Bilayer Formation Research Articles

Preparation of RBPM-Ru based on FPSu and its characterization through image segmentation

A membrane technology is one of the basic categories of water purification technologies that are used to treat wide range of salinity water from brackish to sea water. Bipolar membrane (BPM) is a special type of catalytic ion exchange membrane (IEM) which involves water dissociation reaction in intermediate layer. Here monopolar and bipolar IEMs with Ru (water dissociation catalyst) as intermediate layer (IL) are prepared with resin and glass fiber reinforcements using functionalized polysulfone polymer (RBPM-Ru). The prepared RBPM-Ru was characterized using universal testing machine, thermo gravimetric analysis, contact angle and chemical stability through conductivity and water absorption studies. In addition the present study highlights the new method of characterizing RBPM-Ru especially through image segmentation technique as one of the prior characteristic technique before SEM analysis to confirm its bi-layer formation in a single membrane because of its advantages like no cost requirement and less time consumption method with the same quality of accuracy. The performance of RBPM-Ru in a two-compartment electrodialytic cell was evaluated using correlated parameters such as pH, concentration and conductivity studies in both compartments. By using current voltage graph (I-V) the importance of incorporating catalytic material in IL for enhancing BPM water dissociation reaction were identified. Finaly it can be concluded that RBPM-Ru was expected to have better process efficiency due to lower co-ion leakage capacity when compared with results of polystyrene–divinylbenzene (PSDVB) based BPM under similar experimental conditions.

099 Ichthyosis associated with sphingosine 1-phosphate lyase deficiency is due to aberrant calcium and sphingolipid regulation

Loss of function of Sphingosine-1-phosphate lyase (SGPL1) is associated with a multi-systemic disorder consisting of primary adrenal insufficiency and steroid-resistant nephrotic syndrome, with a third of patients manifesting ichthyosis. S1P lyase carries out the final degradative step in the sphingolipid pathway, irreversible cleavage of sphingosine-1-phosphate (S1P). Upstream accumulation of sphingolipid intermediates, such as ceramides and sphingosine, which are integral in the formation of the lamellar lipid bilayer, have been identified in multiple SGPL1 KO cell types.

Simulation of the incubation time for the formation of (FeB/Fe2B) bilayer on pure iron

Abstract In this work, a mathematical model was used in order to study the growth kinetics of (Fe2B/FeB) bilayer during bori-ding process basing on the second Fick’s law and mass balance equation. The run of the numerical simulation allowed calculating the incubation time (τ) of each boronized layer (Fe2B or FeB), and estimating the effect of this parameter on the growth of the boronized layer. The boride incubation time for forming the FeB or Fe2B layer on the pure iron substrate was incorporated into the present mathematical model. To simulate the value of the growth rate constant and the incubation time for the bilayer configuration, the experimental data available in the literature concerning the boronizing of pure iron were considered. Based on the experimental and simulation results, it was shown that the incubation time decreases with increasing temperature in the FeB and Fe2B phases. It was concluded from this study that the thickness of each boride layer depended on its growth rate constant and on another parameter kτ which was the rate constant of incubation time.The obtained results confirmed the validity of the present mathematical model and gave a good estimate of the incubation time during the formation of each boride layer as well as formulated the variation of this parameter with a mathematical equation. Furthermore, the comparison of experimental data with the simulated results of boronized layer thickness allowed to validate the present model.

Magnetic interactions and spin excitations in van der Waals ferromagnet

Using a combination of density functional theory (DFT) and spin-wave theory methods, we investigate the magnetic interactions and spin excitations in semiconducting VI3. Exchange parameters of monolayer, bilayer, and bulk forms are evaluated by mapping the magnetic energies of various spin configurations, calculated using DFT+U, onto the Heisenberg model. The intralayer couplings remain largely unchanged in three forms of VI3, while the interlayer couplings show stronger dependence on the dimensionality of the materials. We calculate the spin-wave spectra within a linear spin-wave theory and discuss how various exchange parameters affect the magnon bands. The magnon–magnon interaction is further incorporated, and the Curie temperature is estimated using a self-consistently renormalized spin-wave theory. To understand the roles of constituent atoms on magnetocrystalline anisotropy energy (MAE), we resolve MAE into sublattices and find that a strong negative V-I inter-sublattice contribution is responsible for the relatively small easy-axis MAE in VI3.

A Study of the Effects of Plasma Surface Treatment on Lipid Bilayers Self-Spreading on a Polydimethylsiloxane Substrate under Different Treatment Times.

Plasma-treated poly(dimethylsiloxane) (PDMS)-supported lipid bilayers are used as functional tools for studying cell membrane properties and as platforms for biotechnology applications. Self-spreading is a versatile method for forming lipid bilayers. However, few studies have focused on the effect of plasma treatment on self-spreading lipid bilayer formation. In this paper, we performed lipid bilayer self-spreading on a PDMS surface with different treatment times. Surface characterization of PDMS treated with different treatment times is evaluated by AFM and SEM, and the effects of plasma treatment of the PDMS surface on lipid bilayer self-spreading behavior is investigated by confocal microscopy. The front-edge velocity of lipid bilayers increases with the plasma treatment time. By theoretical analyses with the extended-DLVO modeling, we find that the most likely cause of the velocity change is the hydration repulsion energy between the PDMS surface and lipid bilayers. Moreover, the growth behavior of membrane lobes on the underlying self-spreading lipid bilayer was affected by topography changes in the PDMS surface resulting from plasma treatment. Our findings suggest that the growth of self-spreading lipid bilayers can be controlled by changing the plasma treatment time.

Silver Nanoneedle Probes Enable Sustained DC Current, Single-Channel Resistive Pulse Nanopore Sensing.

Resistive pulse sensing using ion channel proteins (biological nanopores) has been evolving as a single-molecule approach to detect small biomolecules owing to atomically precise pore size reproducibility, high signal-to-noise ratio, and molecular selectivity. The incorporation of biological nanopores in sensing platforms requires a stable lipid membrane that can be formed by a variety of methods such as the painting method and droplet-based techniques. However, these methods are limited by the fragility of the unsupported bilayer or the need for specific microdevices. Electrode-supported bilayers, in which a metal electrode is used as a support structure, have been recently developed using a fine gold nanoneedle. We previously described the utility of the gold nanoneedle-supported ion channel probe to detect small molecules with high spatial resolution; however, it exhibited a channel current decay over time, which affected the binding frequency of the target molecule to the protein pore as well. Here, we introduce a silver nanoneedle probe to support the lipid bilayer formation and ion channel measurements. The silver nanoneedle mitigates the current decay observed on gold electrodes and produces stable DC channel currents. Our findings propose the formation of a AgCl layer creating a nonpolarizable electrode. The new nanoneedle is successfully applied for single-molecule detection of sulfonated β-cyclodextrin (S7βCD) using αHL as a test bed protein. We believe that this new silver nanoneedle platform has great potential given the relative ease of lipid bilayer formation and stable open channel currents.

Investigation of mechanical and tribological properties of electroless Ni-P-B ternary coatings on steel

The Ni–P-B ternary coating was prepared on steel specimens through electroless deposition and their microstructural and tribo-mechanical properties were investigated. Heat treatment of the as plated coating was carried out at 390 °C to realize its effect on microstructural, mechanical, tribological properties of the coating. Microstructural analysis was carried out to study phase structure, morphology, topography, and coating compositions by using XRD, FESEM, AFM, and EDS. Contact angle measurement was also performed to evaluate the wetting behavior of the coatings. The as-plated coating exhibited hydrophobic character with a contact angle of ∼ 96.7°, whereas the heat-treated coating resulted in hydrophilic character with a contact angle of ∼ 79.5°. Mechanical and tribological properties were evaluated by using Vickers microhardness, nanoindentation, and dry sliding friction test. It is observed that the heat treatment process has an excellent impact on mechanical and tribological properties. Heat-treated ternary coating resulted in higher hardness (6 GPa) than as-plated coating (5 GPa). Similarly, higher young’s modulus was also achieved in the heat-treated coating (232 GPa) during nanoindentation experiments. Profound improvement in tribological performance is executed in both coatings over steel specimens. Maximum up to ∼ 33% and ∼ 45% decrement in COF is observed for as-plated and heat-treated Ni-P-B ternary coatings respectively. Due to greater hardness in heat-treated samples, the formation of the protective bilayer is observed along wear tracks as harder third particles created a strong adhesive bond by plastic deformation. The non-uniformity of the protective layer in the as-plated coating leads to higher COF and wear depth compared to heat-treated coating. Residual third particles behaved as micro cutters for as-plated coating while rolling effect is observed in case of heat-treated ternary coating.

Effect of initial WC particle size on grain growth behavior and gradient structure formation of bilayer functionally graded cemented carbides

In this study, functionally graded WC-TiC-Co cemented carbides with a unique bilayer microstructure have been successfully synthesized by high pressure nitriding sintering. The effect of initial WC particle size on the final gradient microstructure has been investigated systematically. The results show that a face-centered-cubic (fcc) phase-riched surface layer and an intermediate layer (cobalt-rich and coarse- WC grain) are formed during the nitriding sintering. With the increasing of initial WC particle size, the carbide grain size of the surface layer, the intermediate layer, and the inner region increases after sintering. Compared with the inner region, the intermediate layer shows significantly coarser WC grains. The thickness of the bilayer increases with the increment of initial WC particle size, which indicates that there is a constraining effect of ultrafine WC grains on the gradient microstructure formation. The formation mechanism of the bilayer functionally graded cemented carbides containing WC powder with different particle sizes is investigated by analyzing the diffusion path of Ti, N, Co and W, phase composition and grain growth during nitriding sintering.

2D Layered Dipeptide Crystals for Piezoelectric Applications

Abstract2D piezoelectric materials such as transition metal dichalcogenides are attracting significant attention because they offer various benefits over bulk piezoelectrics. In this work, the fabrication of layered biomolecular crystals of diphenylalanine (FF) obtained via a co‐assembly of l,l‐ and d,d‐ enantiomers of FF monomers is reported. Their crystal structure, thermal and chemical stabilities, and piezoelectric properties are investigated. Single crystal X‐ray diffraction results show that FF enantiomers are arranged in the form of bilayers consisting of monomers with alternating chirality packed into a tape‐like monoclinic structure belonging to a polar space group P21. Each bilayer (≈1.5 nm thick) demonstrates strong out‐of‐plane piezoelectricity (d33 ≈ 20 pm V−1) that is almost an order of magnitude higher than in the archetypical piezoelectric material quartz. The grown crystals demonstrate better thermal and chemical stabilities than self‐assembled hexagonal FF nanotubes studied in the past. Piezoelectric bilayers, being held via weak aromatic interaction in the bulk crystals, can be exfoliated by mechanical or chemical methods, thus resulting in a 2D piezoelectric material, which can find various applications in biocompatible and ecologically friendly electromechanical microdevices, such as sensors, actuators, and energy harvesting elements used in implantable and wearable electronics.

Structural Organization of Cardiolipin-Containing Vesicles as Models of the Bacterial Cytoplasmic Membrane.

The bacterial cytoplasmic membrane is the innermost bacterial membrane and is mainly composed of three different phospholipid species, i.e., phosphoethanolamine (PE), phosphoglycerol (PG), and cardiolipin (CL). In particular, PG and CL are responsible for the negative charge of the membrane and are often the targets of cationic antimicrobial agents. The growing resistance of bacteria toward the available antibiotics requires the development of new and more efficient antibacterial drugs. In this context, studying the physicochemical properties of the bacterial cytoplasmic membrane is pivotal for understanding drug-membrane interactions at the molecular level as well as for designing drug-testing platforms. Here, we discuss the preparation and characterization of PE/PG/CL vesicle suspensions, which contain all of the main lipid components of the bacterial cytoplasmic membrane. The vesicle suspensions were characterized by means of small-angle neutron scattering, dynamic light scattering, and electron paramagnetic spectroscopy. By combining solution scattering and spectroscopy techniques, we propose a detailed description of the impact of different CL concentrations on the structure and dynamics of the PE/PG bilayer. CL induces the formation of thicker bilayers, which exhibit higher curvature and are overall more fluid. The experimental results contribute to shed light on the structure and dynamics of relevant model systems of the bacterial cytoplasmic membrane.

The Transition From MoS2 Single-Layer to Bilayer Growth on the Au(111) Surface

The transition from single-layer to bilayer growth of molybdenum disulfide on the Au(111) surface is investigated by in situ low-energy electron and photoemission microscopy. By mapping the film morphology with nanometer resolution, we show that a MoS2 bilayer forms at the boundaries of single-layer single-domain MoS2 islands and next to merging islands whereas bilayer nucleation at the island centers is found to be suppressed, which may be related to the usage of dimethyl disulfide as sulfur precursor in the growth process. This approach, which may open up the possibility of growing continuous films over large areas while delaying bilayer formation, is likely transferable to other transition metal dichalcogenide model systems.

Robust Photoelectric Biomolecular Switch at a Microcavity-Supported Lipid Bilayer.

Biomolecular devices based on photo-responsive proteins have been widely proposed for medical, electrical, and energy storage and production applications. Also, bacteriorhodopsin (bR) has been extensively applied in such prospective devices as a robust photo addressable proton pump. As it is a membrane protein, in principle, it should function most efficiently when reconstituted into a fully fluid lipid bilayer, but in many model membranes, lateral fluidity of the membrane and protein is sacrificed for electrochemical addressability because of the need for an electroactive surface. Here, we reported a biomolecular photoactive device based on light-activated proton pump, bR, reconstituted into highly fluidic microcavity-supported lipid bilayers (MSLBs) on functionalized gold and polydimethylsiloxane cavity array substrates. The integrity of reconstituted bR at the MSLBs along with the lipid bilayer formation was evaluated by fluorescence lifetime correlation spectroscopy, yielding a protein lateral diffusion coefficient that was dependent on the bR concentration and consistent with the Saffman–Delbrück model. The photoelectrical properties of bR-MSLBs were evaluated from the photocurrent signal generated by bR under continuous and transient light illumination. The optimal conditions for a self-sustaining photoelectrical switch were determined in terms of protein concentration, pH, and light switch frequency of activation. Overall, a significant increase in the transient current was observed for lipid bilayers containing approximately 0.3 mol % bR with a measured photo-current of 250 nA/cm2. These results demonstrate that the platforms provide an appropriate lipid environment to support the proton pump, enabling its efficient operation. The bR-reconstituted MSLB model serves both as a platform to study the protein in a highly addressable biomimetic environment and as a demonstration of reconstitution of seven-helix receptors into MSLBs, opening the prospect of reconstitution of related membrane proteins including G-protein-coupled receptors on these versatile biomimetic substrates.

Structure, Nanomechanical Properties, and Wettability of Organized Erucamide Layers on a Polypropylene Surface.

Understanding the nanostructure and nanomechanical properties of surface layers of erucamide, in particular the molecular orientation of the outermost layer, is important to its widespread use as a slip additive in polymer materials. Extending our recent observations of nanomorphologies of erucamide layers on a hydrophilic silica substrate, here we evaluate its nanostructure on a more hydrophobic polypropylene surface. Atomic force microscopy (AFM) imaging revealed the molecular packing, thickness, and surface coverage of the erucamide layers, while peak force quantitative nanomechanical mapping (QNM) showed that erucamide reduced the adhesive response on polypropylene. Synchrotron X-ray reflectivity (XRR) was used to probe the out-of-plane structure of the surface layers. Static contact angle measurements further corroborated on the resulting wettability, also demonstrating the efficacy of erucamide physisorption in facilitating control over polypropylene surface wetting. The results show the formation of erucamide monolayers, bilayers and multilayers, depending on the concentration in the spin-cast solution. Correlation of AFM, XRR and wettability results consistently points to the molecular orientation in the outermost layer, i.e. with the erucamide tails pointing outward for the surface nanostructures with different morphologies (i.e., bilayers and multilayers). Rare occurrence of monolayers with exposed hydrophilic head groups were observed only at the lowest erucamide concentration. Compared with our previous observations on the hydrophilic surface, the erucamide surface coverage was much higher on the more hydrophobic propylene surface at similar erucamide concentrations in the spin-cast solution. Furthermore, the structure, molecular orientation and nanomechanical properties of the spin-cast erucamide multilayers atop polypropylene were also similar to those on industrially relevant polypropylene fibers coated with erucamide via blooming. These findings shed light on the nanostructural features of the erucamide surface layer underpinning its nanomechanical properties, relevant to many applications in which erucamide is commonly used as a slip additive.

Bio-Inspired Motion Mechanisms: Computational Design and Material Programming of Self-Adjusting 4D-Printed Wearable Systems.

This paper presents a material programming approach for designing 4D‐printed self‐shaping material systems based on biological role models. Plants have inspired numerous adaptive systems that move without using any operating energy; however, these systems are typically designed and fabricated in the form of simplified bilayers. This work introduces computational design methods for 4D‐printing bio‐inspired behaviors with compounded mechanisms. To emulate the anisotropic arrangement of motile plant structures, material systems are tailored at the mesoscale using extrusion‐based 3D‐printing. The methodology is demonstrated by transferring the principle of force generation by a twining plant (Dioscorea bulbifera) to the application of a self‐tightening splint. Through the tensioning of its stem helix, D. bulbifera exhibits a squeezing force on its support to provide stability against gravity. The functional strategies of D. bulbifera are abstracted and translated to customized 4D‐printed material systems. The squeezing forces of these bio‐inspired motion mechanisms are then evaluated. Finally, the function of self‐tightening is prototyped in a wrist‐forearm splint—a common orthotic device for alignment. The presented approach enables the transfer of novel and expanded biomimetic design strategies to 4D‐printed motion mechanisms, further opening the design space to new types of adaptive creations for wearable assistive technologies and beyond.

Adhesion Process of Biomimetic Myelin Membranes Triggered by Myelin Basic Protein.

The myelin sheath—a multi-double-bilayer membrane wrapped around axons—is an essential part of the nervous system which enables rapid signal conduction. Damage of this complex membrane system results in demyelinating diseases such as multiple sclerosis (MS). The process in which myelin is generated in vivo is called myelination. In our study, we investigated the adhesion process of large unilamellar vesicles with a supported membrane bilayer that was coated with myelin basic protein (MBP) using time-resolved neutron reflectometry. Our aim was to mimic and to study the myelination process of membrane systems having either a lipid-composition resembling that of native myelin or that of the standard animal model for experimental autoimmune encephalomyelitis (EAE) which represents MS-like conditions. We were able to measure the kinetics of the partial formation of a double bilayer in those systems and to characterize the scattering length density profiles of the initial and final states of the membrane. The kinetics could be modeled using a random sequential adsorption simulation. By using a free energy minimization method, we were able to calculate the shape of the adhered vesicles and to determine the adhesion energy per MBP. For the native membrane the resulting adhesion energy per MBP is larger than that of the EAE modified membrane type. Our observations might help in understanding myelination and especially remyelination—a process in which damaged myelin is repaired—which is a promising candidate for treatment of the still mostly incurable demyelinating diseases such as MS.

Formation of Supported Lipid Bilayers Derived from Vesicles of Various Compositional Complexity on Conducting Polymer/Silica Substrates.

Supported lipid bilayers (SLBs) serve important roles as minimalistic models of cellular membranes in multiple diagnostic and pharmaceutical applications as well as in the strive to gain fundamental insights about their complex biological function. To further expand the utility of SLBs, there is a need to go beyond simple lipid compositions to thereby better mimic the complexity of native cell membranes, while simultaneously retaining their compatibility with a versatile range of analytical platforms. To meet this demand, we have in this work explored SLB formation on PEDOT:PSS/silica nanoparticle composite films and mesoporous silica films, both capable of transporting ions to an underlying conducting PEDOT:PSS film. The SLB formation process was evaluated by using the quartz crystal microbalance with dissipation (QCM-D) monitoring, total internal reflection fluorescence (TIRF) microscopy, and fluorescence recovery after photobleaching (FRAP) for membranes made of pure synthetic lipids with or without the reconstituted membrane protein β-secretase 1 (BACE1) as well as cell-derived native lipid vesicles containing overexpressed BACE1. The mesoporous silica thin film was superior to the PEDOT:PSS/silica nanoparticle composite, providing successful formation of bilayers with high lateral mobility and low defect density even for the most complex native cell membranes.

Pharmacokinetic evaluation of the synergistic effect of raloxifene loaded transfersomes for transdermal delivery

The current research work involves the comparative evaluation of the synergistic potential of transfersomes with span 80, span 85 for transdermal delivery of raloxifene hydrochloride (RXN). The prepared transfersomes were optimised using size, entrapment efficiency, transdermal flux, and further characterised for other physicochemical properties. The fate of the drug within the lipid vesicles was investigated by differential scanning calorimetry and X-rays diffraction. Morphology, shape and 3-D structure was evaluated using electron microscopy. 31PNMR was carried out to evaluate the formation of lipid bilayers in the prepared vesicles. Vesicles size were found in the range of 90–140 nm with particle size and acceptable zeta potential. The transdermal flux of synergistic transfersomes (TSP-80 + 85) was much higher when compared with individual span 80 and span 85 based transfersome formulations. On the comparative evaluation of bioavailability in a rat model with transfersomal gel, oral tablet solution and hydroethanolic gel of active drug revealed that TSP-80 + 85-5 had a significant enhancement in the transdermal bioavailability in contrast to the other formulations. The study provided new insight into synergistic use of surfactants for transfersomes with successful transdermal delivery and bioavailability enhancement of poorly soluble and high metabolic rate drugs like raloxifene hydrochloride.

Temperature-Controlled Assembly and Characterization of a Droplet Interface Bilayer

This protocol details the use of a feedback temperature-controlled heating system to promote lipid monolayer assembly and droplet interface bilayer formation for lipids with elevated melting temperatures, and capacitance measurements to characterize temperature-driven changes in the membrane.

Temperature-Controlled Assembly and Characterization of a Droplet Interface Bilayer.

The droplet interface bilayer (DIB) method for assembling lipid bilayers (i.e., DIBs) between lipid-coated aqueous droplets in oil offers key benefits versus other methods: DIBs are stable and often long-lasting, bilayer area can be reversibly tuned, leaflet asymmetry is readily controlled via droplet compositions, and tissue-like networks of bilayers can be obtained by adjoining many droplets. Forming DIBs requires spontaneous assembly of lipids into high density lipid monolayers at the surfaces of the droplets. While this occurs readily at room temperature for common synthetic lipids, a sufficient monolayer or stable bilayer fails to form at similar conditions for lipids with melting points above room temperature, including some cellular lipid extracts. This behavior has likely limited the compositions-and perhaps the biological relevance-of DIBs in model membrane studies. To address this problem, an experimental protocol is presented to carefully heat the oil reservoir hosting DIB droplets and characterize the effects of temperature on the lipid membrane. Specifically, this protocol shows how to use a thermally conductive aluminum fixture and resistive heating elements controlled by a feedback loop to prescribe elevated temperatures, which improves monolayer assembly and bilayer formation for a wider set of lipid types. Structural characteristics of the membrane, as well as the thermotropic phase transitions of the lipids comprising the bilayer, are quantified by measuring the changes in electrical capacitance of the DIB. Together, this procedure can aid in evaluating biophysical phenomena in model membranes over various temperatures, including determining an effective melting temperature (TM) for multi-component lipid mixtures. This capability will thus allow for closer replication of natural phase transitions in model membranes and encourage the formation and use of model membranes from a wider swath of membrane constituents, including those that better capture the heterogeneity of their cellular counterparts.

The Role of Relative Capacitances in Impedance Sensing with Organic Electrochemical Transistors

AbstractThe organic electrochemical transistor (OECT) has attracted interest for use in biosensor technology due to its ability to transduce ionic to electronic signals and operate in aqueous environments. While OECTs have been broadly applied for biosensing and impedance characterization of biological systems, there is still no consensus on the ideal geometries, relative capacitances, and operational conditions for specific sensing scenarios. Here it is shown that for impedance sensing with a capacitive layer on the gate, gate‐limited OECTs produce the largest sensor response. An equivalent circuit model is used to study frequency response with non‐permeable and ion‐permeable membranes added to the gate and found that the transistor configuration, with respect to gate and channel capacitances, able to produce the largest sensor signal is determined by the capacitance to be sensed as well as the membrane permeability. The findings are applied to design a gold gate OECT capable of detecting formation of a lipid bilayer on the gate. The results indicate that high transconductance OECTs typically considered attractive do not deliver the largest sensor signals when used for impedance sensing. Results are presented in settings similar to those used in practical experiments, thereby providing guidance on how to best design OECTs for impedance biosensing.