Formation and diffusivity characterization of supported lipid bilayers with complex lipid compositions

The moving edge of a hydrodynamically manipulated supported lipid bilayer (SLB) can be used to catalyze SLB formation of adsorbed lipid vesicles that do not undergo spontaneous SLB formation upon adsorption on SiO(2). By removing the lipid reservoir of an initially formed SLB, we show how a hydrodynamically moved SLB patch composed of POPC can be used to form isolated SLBs with compositions that to at least 95% represent that of the adsorbed lipid vesicles. The concept is used to investigate the diffusivity of lissamine rhodamine B 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (rhodamine-DHPE) in SLBs made from complex lipid compositions, revealing a decrease in diffusivity by a factor of 2 when the cholesterol content was increased from 0% to 50%. We also demonstrate how the concept can be used to induce stationary domains in SLBs containing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and cholesterol (39:21:40 mol %, respectively). Because the method serves as a means to form SLBs with lipid compositions that hamper SLB formation via spontaneous rupture of adsorbed lipid vesicles, it opens up the possibility for new biophysical investigations of SLBs with more nativelike compositions.     

Scanning force microscopy based rapid force curve acquisition on supported lipid bilayers: experiments and simulations using pulsed force mode.

In situ pulsed force mode scanning force microscopy (PFM-SFM) images of phase separated solid-supported lipid bilayers are discussed with the help of computer simulations. Simultaneous imaging of material properties and topography in a liquid environment by means of PFM-SFM is severely hampered by hydrodynamic damping of the cantilever. Stiffness and adhesion images of solid-supported membranes consisting of cholesterol, sphingomyelin, and 1,2-dioleyl-phosphatidylcholine obtained in aqueous solution exhibit contrast inversion of adhesion and stiff. ness images depending on parameters such as driving frequency, amplitude, and trigger setting. Simulations using a simple harmonic oscillator model explain experimental findings and give a deeper insight into the way PFM-SFM experiments have to be performed in order to obtain interpretable results and hence pave the way for reliable material contrast imaging at high speed.     

PAMAM dendrimer interactions with supported lipid bilayers: a kinetic and mechanistic investigation

The interaction kinetics of polyamidoamine (PAMAM) dendrimers with supported lipid bilayers of 1,2-sn-glycero-dimyristoylphosphocholine prepared by the vesicle deposition has been probed by optical waveguide lightmode spectroscopy and atomic force microscopy (AFM). In particular, the influence of PAMAM dendrimer generation (G2, G4, and G6) and concentration (1 to 100 nM) on the levels of adsorption and lipid bilayer removal have been determined as a function of time; hence interaction kinetics and mechanisms have been further elucidated. Dendrimer interaction kinetics with the lipid bilayer are concentration dependent in a complex manner, with net bilayer removal at 1 and 100 nM and net adsorption at 10 nM; these effects are irrespective of dendrimer generation. The pseudo first order rate constant for bilayer removal (at 1 and 100 nM) follows the order G6 > G4 > G2. In contrast, the pseudo first order rate constant for adsorption at 10 nM follows the order G2 > G4 > G6. AFM has confirmed expansion of lipid bilayer defects, hole formation, and adsorption to the bilayer or bilayer defects, and their concentration and generation dependence. These findings have implications when designing dendrimers for specific biopharmaceutical activities, e.g., as drugs, drug delivery vehicles, transfection agents, or antimicrobials.     

聚乙烯醇/丝胶共混凝胶薄膜的制备与表征

采用反复冷冻-解冻的方法制备了聚乙烯醇/丝胶共混凝胶薄膜,考察了薄膜热性能、力学性能和在水中的失重率,并对其微观结构进行了分析。结果表明:当制备过程中循环冷冻-解冻次数增加,且共混薄膜中丝胶与聚乙烯醇的含量相等时,可提高薄膜的综合性能。     

Poly(dimethylsiloxane)-coated sensor devices for the formation of supported lipid bilayers and the subsequent study of membrane interactions

The development of smooth hydrophilic surfaces that act as substrates for supported lipid bilayers (SLBs) is important for membrane studies in biology and biotechnology. In this article, it is shown that thin films of poly(dimethylsiloxane) (PDMS) formed on a sensor surface can be used as a substrate for the deposition of reproducible and homogeneous zwitterionic SLBs by the direct fusion of vesicles. Poly(dimethylsiloxane) solution (1% w/v) was spin coated on Love acoustic wave and surface plasmon resonance devices to form a thin PDMS layer. Acoustic, fluorescence, and contact angle measurements were used for the optimization of the PDMS film properties as a function of plasma etching time; parameters of interest involve the thickness and hydrophilicity of the film and the ability to induce the formation of homogeneous SLBs without adsorbed vesicles. The application of PDMS-coated sensor devices to the study membrane of interactions was demonstrated during the acoustic and fluorescence detection of the binding of melittin and defensin Crp4 peptides to model supported lipid bilayers.     

Gallic Acid-Loaded Sodium Alginate-Based (Polyvinyl Alcohol-Co-Acrylic Acid) Hydrogel Membranes for Cutaneous Wound Healing: Synthesis and Characterization

Traditional wound dressings often cannot treat wounds caused by bacterial infections or other wound types that are insensitive to these wound treatments. Therefore, a biodegradable, bioactive hydrogel wound dressing could be an effective alternative option. The purpose of this study was to develop a hydrogel membrane comprised of sodium alginate, polyvinyl alcohol, acrylic acid, and gallic acid for treating skin wounds. The newly developed membranes were analyzed using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), sol-gel fraction, porosity, mechanical strength, swelling, drug release and data modelling, polymeric network parameters, biodegradation, and antioxidation (DPPH and ABTS) and antimicrobial activity against Gram-positive and negative bacteria. The results revealed that hydrogel membranes were crosslinked successfully and had excellent thermal stability, high drug loading, greater mechanical strength, and exhibited excellent biodegradation. Additionally, the swelling ability and the porosity of the surface facilitated a controlled release of the encapsulated drug (gallic acid), with 70.34% release observed at pH 1.2, 70.10% at pH 5.5 (normal skin pH), and 86.24% at pH 7.4 (wounds pH) in 48 h. The gallic acid-loaded hydrogel membranes showed a greater area of inhibition against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli bacteria as well as demonstrated excellent antioxidant properties. Based on Franz cell analyses, the permeation flux of the drug from optimized formulations through mice skin was 92 (pH 5.5) and 110 (pH 7.4) μg/cm²·h⁻¹. Moreover, hydrogel membranes retained significant amounts of drug in the skin for 24 h, such as 2371 (pH 5.5) and 3300 µg/cm² (pH 7.4). Acute dermal irritation tests in rats showed that hydrogel membranes were nonirritating. Hydrogel membranes containing gallic acid could be an effective option for improving wound healing and could result in faster wound healing.     

Recent progress in the application of atomic force microscopy for supported lipid bilayers

In the past two decades, atomic force microscopy has been widely used for studying supported lipid bilayer related research, including the structure and dynamics of membranes and membrane proteins, and the interaction of membranes with chemical and biological molecules. The focus of this minireview is on the recent progress in the application of atomic force microscopy for supported lipid bilayers. Such progress mainly includes the application in the following aspects: submolecular-resolution imaging, in situ observation, and nanomechanics measurement.     

Synthesis of nitrilotriacetic acid terminated tethers for the binding of His-tagged proteins to lipid bilayers and to gold

Nitrilotriacetic acid terminated tethers for trapping of His-tagged proteins have been synthesized and characterized. Compound 1, containing a lipophilic cholesterol anchor, hydrophilic oligoethoxy chain linker, and nitrilotriacetic acid terminus, can be used for attaching His-tagged proteins to phospholipid bilayers. Compound 2, containing a gold binding thioacetate anchor, hydrophilic oligoethoxy chain, and nitrilotriacetic acid terminus, can be used to tether His-tagged proteins to a gold surface.     

Effect of acidity on the formation of solvent-free lipid bilayers

Glasses with hydrophobized surface are used to form “dry” bilayer lipid membranes (BLM). The contact angle on the silaned glass plates reaches 125°. Partitions of this kind, as opposed to polymer films, make a system more resistant to heat oscillations and mechanical perturbations generated when studying membranes properties. The specific capacitance of BLM (0.86 ± 0.04 μF cm^?2) testifies to the solvent absence in the bilayer. The dramatic drop of the capacitance (area) of the dry membranes with increasing pH is caused by a greater adsorption of lipid molecules on the hydrophobic substrate, which is probably due to changing conformation of their polar “head.”     

Cyclic voltammetry study of glucose and insulin interactions with supported lipid membrane

The effect of D-glucose and insulin on conducting properties of supported bilayer lipid membranes (s-BLM) modified by anthraquinone-2-sulphonic acid (AQS) at the presence of potassium ferricyanide was studied by means of cyclic voltammetry (CV). Both the oxidation and the reduction current peaks were found to decrease at the presence of glucose in concentration range varying from 10 to 320 mM. The influence of insulin on membrane properties is ambiguous. While the pretreatment of membrane with 20 mU l(-1) of insulin evoked slight increase of the current with unchanged course of the dependence of peak current on glucose, the decrease of conductance was observed above 10(5) mU l(-1) of insulin.     

Effects of surface pressure and internal friction on the dynamics of shear-driven supported lipid bilayers

Supported lipid bilayers (SLBs) are one of the most common model systems for cell membrane studies. We have previously found that when applying a bulk flow of liquid above an SLB the lipid bilayer and its constituents move in the direction of the bulk flow in a rolling type of motion, with the lower monolayer being essentially stationary. In this study, a theoretical platform is developed to model the dynamic behavior of a shear-driven SLB. In most regions of the moving SLB, the dynamics of the lipid bilayer is well explained by a balance between the hydrodynamic shear force arising from the bulk flow above the lipid bilayer and the friction between the upper and lower monolayers of the SLB. These two forces result in a drift velocity profile for the lipids in the upper monolayer of the SLB that is highest at the center of the channel and decreases to almost zero at the corners of the channel. However, near the front of an advancing SLB a very different flow behavior is observed, showing an almost constant drift velocity of the lipids over the entire bilayer front. In this region, the motion of the SLB is significantly influenced by gradients in the surface pressure as well as internal friction due to molecules that have accumulated at the front of the SLB. It is shown that even a modest surface fraction of accumulated molecules (～1%) can drastically affect the behavior of the SLB near the bilayer front, forcing the advancing lipids in the SLB away from the center of the channel out toward the sides.     

Photoelectric measurements of self-assembled and supported planar lipid bilayers: a new technique for studying apoptosis

A new method based on photoelectrochemistry for analyzing apoptosis of bilayer lipid membranes (s-BLMs) containing MCF-7 nuclei is reported. The s-BLM cell responded to white light (200–800 nm). During the apoptosis induced by Taxol, the photoelectric current of the cell decreased, suggesting degradation of the nuclear DNA. Electron transfer along the DNA double helix and along the nuclear skeleton is assumed in the interpretation. This novel photoelectric analytical method may provide a rapid and sensitive technique to evaluate apoptosis.     

Electron microscopic and chemisorption studies of the dispersity of supported rhodium catalysts of various compositions

The dispersity and size distribution of metal particles in mono- and bimetallic rhodiumcontaining catalysts prepared via decomposition of SiO₂- and Al₂O₃-supported complexes and impregnation of the support by inorganic metal compounds have been studied.

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, SiO₂ Al₂O₃ .

     

Agar-supported lipid bilayers — basic structures for biosensor design. Electrical and mechanical properties

The lipid bilayer is widely accepted as the basic structure of all biological membranes. Known as BLM (bilayer lipid membrane), it can be prepared artificially. Suitably modified, the BLM serves as a very appropriate model for biological membranes. Recent investigations have verified the high analytical potential of artificial lipid membranes. With a structure and composition almost identical to the lipid moiety of biomembranes, the BLM may serve as an ideal host for receptor molecules of biological origin, thus becoming a transducer which could “see” the environment the way the living cell does. For the construction of lipid bilayer based biosensors; however, stable, easy to prepare and long-lasting lipid membranes are required. With this aim in mind, we have prepared lipid bilayer membranes which use an agar gel as support. This as-BLM (agar-supported BLM) has been shown to possess the same electrical, mechanical and dynamic properties the conventional BLM is famous for, along with the benefits of long-term stability and considerably elevated breakdown voltages. Its preparation on the tip of an agar-filled Teflon tube of 0.5 mm diameter is easy and can be performed even by less-skilled personnel.

In an attempt of further miniaturization the concept of the as-BLM was applied to thin-film micro-systems manufactured by standard micro-electronic techniques. The result is a lipid bilayer system, which, while preserving all the essential properties of the bilayer lipid membrane, can serve as a basic building block for cheap, disposable biosensoric systems.     

Amphiphilic peptides as models for protein-membrane interactions: interfacial behaviour of sequential Lys- and Leu-based peptides and their penetration into lipid monolayers

Synthetic peptides constructed with doublets of hydrophobic residues tandemly repeated with doublets of positively charged residues, (Leu-Lys-Lys-Leu)_n, were used as models for the study of protein-membrane interactions. Their behaviour has been compared with that of their strictly alternating iso peptides, (Leu-Lys)_n. Both peptides present a random coil structure in pure water. In saline solutions, (Leu-Lys-Lys-Leu)_n peptides adopt an α-helical structure whereas (Leu-Lys)_n transit into a β-sheet structure. These peptides form multilayer assemblies on a pure water subphase but they are organized in monomolecular films on a saline aqueous subphase. The stability of these films increases with the peptide length. Structured peptides (α helices and β sheets) penetrate readily into lipid monolayers, whereas the penetration of unordered peptides is very slow. We have not observed any significant difference between the behaviour of a helices and β-sheet structures.     

Atomic force microscope studies on the interactions of Candida rugosa lipase and supported lipidic bilayers

Using the Langmuir–Blodgett technique we prepared substrate supported well-defined lipid/phospholipid (1-mono-palmitoyl-rac-glycerol (MPG)/l,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC)) bilayers in which the MPG lipid leaflet was exposed to the aqueous phase. Hydrolysis of MPG performed by Candida rugosa lipase (CRL) on the upper MPG layer of these supported bilayers on mica was imaged by real time atomic force microscope (AFM) using a liquid cell, so that the area increase of the initial structural defects could be followed over time. Our data strongly suggest that the edges of the initial structural defects are the preferred activation sites for CRL once the enzyme is adsorbed onto these interfaces. When a 2.5 nM bulk concentration of CRL was assayed on this planar lipid substrate, we found a long lag phase before a sharp increase of catalytic activity. The lag–burst kinetic behaviour was related to the interfacial activation phenomenon although we propose that it is also dependent on the gel-phase state of this interface.     

Amphiphilic Nanoparticles Control the Growth and Stability of Lipid Bilayers with Open Edges

Molecular amphiphiles self‐assemble in polar media to form ordered structures such as micelles and vesicles essential to a broad range of industrial and biological processes. Some of these architectures such as bilayer sheets, helical ribbons, and hollow tubules are potentially useful but inherently unstable owing to the presence of open edges that expose the hydrophobic bilayer core. Here, we describe a strategy to stabilize open bilayer structures using amphiphilic nanoparticle surfactants that present mixtures of hydrophilic and hydrophobic ligands on their surface. We observe that these particles bind selectively to the open edge of bilayer membranes to stabilize otherwise transient amphiphile assemblies. We show how such particles can precisely control the size of lipid tubules, how they can inhibit the formation of undesirable assemblies such as gallstone precursors, and how they can stabilize free‐floating lipid microdiscs.     

白光发射超分子水凝胶的构筑和发光性能研究

具有白光发射性质且发光可调的超分子水凝胶在发光材料和荧光检测领域具有广泛的应用前景.采用双（2-氨基丙基醚）聚丙二醇（PPG-NH²）链穿线带有正电荷的6-乙二胺修饰β-环糊精构成准轮烷,进而与锂皂石作用构筑了超分子水凝胶,并通过流变、zeta电势和扫描电镜等手段对凝胶性质进行了表征.当将扭曲分子内电荷转移（TICT）型的有机染料分子硫黄素T（ThT）和碘化4-[4-（二甲基氨基）苯乙烯基]-1-甲基吡啶鎓（DASPI）引入到水凝胶中,这两种有机染料能够在凝胶相中发生荧光共振能量转移（FRET）,从而产生包括白光在内的不同颜色的荧光发射.本研究为水基超分子发光软材料提供了一种新的构筑方法.     

A pH-Sensitive Hydrogel with Hydrophobic Association for Controlled Release of Poorly Water-Soluble Drugs

A novel pH-sensitive hydrogel has been developed by UV induced radical polymerization of acrylic acid (AA) and amphiphilic macromonomer polyethylene glycol monolaurylether monoacrylate (PEGLA) with crosslinker ethylene glycol dimethacrylate for controlled release of acyclovir, a poor water-soluble model drug. The swelling behavior was investigated in the buffer of different pH at I = 0.1 M, as well as in the ethanol/water mixture. The hydrophobic association formed by the hydrocarbon chains in PEGLA was found to dominate the swelling properties of the hydrogels with subordinate pH sensitivity due to the ionization of the AA segments. Therefore, the drug loading of acyclovir has been improved and the release rate of acyclovir was slowed down with increasing the PEGLA content in the hydrogels. By fitting the release data with Weibull equation, the acyclovir release kinetics was changed from the Fickian diffusion to an anomalous diffusion when the PEGLA content in the hydrogels was beyond 20 mol%.