疏水化工艺在数字化超微量微注射中的应用

在生物医学和微化学分析领域, 基于玻璃微针的微注射系统由于玻璃基质的亲水性,在微注射过程中会出现渗流、回流的现象,影响注射效果,不利于微注射量的检测和控制.本文介绍的疏水化工艺通过将微喷嘴（微针）内外表面特定区域进行疏水化处理,对微流体进行数字化驱动和控制,可改善微流体流动特性,提高微注射效果,使液滴按一定规律以球形颗粒喷射,有助于微流量的精确检测和微喷射的精确量可控.     

A study on the interaction between ibuprofen and bilayer lipid membrane

Ibuprofen is a well-known nonsteroidal anti-inflammatory drug, which can interact with lipid membranes. In this paper, the interaction of ibuprofen with bilayer lipid membrane was studied by UV-vis spectroscopy, cyclic voltammetry and AC impedance spectroscopy. UV-vis spectroscopy data indicated directly that ibuprofen could interact with lipid vesicles. In electrochemical experiments, ibuprofen displayed a biphasic behavior on bilayer lipid membrane supported on a glassy carbon electrode. It could stabilize the lipid membrane in low concentration, while it induced defects formation, even removed off bilayer lipid membrane from the surface of the electrode with increasing concentration. The mechanism about the interaction between ibuprofen and supported bilayer lipid membrane was discussed.     

Dry adhesion of polythiophene nanotube arrays with drag‐induced direction dependence

Polythiophene (Pth) bilayer films each consists of a nanotube layer and a compact layer had been prepared by electrochemical polymerization and using anodic aluminum oxide (AAO) membranes as template. The films were treated by mechanical polishing and freeze drying to improve the degree of orientation of nanotubes and their surface smoothness. A treated Pth bilayer film can adhere strongly on glass with its nanotube surface by applying a dragging preload. The applied dragging preload caused the original vertically aligned Pth nanotube array to tilt opposite to the direction of preload, which induced a superstrong shear adhesion force of up to 144 ± 30 N cm^?2 for the film with a tube length of 26 μm as the film was dragged along the direction of preload. However, the shear adhesion force opposite to the direction of dragging preload was relatively low (44 ± 17 N cm^?2). The direction‐dependent force management of Pth bilayer films is quite similar to that gecko does, indicating the potential for developing advanced adhesive systems. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

锚定的磷脂双层膜的制备及其形貌结构

利用表面硅烷化方法对化学氧化的单晶硅表面进行修饰,成功地将抗生物素蛋白固定在表面上,并且用囊泡融合法成功得到了大面积、连续的磷脂双层膜。由于成功地在基底与磷脂膜间引入了5nm左右的水层,原子力显微镜观察表明这种锚定的磷脂双层膜(tethered bilayer lipid membrane, tBLM)表现出与磷脂支持膜不同的相形为。两种膜相形为的不同可以用磷脂分子与基底间相互作用的不同来解释。     

Lipid exchanges between dioctadecyldimethylammonium bromide monolayer and vesicles in the subphase

Studies on the interaction of lipid monolayer with bilayer structures, such as vesicles, are relatively scarce in the literature. In order to ascertain whether these structures interact for cationic dioctadecyldimethylammonium bromide (DODAB) monolayers at the aqueous surfaces of 0, 0.05, and 0.5 mmol L⁻¹ DODAB vesicle dispersions, differential scanning calorimetry (DSC) and surface film balance experiments were carried out. DSC results confirmed the presence of unilamellar vesicles in the subphase, while changes in the monolayer surface pressure–area per molecule (π–A) isotherm profile yielded by the presence of DODAB vesicle in the subphase revealed monolayer-vesicle interactions as a result of monomer exchanges between the monolayer and the vesicles with stronger effects at the higher vesicle concentration investigated.     

Gene expression within cell-sized lipid vesicles

Functional protein synthesis was observed in cell-sized lipid vesicles following encapsulation of a gene-expression system. Expression of rsGFP (red-shifted green fluorescent protein) within individual vesicles was observed by fluorescence microscopy. Interestingly, at the early stage of the reaction, the expression efficiency inside the vesicle was remarkably higher than that in the solution outside. The synthesized rsGFP in individual vesicles is safe from attack by proteinase K added to the external aqueous solution. Studies on cell-sized vesicles expressing protein should contribute to a fundamental understanding of certain aspects of living systems and will be useful for practical applications, such as the construction of microreactors.     

Potassium ion transport by gramicidin and valinomycin across a Ag(1 1 1)-supported tethered bilayer lipid membrane

A tethered bilayer lipid membrane (tBLM) was prepared by anchoring a thiolipid monolayer to a Ag(1 1 1) single crystal from a thiolipid solution in ethanol; a diphytanoylphosphatidylcholine monolayer was then self-assembled on top of the thiolipid monolayer from a lipid solution in hexane or ethanol. The thickness of the mixed thiolipid|lipid bilayer was estimated at 7.5 ± 0.5 nm by scratching holes in the tBLM with an AFM tip and determining their height profile and the frequency distribution of height. The effect of the incorporation of gramicidin A and valinomycin upon K⁺ ion transport across the tBLM was investigated by electrochemical impedance spectroscopy. The position of the inflection point of the sigmoidal curve of the in-phase component of the electrode admittance against potential allowed the determination of an approximate scale of the absolute potential difference across the whole Ag(1 1 1)|(aqueous solution) interface, on the basis of a model of the electrified interface.     

Thermal buckling of initially compressed single-walled carbon nanotubes by molecular dynamics simulation

Thermal buckling of initially compressed single-walled carbon nanotubes subjected to a uniform temperature rise is presented by using molecular dynamics simulations. Comprehensive numerical calculations are carried out for armchair and zigzag carbon nanotubes with various geometric dimensions. The results show that thermal buckling can occur beyond a critical value of temperature when the tube is initially compressed to a point prior to buckling. The critical buckling temperature increases as the compressive load ratio parameter decreases, and varies dramatically with nanotube helicity, radius and length. Owing to strong thermal oscillations of carbon atoms, a zigzag carbon nanotube with relatively small radius can buckle at a surprisingly lower temperature than the expected one.     

Formation of giant protein vesicles by a lipid cosolvent method

This paper describes a method to create giant protein vesicles (GPVs) of ≥10 μm by solvent-driven fusion of large vesicles (0.1-0.2 μm) with reconstituted membrane proteins. We found that formation of GPVs proceeded from rotational mixing of protein-reconstituted large unilamellar vesicles (LUVs) with a lipid-containing solvent phase. We made GPVs by using n-decane and squalene as solvents, and applied generalized polarization (GP) imaging to monitor the polarity around the protein transmembrane region of aquaporins labeled with the polarity-sensitive probe Badan. Specifically, we created GPVs of spinach SoPIP2;1 and E. coli AqpZ aquaporins. Our findings show that hydrophobic interactions within the bilayer of formed GPVs are influenced not only by the solvent partitioning propensity, but also by lipid composition and membrane protein isoform.     

Thin lipid membranes with aqueous interfaces: Apparatus designs and methods of study

Thin membranes can be formed in aqueous media from amphiphilic lipids, and will spontaneously approach a limiting thickness of bimolecular dimensions (bilayers). This paper describes apparatus and methods for studying such thin lipid membranes, and illustrates their use in determining some of the basic properties of the membranes, especially bilayers. Several methods of forming thin lipid membranes are described. The early stages in apparatus development are traced, and the theoretical variables and operational parameters relating to apparatus and system design are discussed. Designs for two basic types of apparatus are presented in detail: one is a cylindrical chamber especially constructed to permit optical investigation of the membrane; the second is a multiple chamber system designed for the study of several different membranes either simultaneously or in rapid succession. Interchangeable chamber units are held in a thermostat block, and assemblies of electrodes and provisions for perfusion or sampling of aqueous medium are placed in the chambers as required. Methods are described which enable simultaneous mechanical, electrical, optical, and chemical operations and studies to be performed on the same membrane with either type of apparatus. Membranes were formed from several purified amphiphilic lipids and from mixed-lipid extracts from a variety of biological membranes. The types and mechanisms of drainage of thin lipid membranes with aqueous interfaces are analogous to those previously described for aqueous soap films in air. The limiting bilayer thickness is confirmed by electrical measurements. The resistivity of the bilayers is ca. 10¹² to 10¹⁴ ohm-cm, their capacity is ca. 0.4 μfd-cm⁻² and their dielectric breakdown voltage is ca. 3×10⁵ V-cm⁻¹. Other physical properties of the bilayers are described. Permeability of the bilayers to various substances was determined by diffusion flux, osmotic flux, and electrochemical potential methods using the apparatus described. Substances studied included water, small monovalent ions, glucose, acetylcholine, salicylamide and synaptic vesicles. The chemical, physical, electrical, and permeability properties of the experimentally formed lipid bilayer membranes are similar to those of biological membranes. These similarities strongly support the Danielli-Davson hypothesis, which proposes that a lipid bilayer is the basic structure of biological membranes. The apparatus, methods, and information presented in this paper provide tools for further investigation of lipid bilayer membrane properties and for further testing of hypotheses relating to membranes. Portions of this material are from a dissertation presented in partial fulfillment of requirements for the PhD degree, Graduate School of Arts and Sciences, Washington University.     

动态表面张力破裂磷脂膜的分子动力学模拟

磷脂双层膜在生物传感器、仿生膜和生物膜反应器等领域具有广阔的应用前景。揭示磷脂膜破裂过程规律对于磷脂膜器件设计和应用具有重要的基础意义。以二棕榈酰磷脂酰胆碱(dipalmitoyl phosphatidylcholine, DPPC)和二棕榈酰磷脂酰甘油(dipalmitoyl phosphoglycerol, DPPG)作为磷脂膜组分,采用粗粒化分子动力学模拟研究了磷脂膜组成对其破裂过程的影响规律。首先建立了磷脂膜破裂动力学的临界破裂时间及临界破裂表面张力的识别方法;进而考察了磷脂膜组成对其破裂动力学的影响规律。模拟结果表明随着带负电组分DPPG 含量增加,磷脂膜平均临界破裂时间延迟且分布变宽,即磷脂膜强度提高,磷脂膜破裂呈现非均匀特性。提出了描述动态表面张力作用下磷脂膜破裂过程的"动态"微观对抗理论,由该理论可预期磷脂膜的线张力随着DPPG 含量提高而增强,与分子动力学模拟结果相符。为基于磷脂膜的分子器件的设计提供了数值模拟及理论依据。     

Electrochemical behavior of C60 films and C60/lipid films in ionic liquids

Cyclic voltammograms (CVs) of C₆₀ films and C₆₀ embedded in cast films of triple-tailed cationic surfactant solutions and salt-free zero-charged cationic/anionic (catanionic) surfactant vesicles on glassy carbon electrode in a typical room-temperature ionic liquid (RT-IL), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), were examined. CVs show typically electrochemical oxidation and reduction. The salt-free zero-charged catanionic surfactant bilayer vesicles were determined by freeze-fracture transmission electron microscopy (FF-TEM) images and small-angle X-ray scattering (SAXS) measurements. The cast films of the salt-free zero-charged catanionic surfactant vesicles incorporated C₆₀ molecules were employed to study the electrochemical properties in RT-ILs, which would open new fields for the bulk electronic properties of fullerenes or their derivatives in ionic liquids.     

Fabrication of CaCO3-Coated Vesicles by Biomineralization and Their Application as Carriers of Drug Delivery Systems

We fabricated CaCO₃-coated vesicles as drug carriers that release their cargo under a weakly acidic condition. We designed and synthesized a peptide lipid containing the Val-His-Val-Glu-Val-Ser sequence as the hydrophilic part, and with two palmitoyl groups at the N-terminal as the anchor groups of the lipid bilayer membrane. Vesicles embedded with the peptide lipids were prepared. The CaCO₃ coating of the vesicle surface was performed by the mineralization induced by the embedded peptide lipid. The peptide lipid produced the mineral source, CO₃²⁻, for CaCO₃ mineralization through the hydrolysis of urea. We investigated the structure of the obtained CaCO₃-coated vesicles using transmission electron microscopy (TEM). The vesicles retained the spherical shapes, even in vacuo. Furthermore, the vesicles had inner spaces that acted as the drug cargo, as observed by the TEM tomographic analysis. The thickness of the CaCO₃ shell was estimated as ca. 20 nm. CaCO₃-coated vesicles containing hydrophobic or hydrophilic drugs were prepared, and the drug release properties were examined under various pH conditions. The mineralized CaCO₃ shell of the vesicle surface was dissolved under a weakly acidic condition, pH 6.0, such as in the neighborhood of cancer tissues. The degradation of the CaCO₃ shell induced an effective release of the drugs. Such behavior suggests potential of the CaCO₃-coated vesicles as carriers for cancer therapies.     

Rab27 GTPases Distribute Extracellular Nanomaps for Invasive Growth and Metastasis: Implications for Prognosis and Treatment

The Rab27 family of small GTPases regulates exocytosis of distinct vesicle types including multivesicular endosomes, which results in the release of exosomes. Exosomes are nanometer-sized membrane vesicles that enclose soluble factors such as proteins and nucleic acids within a lipid bilayer and can travel toward distant tissues to influence multiple aspects of cell behavior. In our view that tumors are endocrine organs producing exosomes, Rab27 GTPases and their effector proteins are critical determinants for invasive growth and metastasis. Rab27 proteins and their effectors may serve as prognostic biomarkers or as targets for patient-tailored therapy.     

A molecular dynamics simulation of the mechanical characteristics of a C60-filled carbon nanotube under nanoindentation using various carbon nanotube tips

The mechanical characteristics of a single-walled carbon nanotube (SWCNT) filled with C₆₀ fullerene subject to nanoindentation is studied using molecular dynamics (MD) simulations. The effects of temperature, indentation velocity, adhesion, and tip sizes were evaluated. The simulated results clearly show that the exerted load, Young’s modulus, elastic energy, and plastic energy decrease significantly with increasing temperature and decreasing indentation velocity and tip size. C₆₀ fullerenes can effectively increase the mechanical strength of a SWCNT because they act as a “barrier” to resist the radial deformation, as well as an inner wall in a double-walled carbon nanotube. With the same indentation depth, the ratio of elastic energy to plastic energy for a material gradually increases with the increase in the radius of the tip. This indicates that the elastic recovery of a material is better when the tip has a larger radius.     

Polyunsaturation in cell membranes and lipid bilayers and its effects on membrane proteins

The effect of variation of the degree ofcis-unsaturation on cell membrane protein functioning was investigated using a model lipid bilayer system and protein kinase C (PKC). This protein is a key element of signal transduction. Furthermore it is representative of a class of extrinsic membrane proteins that show lipid dependent interactions with cell membranes. To test for dependence of activity on the phospholipid unsaturation, experiments were devised using a vesicle assay system consisting of phosphatidylcholine (PC) and phosphatidylserine (PS) in which the unsaturation was systematically varied. Highly purified PKCα and ε were obtained using the baculovirus-insect cell expression system. It was shown that increased PC unsaturation elevated the activity of PKCα. By contrast, increasing the unsaturation of PSdecreased the activity of PKCα, and to a lesser extent PKCε. This result immediately rules out any single lipid bilayer physical parameter, such as lipid order, underlying the effect. It is proposed that while PC unsaturation effects are explainable on the basis of a contribution to membrane surface curvature stress, the effects of PS unsaturation may be due to specific protein-lipid interactions. Overall, the results indicate that altered phospholipid unsaturation in cell membranes that occurs in certain disease states such as chronic alcoholism, or by dietary manipulations, are likely to have profound effects on signal transduction pathways involving PKC and similar proteins.     

Docosahexaenoic acid increases permeability of lipid vesicles and tumor cells

Docosahexaenoic acid (DHA), a long-chain polyunsaturated ω3 fatty acid, is tested to determine its mode of action as an anti-cancer agent. We demonstrate that DHA can increase the permeability of phospholipid vesicles, as monitored by vesicle swelling in isomolar erythritol and leakage of sequestered carboxylfluorescein, and T27A tumor cells, as monitored by swelling in isomolar erythritol and release of sequestered⁵¹Cr. DHA was incorporated into lipid vesicles as either the free fatty acid or as 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine. DHA was incorporated into the tumor cells by fusion with vesicles made from the mixed-chain phosphatidylcholines. DHA is demonstrated here to be much more effective in increasing permeability than is oleic acid, the major unsaturated fatty acid normally found in tumor plasma membranes. It is proposed that incorporation of DHA makes tumor plasma membranes substantially more permeable, which may explain, in part, its anti-tumor properties.     

Availability of lysophosphatidylcholine in single bilayer vesicles for hydrolysis by lysophospholipase

Single bilayer vesicles were prepared from total rat liver microsomal lipids to which 5 mol% lysophosphatidylcholine had been added. The availability of lysophosphatidylcholine for enzymatic hydrolysis by lysophospholipase (EC 3.1.1.5) was found to be higher in vesicles prepared by the cholate dispersion technique when compared with sonicated vesicles. Sepharose 4 B chromatography showed that the vesicles prepared by the cholate technique were smaller than those prepared by sonication. This is in contrast to previous observations for egg phosphatidylcholine vesicles. Total rat liver microsomal extracts were found to contain proteolipid, which could be removed by ether precipitation. Cholate vesicles prepared from proteolipid-free extracts were still smaller than sonicated vesicles from this extract. Experiments with [¹⁴C] dextran entrapped in the vesicles indicate that there is no loss of the permeability barrier of the vesicles for high molecular weight solutes during vesicle treatment with lysophospholipase. The high availability of lysophosphatidylcholine in cholate vesicles of total rat liver microsomal lipids is discussed in terms of a highly asymmetric distribution of lysophosphatidylcholine over the inner and outer monolayer of the bilayer.     

Chemical approaches to triggerable lipid vesicles for drug and gene delivery

Effective drug delivery requires the precise spatial and temporal delivery of therapeutic agents to the target site. To this end, a variety of chemical and physicochemical approaches have been devised to create lipid vesicles (liposomes) that can be triggered to release their contents in a controlled fashion. The triggers include changes in pH, redox potential, temperature, or the level of specific enzymes. We review the chemistries that have recently been applied to exploit the pH and redox potential triggers so as to release vesicle contents in the appropriate biological location.     

Soft vesicles in the synthesis of hard materials

Vesicles of surfactants in aqueous solution have received considerable attention because of their use as simple model systems for biological membranes and their applications in various fields including colloids, pharmaceuticals, and materials. Because of their architecture, vesicles could prove useful as "soft" templates for the synthesis of "hard materials". The vesicle phase, however, has been challenging and difficult to work with in the construction of hard materials. In the solution-phase synthesis of various inorganic or macromolecular materials, templating methods provide a powerful strategy to control the size, morphology, and composition of the resulting micro- and nanostructures. In comparison with hard templates, soft templates are generally constructed using amphiphilic molecules, especially surfactants and amphiphilic polymers. These types of compounds offer advantages including the wide variety of available templates, simple fabrication processes under mild conditions, and easy removal of the templates with less damage to the final structures. Researchers have used many ordered molecular aggregates such as vesicles, micelles, liquid crystals, emulsion droplets, and lipid nanotubes as templates or structure-directing agents to control the synthesis or assembly hard micro- and nanomaterials composed from inorganic compounds or polymers. In addition to their range of sizes and morphologies, vesicles present unique structures that can simultaneously supply different microenvironments for the growth and assembly of hard materials: the inner chamber of vesicles, the outer surface of the vesicles, and the space between bilayers. Two main approaches for applying vesicles in the field of hard materials have been explored: (i) in situ synthesis of micro- or nanomaterials within a specific microenvironment by vesicle templating and (ii) the assembly or incorporation of guest materials during the formation of vesicles. This Account provides an in-depth look at the research concerning the association of soft vesicles with hard materials by our laboratory and others. We summarize three main principles of soft vesicle usage in the synthesis of hard materials and detailed procedures for vesicle templating and the characterization of the synthetic mechanisms. By use of these guiding principles, a variety of inorganic materials have been prepared, such as quantum dots, noble metal nanoparticles, mesoporous structures, and hollow capsules. Polymerization within the vesicle bilayers enhances vesicle stability, and this strategy has been developed to synthesize hollow polymer materials. Since 2004, our group has pursued a completely different strategy in the synthesis of micro- and nanomaterials using vesicles as reactive templates. In this method, the vesicles act not only as templates but also as reactive precursors. Because of the location of metal ions on the bilayer membranes, such reactions are restricted to the interface of the vesicle membrane and solution. Finally, using the perspective of soft matter chemistry, we stress some basic criteria for vesicle templating.