Interaction of nanoparticles with lipid membrane

A nanoscale range of surface feature curvatures where lipid membranes lose integrity and form pores has been found experimentally. The pores were experimentally observed in the l-alpha-dimyristoyl phosphatidylcholine membrane around 1.2-22 nm polar nanoparticles deposited on mica surface. Lipid bilayer envelops or closely follows surface features with the curvatures outside of that region. This finding provides essential information for the understanding of nanoparticle-lipid membrane interaction, cytotoxicity, preparation of biomolecular templates and supported lipid membranes on rough and patterned surfaces.     

Curvature-driven membrane lipid and protein distribution

Cellular transport requires that membranes have the ability to recruit specific lipids and proteins to particular positions and at specific times. Here, we review recent work showing that lipids and proteins can be redistributed by spatially varying membrane curvature, without necessarily the need for biochemical targeting signals. We present here an emerging understanding of the various mechanisms by which membrane curvature can sort lipids and proteins, providing the experimental methods in addition to the supporting theoretical concepts.     

In-plane homogeneity and lipid dynamics in tethered bilayer lipid membranes (tBLMs)

Tethered bilayer lipid membranes (tBLMs) were prepared by the self-assembly of thiolated lipidic anchor molecules on gold, followed by phospholipid precipitation via rapid solvent exchange. They were characterized by their in-plane structure, dynamics and dielectric properties. We find that the in-plane homogeneity and resistivity of the tBLMs depend critically on a well-controlled sample environment during the rapid solvent-exchange procedure. The in-plane dynamics of the systems, assessed by fluorescence correlation spectroscopy (FCS) as the diffusivity of free, labeled phospholipid dissolved in the membrane, depend on the density of the lipidic anchors in the bilayer leaflet proximal to the substrate as well as on details of the molecular structure of the anchor lipid. In DOPC tBLMs in which tethers are laterally dilute (sparsely tethered bilayer lipid membranes, stBLMs), measured diffusivities, D ≈ 4 μm(2) s(-1), are only slightly greater than those reported in physisorbed bilayers (M. Przybylo, J. Sykora, J. Humpolíckova, A. Benda, A. Zan and M. Hof, Langmuir, 2006, 22, 9096-9099). However, when we distinguish label diffusion in the proximal and in the distal bilayer leaflets, we observe distinct diffusivities, D ≈ 2 μm(2) s(-1) and 7 μm(2) s(-1), respectively. The value observed in the distal leaflet is identical to that in free membranes. stBLMs completed with phytanoyl lipids (DPhyPC) show consistently lower label diffusivity than those completed with unsaturated chains (DOPC). As the length of the tether chain increases, a reduction in the apparent diffusivity is observed, which we interpret as an increased propensity of the proximal bilayer leaflet to host free lipid. We also investigated preparation conditions that control whether the tBLMs are laterally homogeneous, as assessed by optical microscopy. In laterally heterogeneous bilayers, the label diffusivity varies only by a factor of ~2 to 4, indicating that the regions in the bilayers with different label solubilities do not correspond to distinct phases, such as a fluid phase coexisting with a gel phase.     

微型支撑双层类脂膜pH电极的研制

把对氢质子敏感的四氯对位苯醌 (TCPBQ)置于在不锈钢丝末端的双层类脂膜 (s -BLM)里 .然后将这种固体支撑的s -BLM作为工作电极 ,Ag -AgCl电极作为参比电极 ,在各种pH水溶液里测得的电动势与pH的关系符合Nernst公式 .这种s -BLM电极易于制备 ,尺寸很小 (直径只有 0 .2mm) ,能在两天内保持稳定 .用这种电极对常规pH计难以测定的水包油型乳状液的pH作了测定 ,得到较好的结果 .     

Radial sizing of lipid nanotubes using membrane displacement analysis

We report a novel method for the measurement of lipid nanotube radii. Membrane translocation is monitored between two nanotube-connected vesicles, during the expansion of a receiving vesicle, by observing a photobleached region of the nanotube. We elucidate nanotube radii, extracted from SPE vesicles, enabling quantification of membrane composition and lamellarity. Variances of nanotube radii were measured, showing a growth of 40-56 nm, upon increasing cholesterol content from 0 to 20%.     

Comparison of the effect of lipid A analog E5531 and the lipid A from Escherichia coli on phospholipid membrane properties

The effect of the lipid A analog E5531 on the phospholipid membrane was compared with that of the lipid A from Escherichia coli (EC). E5531 decreased the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) membrane and increased the fluidity and micropolarity. On the other hand, the effect of EC on the membrane was contradictory. These results suggested that the reason for the difference of biological effects of these two lipid A would be caused by the differences from the effect on the cell membranes.     

Silicon-on-insulator based nanopore cavity arrays for lipid membrane investigation

We present the fabrication and characterization of nanopore microcavities for the investigation of transport processes in suspended lipid membranes. The cavities are situated below the surface of silicon-on-insulator (SOI) substrates. Single cavities and large area arrays were prepared using high resolution electron-beam lithography in combination with reactive ion etching (RIE) and wet chemical sacrificial underetching. The locally separated compartments have a circular shape and allow the enclosure of picoliter volume aqueous solutions. They are sealed at their top by a 250?nm thin Si membrane featuring pores with diameters from 2?μm down to 220?nm. The Si surface exhibits excellent smoothness and homogeneity as verified by AFM analysis. As biophysical test system we deposited lipid membranes by vesicle fusion, and demonstrated their fluid-like properties by fluorescence recovery after photobleaching. As clearly indicated by AFM measurements in aqueous buffer solution, intact lipid membranes successfully spanned the pores. The nanopore cavity arrays have potential applications in diagnostics and pharmaceutical research on transmembrane proteins.     

Non-Brownian diffusion of membrane molecules in nanopatterned supported lipid bilayers

Molecules associated with the outer surface of living cells exhibit complex, non-Brownian patterns of diffusion. In this report, supported lipid bilayers were patterned with nanoscale barriers to capture key aspects of this anomalous diffusion in a controllable format. First, long-range diffusion coefficients of membrane-associated molecules were significantly reduced by the presence of the barriers, while short-range diffusion was unaffected. Second, this modulation was more pronounced for large molecular complexes than for individual lipids. Surprisingly, the quantitative effect of these barriers on long-range lipid diffusion could be accurately simulated using a simple, continuum-based model of diffusion on a nanostructured surface; we thus describe a metamaterial that captures the properties of the outer membrane of living cells.     

A microfluidic vesicle screening platform: monitoring the lipid membrane permeability of tetracyclines

For many drugs including antibiotics such as tetracyclines it is crucial that the molecule has the ability to quickly and passively permeate lipid membranes. Hence, the understanding of the permeability in relation to the molecular structure is an important aspect to rationally design novel pharmaceutically active compounds with high bioavailability. Here, we present a versatile method to study the kinetics of tetracycline permeation across liposome membranes on a microchip. Liposomes are immobilized onto the glass surface in a stripe pattern via an avidin-biotin bond and covered by microchannels to allow continuous delivery of tetracycline and buffer. The fluid flow provides a constant concentration profile and thereby resembles the drug transport via blood in the human body. Total internal reflection fluorescence (TIRF) microscopy was used to image the formation of a fluorescent drug-europium complex inside the liposomes. The permeation rates of various tetracyclines were investigated and the results compared to a conventional method (water-octanol partitioning). The findings largely confirm the correlation between membrane permeability and lipophilicity of the permeating molecules (Overton's rule). However, slight deviations reveal that lipophilicity is an important but not the exclusive parameter for the prediction of permeation. The method is fast enough to study the permeation of unstable tetracyclines such as rolitetracycline. Additionally, with the use of different cholesterol concentrations, the influence of membrane composition on the permeation rate can be investigated conveniently. The microfluidic approach can be easily applied to investigate the kinetics of other processes such as ligand-membrane receptor association and dissociation, provided that the process can be visualized by means of fluorescence spectroscopy.     

Biotinylated lipid membrane patterns supported by proteins for the recognition of streptavidined polystyrene microspheres

Human serum albumin (HSA) patterns constructed on glass substrate by the micro-contact printing (microCP) technique are fabricated to support phospholipids membranes functionalized with biotinylated lipid. The experiment results indicate that this kind of lipid membrane has been assembled on HSA patterns with good stability. And the streptavidin-coated PS microspheres can be deposited on such lipid patterns with high efficiency. In this way, it may create a route to change the biological interface in the fabrication of biosensor.     

The effect of the membrane fluidity on pharmacokinetics for lipid A analog E5531

The effect of the dispersing procedure on the aggregate size, membrane fluidity and the pharmacokinetics were evaluated for the lipid A analog E5531. The size of the aggregates prepared by the pH-jump method (pH 11.0 → 7.3) was decreased, reaching 20 nm with increasing dispersing time in 0.003 N NaOH (pH 11.0). The membrane fluidity of the aggregates increased with increasing dispersing time. When prepared by the normal dilution method (pH 7.3 → 7.3), the size of the aggregates remained constant at 150 nm and the membrane fluidity was smaller compared to samples prepared by the pH-jump method. Using samples with different degrees of hydration and different membrane fluidities prepared by the pH-jump method, the pharmacokinetics after intravenous administration into rats were evaluated, and the data obtained confirmed that the membrane fluidity was correlated with the pharmacokinetics in rat. In addition, E5531 vials were stable for 24 months at room temperature when used within 24 hr after reconstitution.     

Wrinkle/slack model and finite element dynamics of membrane

This paper reviews conventional wrinkle models for anisotropic membrane and shows the relation between the models. A new wrinkle model is proposed which assumes virtual shear as well as virtual elongation of the membrane to estimate the real strain in the wrinkled region. This model coincides with the other models if the virtual shear and elongation is determined so that the strain energy is minimized. Another wrinkle/slack model is proposed for the dynamic analysis of thin isotropic membrane undergoing large overall motion with wrinkle and slack. It can take into account the residual compressive stress in the wrinkled and slack regions, i.e. the stiffness in the post‐buckling state. It is shown that the proposed model is a generalization of the conventional ones. Finite element formulation of the proposed model is described. Furthermore, the energy momentum conservation framework is constructed for the proposed membrane element, which achieves the unconditionally stable time integration. The total of the proposed method enables us to compute the overall motion of thin isotropic membrane such as the deployment of folded membrane, which has been one of the most difficult problems in aerospace engineering. Copyright © 2005 John Wiley & Sons, Ltd.     

计算流体力学在纳滤膜分离技术研究中应用

介绍了计算流体力学(CFD)在膜分离过程模拟中的基本原理,探讨了CFD在膜隔网优化设计、纳滤膜污染机理研究、纳滤膜对无机离子截留等领域中的应用,并对CFD在纳滤膜分离技术研究中的应用前景进行了展望.     

计算流体力学在膜技术及膜生物反应器研究中的应用

介绍了计算流体力学(CFD)的基本原理、内容和特点,综述了CFD在膜技术领域中的研究和发展,特别讨论了其在膜生物反应器(MBR)技术中的研究和应用,并对其应用前景进行了展望.     

平面薄膜结构耦合动力学特性研究与无量纲分析EI北大核心CSCD

利用固定界面的模态综合法建立了平面薄膜结构耦合动力学模型,精确得到了薄膜结构发生耦合振动的临界条件,分析了其耦合动力学特性。结果表明,与薄膜结构耦合基频有关的参数主要有薄膜预应力、框架弹性模量、截面惯性矩、长宽比、边长、框架横截面积、框架密度、薄膜密度和薄膜厚度。当薄膜预应力小于临界值时,薄膜结构的振动由薄膜来主导,当薄膜预应力大于临界值时,薄膜与框架发生耦合振动,此时薄膜结构的振动特性由薄膜与框架共同影响,并且随着薄膜预应力的增大,薄膜与框架发生耦合振动的阶数也随之增多并会出现振型顺序后移的现象。对薄膜结构的动力学特性进行了无量纲分析,推导了薄膜结构的小尺寸模型和大尺寸实物之间的相似准则。     

Fabrication of lipid tubules with embedded quantum dots by membrane tubulation protein

The first one-dimensional (1D) assembly of low-toxicity CuInS(2) /ZnS quantum dots (QDs) embedded in lipid nanotubules, formed from liposomes using the Amphiphysin-BAR (Bin-Amphiphysin-Rvs domain of human amphiphysin) protein to elongate the structure, is reported. The QD-containing lipid nanotubules display a high aspect ratio of ≈500:1 (≈40 nm diameter and 20 μm length) and are stable for more than 20 h. Furthermore, this methodology is extended to the assembly of various nanoparticle species within 1D lipid nanotubules, and includes materials such as CdSe and Au. Encapsulation within the hydrophobic core of the bilayer makes these materials highly biocompatible. The developed methodology and materials with these unique characteristics could be useful for various applications in nanobiotechnology and nanomedicine.     

Physicochemical and transport parameters for a lipid coated regenerated cellulose membrane

Physicochemical and NaCl characteristic transport parameters determined for a lipid coated regenerated cellulose membrane are reported. The lipid studied consists of glyceryl triestearate, while l-α-phosphatidylcholine and sodium taurocholate were used as surfactants. The RC-support and the lipid-modified membrane were characterized by X-ray photoelectron spectroscopy (XPS) at three different take off angles and X-ray diffraction. Transport parameters (salt diffusion and electrical resistance) were determined from salt permeation and impedance spectroscopy measurements performed with the membranes in contact with a NaCl constant concentration (C_c = 0.01 M). These results show a reduction in the transport parameters across the lipid coated membrane due to the lipid presence as well as its stability under mass and ion fluxes, which supports its application in liquid systems.     

Molecular dynamics study of dipalmitoylphosphatidylcholine lipid layer self-assembly onto a single-walled carbon nanotube

Single-walled carbon nanotubes (SWNTs) are possible nano-injectors and delivery vehicles of molecular probes and drugs into cells. In order to explore the interaction between lipid membranes and carbon nanotubes, we investigate the binding mechanism of dipalmitoylphosphatidylcholine (DPPC) with SWNTs by molecular dynamics. In low concentration range simulations, the DPPC molecules form a supramolecular two-layered cylindrical structure wrapped around the carbon nanotube surface. The hydrophobic part of DPPC is adsorbed on the surface of the nanotube, and the hydrophilic top is oriented towards the aqueous phase. For higher concentration ranges, the DPPC molecules are found to form a supramolecular multi-layered structure wrapped around the carbon nanotube surface. At the saturation point a membrane-like structure is self-assembled with a width of 41.4 Å, which is slightly larger than the width of a cell membrane. Our study sheds light on the existing conflicting simulation data on adsorption of single-chained phospholipids.