with all the contact angle measurements lower than 90º. The sorption tests using a high-concentration copper solution (1000 mg/L) showed that the composite membranes achieved a removal of around 25%. These results highlighted the development of new eco-friendly membranes using NC and C20A as dispersed phases with the potential to remove toxic elements from water.

Universal contact stiffness of elastic solids covered with tensed membranes and its application in indentation tests of biological materials.

The inherent membrane tension of biological materials could vitally affect their responses to contact loading but is generally ignored in existing indentation analysis. In this paper, the authors theoretically investigate the contact stiffness of axisymmetric indentations of elastic solids covered with thin tensed membranes. When the indentation size decreases to the same order as the ratio of membrane tension to elastic modulus, the contact stiffness accounting for the effect of membrane tension becomes much higher than the prediction of conventional contact theory. An explicit expression is derived for the contact stiffness, which is universal for axisymmetric indentations using indenters of arbitrary convex profiles. On this basis, a simple method of analysis is proposed to estimate the membrane tension and elastic modulus of biological materials from the indentation load-depth data, which is successfully applied to analyze the indentation experiments of cells and lungs. This study might be helpful for the comprehensive assessment of the mechanical properties of soft biological systems. STATEMENT OF SIGNIFICANCE: This paper highlights the crucial effect of the inherent membrane tension on the indentation response of soft biomaterials, which has been generally ignored in existing analysis of experiments. For typical indentation tests on cells and organs, the contact stiffness can be twice or higher than the prediction of conventional contact model. A universal expression of the contact stiffness accounting for the membrane tension effect is derived. On this basis, a simple method of analysis is proposed to abstract the membrane tension of biomaterials from the experimentally recorded indentation load-depth data. With this method, the elasticity of soft biomaterials can be characterized more comprehensively.

Nano-scale "sticky tape" stabilizes open-edge boundary conditions in MD simulations of asymmetric membranes.

Recent advances in membrane biophysics have driven deeper investigations into lipid bilayer asymmetry and its biological implications. Molecular dynamics simulations of asymmetric membranes have recently highlighted the potential role of differential stress in regulating membrane elastic moduli and phase behavior, in addition to the already known composition asymmetries. The vast majority of MD simulations of membranes are flat, tensionless, fully periodic geometries, which artificially suppress membrane bending even in the presence of a non-vanishing net torque. In order to allow a membrane to relax to its true equilibrium curvature state determined by a sensitive balance of monolayer area strains and spontaneous curvatures, it is desirable to simulate with periodicity in only one direction with open edges along the other. However, lipid flip-flop over the open edges rapidly destroys any membrane asymmetry. We present a technique for maintaining membrane asymmetry with open edges by applying “sticky tape” to the membrane edges parallel to the direction of periodicity to prevent flip-flop. By varying lipid number asymmetry at fixed monolayer compositions, this free-curvature technique can be used to determine the voluntarily flat state of an asymmetric membrane, which can be transferred to fully periodic conditions for production. By monitoring membrane curvature as a function of number asymmetry in composition-symmetric systems, monolayer spontaneous curvatures can be deduced without the need to calculate lateral stress profiles and relate their moments to continuum theory. Importantly, this method does not significantly impact the structure of the fluid lipid phase in the bulk. We present this technique using the ultra-coarse-grained Cooke lipid model, but the concept is easily transferable to more finely-resolved models, allowing for simultaneously area- and curvature-relaxed membrane simulations.

An analytical model describing the mechanics of erythrocyte membrane wrapping during active invasion of a plasmodium falciparum merozoite

The invasion of a merozoite into an erythrocyte by membrane wrapping is a hallmark of malaria pathogenesis. The invasion involves biomechanical interactions whereby the merozoite exerts actomyosin-based forces to push itself into and through the erythrocyte membrane while concurrently inducing biochemical damage to the erythrocyte membrane. Whereas the biochemical damage process has been investigated, the detailed mechanistic understanding of the invasion mechanics remains limited. Thus, the current study aimed to develop a mathematical model describing the mechanical factors involved in the merozoite invasion into an erythrocyte and explore the invasion mechanics.A shell theory model was developed comprising constitutive, equilibrium and governing equations of the deformable erythrocyte membrane to predict membrane mechanics during the wrapping of an entire non-deformable ellipsoidal merozoite. Predicted parameters include principal erythrocyte membrane deformations and stresses, wrapping and indentation forces, and indentation work. The numerical investigations considered two limits for the erythrocyte membrane deformation during wrapping (4% and 51% areal strain) and erythrocyte membrane phosphorylation (decrease of membrane elastic modulus from 1 to 0.5 kPa).For an intact erythrocyte, the maximum indentation force was 1 and 8.5 pN, and the indentation work was 1.92 × 10−18 and 1.40 × 10−17 J for 4% and 51% areal membrane strain. Phosphorylation damage in the erythrocyte membrane reduced the required indentation work by 50% to 0.97 × 10−18 and 0.70 × 10−17 J for 4% and 51% areal strain.The current study demonstrated the developed model's feasibility to provide new knowledge on the physical mechanisms of the merozoite invasion process that contribute to the invasion efficiency towards the discovery of new invasion-blocking anti-malaria drugs.

Preparation and characterization of forward osmosis cellulose acetate butyrate/OH‐functionalized multiwalled carbon nanotube membrane for the concentration of bitter orange juice

AbstractAs an essential process in food industry, fruit dewatering should have the least impact on the nutritional values of the product. In this research, bitter orange juice was concentrated via the forward osmosis (FO) process for the first time. For this purpose, cellulose acetate butyrate (CAB)/OH‐functionalized multiwalled carbon nanotubes (FMWCNTs) membranes were prepared using various nanofiller concentrations. The obtained membranes were characterized in terms of their morphology, porosity, water contact angle, chemical structure, tensile properties, and pure water flux. During the FO process, NaCl solution was applied as the draw solution (DS), and the concentration of NaCl was varied (1.2, 2.2, and 4.2 M) to assess its effect on the process performance. Increasing FMWCNTs loading in the casting solution up to 0.3 wt% boosted the membrane porosity, hydrophilicity, elastic modulus, and pure water flux. The CAB membrane incorporated with 0.3 wt% nanofiller and the DS with 4.2 M NaCl concentration represented the highest water flux (29.93 L/m2h) in the FO experiment and provided the maximum turbidity (1545 NTU) and viscosity (4.64 cP) of the treated feed. According to the obtained results, the developed CAB/FMWCNTs membrane proved promising in the FO concentration of fruit juice.Practical ApplicationsBitter orange juice was concentrated via the FO process using the developed CAB/OH‐FMWCNTs membranes. According to the results, water flux, and thus the dewatering efficiency increased and reached its highest value using the CAB membrane incorporated with 0.3% FMWCNTs. Since membrane processes operate at low temperatures and do not deteriorate the concentrate quality, FO concentration of bitter orange juice using the membrane modified in this study can be a superior alternative to the conventional thermal methods.

The forewing of a black cicada Cryptotympana atrata (Hemiptera, Homoptera: Cicadidae): Microscopic structures and mechanical properties.

Insects in nature flap their wings to generate lift force and driving torque to adjust their attitude and control stability. An insect wing is a biomaterial composed of flexible membranes and tough veins. In this paper, we study the microscopic structures and mechanical properties of the forewing of the black cicada, Cryptotympana atrata. The thickness of the wing membranes and the diameter of veins varied from the wing root to the tip. The thickness of the wing membranes ranged from 6.0 to 29.9μm, and the diameter of the wing veins decreased in a gradient from the wing root to the tip, demonstrating that the forewing of the black cicada is a nonuniform biomaterial. The elastic modulus of the membrane near the wing root ranged from 4.45 to 5.03 GPa, which is comparable to that of some industrial membranes. The microstructure of the wing vein exhibited a hollow tubular structure with flocculent structure inside. The "fresh" sample stored more water than the "dry" sample, resulting in a significant difference in the elastic modulus between the fresh and dried veins. The different membrane thicknesses and elastic moduli of the wing veins near the root and tip resulted in varied degrees of deformation on both sides of the flexion line of the forewing during twisting. The measurements of the forewing of the cicada may serve as a guide for selecting airfoil materials for the bionic flapping-wing aircraft and promote the design and manufacture of more durable bionic wings in the future. RESEARCH HIGHLIGHTS: The distribution of the wing vein diameter and the wing membrane thickness indicated that the forewing of Cryptotympana atrata is composed of heterogeneous materials. The wing membrane and the outer wall of the wing vein are the layered structure with multilayer fibers, which has a great significance for improving the ability of the forewing to sustain aerodynamic loads. The elastic modulus of the wing membrane near the wing root is in the range of 4.45-5.03GPa, which is comparable to that of membranes manufactured by industries. This is a suitable reference for selecting materials for making bionic aircraft wings. We proved that the elastic moduli of the "fresh" and "dry" wing veins differ greatly compared with those of the wing membrane. Because the wing vein microstructure exhibits an internal hollow tubular structure with flocculent structure inside, the "fresh" sample stores more water than the "dry" sample. The wing membrane near the wing root is thicker and reinforced by the main wing vein with a high elastic modulus. This renders the region near the wing root difficult to deform. The membrane far from the wing root is thinner and the elastic modulus of the nearby wing veins is smaller, making them more flexible.

Experimental study on the behaviour of hybrid fibre reinforced polymer–timber thin-walled Cee section columns

Hybrid fibre-reinforced polymer (FRP)-timber (HFT) think-walled structural members are a novel structural concept developed as a sustainable alternative to the steel and aluminium thin-walled structural members. HFT structures are made by combining thin-timber veneers with fibre reinforced polymer composites. Preliminary studies on HFT structures have shown promising results. However, studies into HFT structural members are still at a very early stage. This study aims to investigate the effects of fibre type, manufacturing pressure, and specimen length on the behaviour of HFT Cee section columns. Three different fibre types, namely glass FRP, natural FRP and natural FRP mat were used in the investigation, while two different manufacturing pressures, 0.1 MPa and 1 MPa were also considered. Two different specimen lengths, 280 mm and 1000 mm were considered in the investigation. In total thirty-three specimens were manufactured and tested under axial compression. In addition, material coupon tests were also carried out to determine the tensile and flexural properties of the laminates. Both membrane and flexural elastic modulus was found to increase with the manufacturing pressure. All the Cee section columns tested failed due to local buckling. Addition of FRP was found to significantly increase the load carrying capacity of the pure timber Cee section columns. HFT Cee section columns made using natural FRP mat were found to provide the highest load carrying capacity. HFT Cee section columns manufactured under 1 MPa pressure were found to perform better than the similar columns manufactured under 0.1 MPa pressure. HFT sections were also found to have a higher weight specific load capacity than similar ultra-thin-walled steel Cee section columns.

A Bioinspired in vitro Lung Model to Study Particokinetics of Nano-/Microparticles Under Cyclic Stretch and Air-Liquid Interface Conditions.

Evolution has endowed the lung with exceptional design providing a large surface area for gas exchange area (ca. 100 m2) in a relatively small tissue volume (ca. 6 L). This is possible due to a complex tissue architecture that has resulted in one of the most challenging organs to be recreated in the lab. The need for realistic and robust in vitro lung models becomes even more evident as causal therapies, especially for chronic respiratory diseases, are lacking. Here, we describe the Cyclic In VItro Cell-stretch (CIVIC) “breathing” lung bioreactor for pulmonary epithelial cells at the air-liquid interface (ALI) experiencing cyclic stretch while monitoring stretch-related parameters (amplitude, frequency, and membrane elastic modulus) under real-time conditions. The previously described biomimetic copolymeric BETA membrane (5 μm thick, bioactive, porous, and elastic) was attempted to be improved for even more biomimetic permeability, elasticity (elastic modulus and stretchability), and bioactivity by changing its chemical composition. This biphasic membrane supports both the initial formation of a tight monolayer of pulmonary epithelial cells (A549 and 16HBE14o−) under submerged conditions and the subsequent cell-stretch experiments at the ALI without preconditioning of the membrane. The newly manufactured versions of the BETA membrane did not improve the characteristics of the previously determined optimum BETA membrane (9.35% PCL and 6.34% gelatin [w/v solvent]). Hence, the optimum BETA membrane was used to investigate quantitatively the role of physiologic cyclic mechanical stretch (10% linear stretch; 0.33 Hz: light exercise conditions) on size-dependent cellular uptake and transepithelial transport of nanoparticles (100 nm) and microparticles (1,000 nm) for alveolar epithelial cells (A549) under ALI conditions. Our results show that physiologic stretch enhances cellular uptake of 100 nm nanoparticles across the epithelial cell barrier, but the barrier becomes permeable for both nano- and micron-sized particles (100 and 1,000 nm). This suggests that currently used static in vitro assays may underestimate cellular uptake and transbarrier transport of nanoparticles in the lung.

Modeling actuation and sensing in ionic polymer metal composites by electrochemo-poromechanics

Ionic polymer metal composites (IPMCs) consist of an electroactive polymeric membrane plated with metal electrodes. They hold promise as actuators and sensors for soft robotics and biomedical applications. Their capabilities ensue from the motion, within the membrane, of a fluid phase consisting of ions dispersed in a solvent. Toward a thorough understanding of IPMC multiphysics, we propose a large deformation theory combining electrochemistry and poromechanics. Namely, we modify the theory recently developed by Porfiri’s group by introducing the transport of the solvent, whose redistribution determines the volumetric deformation of the fluid-saturated membrane, and we further account for the cross-diffusion of solvent and ions. In actuation, the imposed voltage drop across the electrodes triggers ion migration, such that the solvent is transported toward the cathode by electro-osmosis. This determines the initial bending toward the anode; then, back-relaxation occurs because of both the solvent counter-diffusion and the asymmetric redistribution of ions near the electrodes. In short-circuit sensing, the applied load triggers solvent motion, such that ions are mainly transported toward the cathode by convection with the solvent. This determines charge accumulation; then, ion counter-diffusion leads to a decrease of the charge stored at the electrodes. We demonstrate that these behaviors can be predicted by the proposed theory on the basis of relevant finite element benchmarks. Additionally, our analysis encompasses the assessment of the role of the membrane elastic moduli in the counter-diffusion of solvent and ions in IPMC actuation and sensing.

Soft Matter Mechanics and the Mechanisms Underpinning the Infrared Vision of Snakes

Summary Pit-bearing snakes (vipers, pythons, and boas) have the extraordinary ability to “see” and accurately locate their prey and predators in total darkness. These animals use the infrared radiation emanating from objects that are warmer relative to the background environment to form a thermal image. Although enormous progress has been made to identify the key physiological features that enable the infrared vision of these snakes and a few other animals, the precise thermoelectric transduction mechanism that mediates the conversion of infrared heat to processable electrical signals has remained elusive. In this work, we quantitatively outline how cells in the snake's pit membrane organ act as apparent pyroelectric materials and convert infrared radiation into electrical signals. Despite the exceptional simplicity of our proposed mechanism and model, we are able to explain many central experimental results pertaining to the transduction process.

Double-mode relaxation of highly deformed anisotropic vesicles.

Lipid vesicles are known to undergo complex conformational transitions, but it remains challenging to systematically characterize nonequilibrium membrane dynamics in flow. Here, we report the direct observation of anisotropic vesicle relaxation from highly deformed shapes using a Stokes trap. Vesicle shape relaxation is described by two distinct characteristic timescales governed by the bending modulus and membrane tension. Interestingly, the fast double-mode timescale is found to depend on vesicle deflation or reduced volume. Experimental results are well described by a viscoelastic model of a deformed membrane. Overall, these results show that vesicle relaxation is governed by an interplay between membrane elastic moduli, surface tension, and vesicle deflation.

Membrane Thinning Induces Sorting of Lipids and the Amphipathic Lipid Packing Sensor (ALPS) Protein Motif.

Heterogeneities (e.g., membrane proteins and lipid domains) and deformations (e.g., highly curved membrane regions) in biological lipid membranes cause lipid packing defects that may trigger functional sorting of lipids and membrane-associated proteins. To study these phenomena in a controlled and efficient way within molecular simulations, we developed an external field protocol that artificially enhances packing defects in lipid membranes by enforcing local thinning of a flat membrane region. For varying lipid compositions, we observed strong thinning-induced depletion or enrichment, depending on the lipid's intrinsic shape and its effect on a membrane's elastic modulus. In particular, polyunsaturated and lysolipids are strongly attracted to regions high in packing defects, whereas phosphatidylethanolamine (PE) lipids and cholesterol are strongly repelled from it. Our results indicate that externally imposed changes in membrane thickness, area, and curvature are underpinned by shared membrane elastic principles. The observed sorting toward the thinner membrane region is in line with the sorting expected for a positively curved membrane region. Furthermore, we have demonstrated that the amphipathic lipid packing sensor (ALPS) protein motif, a known curvature and packing defect sensor, is effectively attracted to thinner membrane regions. By extracting the force that drives amphipathic molecules toward the thinner region, our thinning protocol can directly quantify and score the lipid packing sensing of different amphipathic molecules. In this way, our protocol paves the way toward high-throughput exploration of potential defect- and curvature-sensing motifs, making it a valuable addition to the molecular simulation toolbox.

Probing Multidimensional Mechanical Phenotyping of Intracellular Structures by Viscoelastic Spectroscopy.

Mechanical phenotyping of complex cellular structures gives insight into the process and function of mechanotransduction in biological systems. Several methods have been developed to characterize intracellular elastic moduli, while direct viscoelastic characterization of intracellular structures is still challenging. Here, we develop a needle tip viscoelastic spectroscopy method to probe multidimensional mechanical phenotyping of intracellular structures during a mini-invasive penetrating process. Viscoelastic spectroscopy is determined by magnetically driven resonant vibration (about 15 kHz) with a tiny amplitude. It not only detects the unique dynamic stiffness, damping, and loss tangent of the cell membrane-cytoskeleton and nucleus-nuclear lamina but also bridges viscoelastic parameters between the mitotic phase and interphase. Self-defined dynamic mechanical ratios of these two phases can identify two malignant cervical cancer cell lines (HeLa-HPV18+, SiHa-HPV16+) whose membrane or nucleus elastic moduli are indistinguishable. This technique provides a quantitative method for studying mechanosensation, mechanotransduction, and mechanoresponse of intracellular structures from a dynamic mechanical perspective. This technique has the potential to become a reliable quantitative measurement method for dynamic mechanical studies of intracellular structures.

Understanding membrane remodelling initiated by photosensitized lipid oxidation

In this review, we describe how photooxidation changes membrane properties that can ultimately lead to permanent membrane damage. Lipid photooxidation occurs in the presence of reactive oxygen species such as singlet oxygen and by direct reactions of lipids with a photosensitizer in the excited state. Indeed, lipid oxidation triggers chemical transformations that can alter lipid packing; change the membrane surface area, thickness and elastic modulus; and induce pore formation and phase separation. Here, we highlight how lipid hydroperoxides promote membrane remodelling and phase separation. Further, we emphasize the alterations caused by truncated oxidized lipids that lead to increased membrane permeability. Finally, the consequences of lipid photooxidation on cell functions are also discussed.

Numerical Studies of Shape Recovery of a Red Blood Cell Using Dissipative Particle Dynamics

A biological cell exhibits viscoelastic behavior mainly because its components (membrane and cytoplasm) are viscoelastic, and this is clearly seen when it is stretched and released. The present work numerically studied the shape recovery of a red blood cell (RBC) based on a viscoelastic model at the meso-scale using Dissipative Particle Dynamics (DPD) method. In this model, the RBC membrane is represented by a triangular network of worm-like chains, while the cytoplasm is replaced by a system of DPD particles. This viscoelastic model is validated by examining the stretching deformation of an RBC and comparing with the existing experimental data. Viscoelastic properties of the RBC are then analyzed by stretching an RBC under a 20 pN stretching force, and allowing it to relax. The time to recover its shape upon removal of the stretching force is measured to be 111 and 92.6[Formula: see text]ms for an RBC with and without cytoplasm, and the corresponding membrane viscosity is [Formula: see text] and [Formula: see text] [Formula: see text], respectively. These values, for an RBC with cytoplasm, are closer to experimental data than those for an RBC without cytoplasm, lending support to the model with cytoplasm. Finally, parametric studies are conducted on the membrane elastic and bending moduli. The results show that the shape recovery time decreases with increasing the membrane elastic and bending moduli.

A local instantaneous surface method for extracting membrane elastic moduli from simulation: Comparison with other strategies

Advances over the past decade have made it possible to extract elastic constants of lipid assemblies from molecular dynamics simulations. We summarize existing strategies for obtaining membrane elastic moduli and clarify the differences in the underlying approaches. We analyze these strategies in depth, including several important advantages and limitations. By addressing these limitations, we obtain a newly formulated spatially local methodology for extracting bending and tilt moduli: The Real Space Instantaneous Surface Method (ReSIS). With its freely available implementation, this method is designed for highly dynamic systems with arbitrary interface geometries. We demonstrate how the method provides consistent results for membranes of arbitrary size. In addition, we describe alternative implementations of various Fourier-space methods, and use these to compare the results from the different available methods and from published computational data. We specifically focus on the tilt modulus, where very large differences between Fourier and real-space based methods are observed, including those derived using ReSIS. These discrepancies are likely due to the known difference between model moduli and thermodynamic moduli that are derived from the corresponding response functions. In addition, we reexamine the issue of angular degeneracy and its effect on conformational ensembles. Finally, a van ’t Hoff analysis of the tilt and bending moduli reveals that both modes act as entropic springs and that enthalpy favors nonzero tilt, perhaps heralding the spontaneous lipid chain tilt of the gel phase at lower temperatures.

Receptor-mediated endocytosis generates nanomechanical force reflective of ligand identity and cellular property.

Whether environmental (thermal, chemical, and nutrient) signals generate quantifiable, nanoscale, mechanophysical changes in the cellular plasma membrane has not been well elucidated. Assessment of such mechanophysical properties of plasma membrane may shed lights on fundamental cellular process. Atomic force microscopic (AFM) measurement of the mechanical properties of live cells was hampered by the difficulty in accounting for the effects of the cantilever motion and the associated hydrodynamic force on the mechanical measurement. These challenges have been addressed in our recently developed control-based AFM nanomechanical measurement protocol, which enables a fast, noninvasive, broadband measurement of the real-time changes in plasma membrane elasticity in live cells. Here we show using this newly developed AFM platform that the plasma membrane of live mammalian cells exhibits a constant and quantifiable nanomechanical property, the membrane elasticity. This mechanical property sensitively changes in response to environmental factors, such as the thermal, chemical, and growth factor stimuli. We demonstrate that different chemical inhibitors of endocytosis elicit distinct changes in plasma membrane elastic modulus reflecting their specific molecular actions on the lipid configuration or the endocytic machinery. Interestingly, two different growth factors, EGF and Wnt3a, elicited distinct elastic force profiles revealed by AFM at the plasma membrane during receptor-mediated endocytosis. By applying this platform to genetically modified cells, we uncovered a previously unknown contribution of Cdc42, a key component of the cellular trafficking network, to EGF-stimulated endocytosis at plasma membrane. Together, this nanomechanical AFM study establishes an important foundation that is expandable and adaptable for investigation of cellular membrane evolution in response to various key extracellular signals.

Biophysical Characterization of Lipid Membranes: Effect of Lipid Head Groups and Tails on Synthetic and Natural Lipid Membranes

Lipid membranes play important roles in cell biology. They serve as a structure that protects cellular organelles and maintains unique cell shapes and also as a regulator that controls cellular functions. Thus, understanding the biophysical characteristics lipid membranes, e.g., fluidity and elasticity, is essential, as membrane proteins in cells often modulate these characteristics to properly control cellular activities. Here, we investigate various lipid head groups and tails by utilizing three different experimental techniques: 1) fluorescence recovery after photobleaching (FRAP), 2) black lipid membrane (BLM) electrophysiology recordings, and 3) atomic force microscopy (AFM). Our results show lipid membranes composed of either negatively charged headgroups or lactocylated headgroups have slower lateral diffusion coefficients and reduced elasticity compared to lipids with neutrally charged headgroups or zwitterionic headgroups. Addition of methyl groups in the acyl chain of the lipids decreases lateral diffusion but does not change elasticity of the membrane. Further, we study the biophysical characteristics of two natural lipid membranes extracted from E. coli and P. furiosus, which have known lipid compositions are distinct from each other, and compare our findings from synthetic lipids to understand the biophysical characteristics of natural membranes. We observed that P. furiosus lipid membranes exhibit a slower lateral diffusion and less elasticity compared with E. coli lipid membranes. From correlation among lateral diffusion, gA lifetime (local bending energy), and elasticity, we found that lipid membranes with slower lateral diffusion shows bigger local bending energy and membrane elastic modulus.

Membrane Stiffening in Osmotic Swelling: Analysis of Membrane Tension and Elastic Modulus.

The effects of osmotic swelling on key cellular biomechanical properties are explored in this chapter. We present the governing equations and theoretical backgrounds of themodels employed to estimate cell membrane tension and elastic moduli from experimental methods, and provide a summary of the prevailing experimental approaches used to obtain these biomechanical parameters. A detailed analysis of the current evidence of the effects of osmotic swelling on membrane tension and elastic moduli is provided. Briefly, due to the buffering effect of unfolding membrane reservoirs, mild hypotonic swelling does not change membrane tension or the adhesion of the membrane to the underlying cytoskeleton. Conversely, osmotic swelling causes the cell membrane envelope to stiffen, measured as an increase in the membrane elastic modulus.

Introducing surface tension to spacetime

Concepts from physical chemistry of surfaces and surface tension are applied to spacetime. More specifically, spacetime is modeled as a spatial fluid continuum bound together by a multi-dimensional membrane of time. A metric tensor that relates empty flat spacetime to energetic curved spacetime is found. Equations of motion for an infinitesimal unit of spacetime are derived. The equation of motion in a time-like direction is a Klein-Gordon type equation. The equations of motion in space-like directions take the form of Schrodinger’s equation where Plank’s constant is related to membrane elastic modulus. Although much work remains, it is suggested that the spacetime surface tension may serve as a mechanical model for many phenomena in quantum mechanics and atomic particle physics.