Vesicle Shape Research Articles

Paramonostomum bubaki n. sp. (Digenea: Notocotylidae) from the Black Coot, Fulica atra (Gruiformes: Rallidae), in South Central Pakistan

During a helminthological survey of black coot, Fulica atra (Gruiformes: Rallidae), in Sindh Province of Pakistan, eight specimens of undescribed species of trematode belonging to genus Paramonostomum Lühe, 1909 were recovered from large intestine of the single host bird. Paramonostomum bubaki n. sp. differs from its congeners except P. macrovesiculum Dharejo et al., 2006 by having less attenuated anterior end, a pharynx, a bifurcal genital pore, a longer posttesticular space, a Y-shaped excretory vesicle, number of uterine loops (16), and large size of filamentous eggs. P. bubaki n. sp. resembles P. macrovesiculum Dharejo et al., 2006 collected from Fulica atra from Pakistan by having a pharynx but differs in larger body, smaller esophagus, a bifurcal genital pore, shape of cirrus sac, seminal vesicle and gonads, ceca reaching posterior extremity, and a longer posttesticular space.

Relating vesicle shapes in pyroclasts to eruption styles

Vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions. Although their numbers and sizes are used routinely to infer aspects of eruption dynamics, vesicle shape remains an underutilized parameter. We have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles, using the dimensionless shape factor $\Omega $ , a measure of the degree of complexity of the bounding surface of an object. For each of the seven eruptions, we have also estimated the capillary number, Ca, from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling. We find that $\Omega $ is smaller for eruptions with ${\rm{Ca}} \ll 1$ than for eruptions with Ca $\gg 1$ . Consistent with previous studies, we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth, such as coalescence and shape relaxation of bubbles by capillary stresses. Among the samples analyzed, Strombolian and Hawaiian fire-fountain eruptions have ${\rm{Ca}} \ll 1$ , in contrast to Vulcanian, Plinian, and ultraplinian eruptions. Interestingly, the basaltic Plinian eruptions of Tarawera volcano, New Zealand in 1886 and Mt. Etna, Italy in 122 BC, for which the cause of intense explosive activity has been controversial, are also characterized by ${\rm{Ca}} \gg 1$ and larger values of $\Omega $ than Strombolian and Hawaiian style (fire fountain) eruptions. We interpret this to be the consequence of syn-eruptive magma crystallization, resulting in high magma viscosity and reduced rates of bubble growth. Our model results indicate that during these basaltic Plinian eruptions, buildup of bubble overpressure resulted in brittle magma fragmentation.

Computation of Two-Phase Biomembranes with Phase DependentMaterial Parameters Using Surface Finite Elements

AbstractThe shapes of vesicles formed by lipid bilayers with phase separation are governed by a bending energy with phase dependent material parameters together with a line energy associated with the phase interfaces. We present a numerical method to approximate solutions to the Euler-Lagrange equations featuring triangulated surfaces, isoparametric quadratic surface finite elements and the phase field approach for the phase separation. Furthermore, the method involves an iterative solution scheme that is based on a relaxation dynamics coupling a geometric evolution equation for the membrane surface with a surface Allen-Cahn equation. Remeshing and grid adaptivity are discussed, and in various simulations the influence of several physical parameters is investigated.

Contrasting patterns of vesiculation in low, intermediate, and high Hawaiian fountains: A case study of the 1969 Mauna Ulu eruption

Hawaiian-style eruptions, or Hawaiian fountains, typically occur at basaltic volcanoes and are sustained, weakly explosive jets of gas and dominantly coarse, juvenile ejecta (dense spatter to delicate reticulite). Almost the entire range of styles and mass eruption rates within Hawaiian fountaining occurred during twelve fountaining episodes recorded at Mauna Ulu, Kīlauea between May and December 1969. Such diversity in intensity and style is controlled during magma ascent by many processes that can be constrained by the size and shape of vesicles in the 1969 pyroclasts. This paper describes pyroclast vesicularity from high, intermediate, and low fountaining episodes with eruption rates from 0.05 to 1.3×106m3h−1. As each eruptive episode progressed, magma ascent slowed in and around the vent system, offering extended time for bubbles to grow and coalesce. Late ejected pyroclasts are thus characterized by populations of fewer and larger vesicles with relaxed shapes. This progression continued in the intervals between episodes after termination of fountain activity. The time scale for this process of shallow growth, coalescence and relaxation of bubbles is typically tens of hours. Rims and cores of pumiceous pyroclasts from moderate to high fountaining episodes record a second post-fragmentation form of vesicle maturation. Partially thermally insulated pyroclasts can have internal bubble populations evolve more dynamically with continued growth and coalescence, on a time scale of only minutes, during transport in the fountains. Reticulite, which formed in a short-lived fountain 540m in height, underwent late, short-lived bubble nucleation followed by rapid growth of a uniform bubble population in a thermally insulated fountain, and quenched at the onset of permeability before significant coalescence. These contrasting patterns of shallow degassing and outgassing were the dominant controls in determining both the form and duration of fountaining episodes at Mauna Ulu, and probably for many other Hawaiian-style eruptions.

Field theoretical approach for a polymer-containing vesicle

We simulate the structure of a vesicle that encloses polymers as an example of endocytosis and exocytosis. Simulations are performed by coupling two types of continuum field methods, i.e. the phase field theory for vesicle shape and the self-consistent field theory for polymer conformation. Comparing free energies between prolate and oblate shapes of vesicles as the candidates of equilibrium shape of the vesicle that contains polymers, we show that prolate shape is more stable, where the dominant contribution is the conformation entropy of polymers. We extend the above static simulation to a dynamic one by introducing a flow field that is described by Navier–Stokes equation.

Highly vesicular pumice generated by buoyant detachment of magma in subaqueous volcanism

Many submarine caldera volcanoes are blanketed with deposits of highly vesicular pumice, typically attributed to vigorous explosive activity1, 2, 3, 4. However, it is challenging to relate volcanic products to specific eruptive styles in submarine volcanism5, 6. Here we document vesicularity and textural characteristics of pumice clasts dredged from the submarine Macauley volcano in the Kermadec arc, southwest Pacific Ocean. We find that clasts show a bimodal distribution, with corresponding differences in vesicle abundances and shapes. Specifically, we find a sharp mode at 91% vesicularity and a broad mode at 65–80%. Subordinate clasts show gradients in vesicularity. We attribute the bimodality to a previously undocumented eruptive style that is neither effusive nor explosive. The eruption rate is insufficient to cause magma to fragment explosively, yet too high to passively feed a lava dome. Instead, the magma foam buoyantly detaches at the vent and rises as discrete magma parcels, or blebs, while continuing to vesiculate internally. The blebs are widely distributed by ocean currents before they disintegrate or become waterlogged. This disintegration creates individual clasts from interior and rim fragments, yielding the bimodal vesicularity characteristics. We conclude that the generation and widespread dispersal of highly vesicular pumice in the marine environment does not require highly explosive activity.

Nano-Carrier for Accentuated Transdermal Drug Delivery

This research objective was to design a nano-carrier for Glibenclamide (GBD) by loading it in to nano-transfersomes to provide an accentuated transdermal drug delivery for Non-Insulin Dependent Diabetes Mellitus (NIDDM) The nanotransfersomes were prepared by sonication method and optimized using a statistically three-factor three-level Factorial Design (Box-Behnken design). A second order equation (polynomial) was originated and construct contour plots (2- D) for prediction the responses and characterized by various parameters (i.e. entrapment efficiency, vesicle shape & size, zeta potential, degree of deformability, permeation and skin irritation study). The skin permeation of optimized formulation (GNTs2) was found to be significantly higher (enhancement ratio is 10.44) than the drug in solution and also further confirmed by fluorescence microscopy using due i.e. Rhodamine B. Hence, drug loaded nano-transfersomes accentuates its transdermal flux and can be used as a nano-vehicle for NIDDM.

Transient oscillation of shape and membrane conductivity changes by field pulse-induced electroporation in nano-sized phospholipid vesicles

The results of electrooptical and conductometrical measurements on unilamellar lipid vesicles (of mean radius a = 90 nm), filled with 0.2 M NaCl solution, suspended in 0.33 M sucrose solution of 0.2 mM NaCl, and exposed to a stepwise decaying electric field (time constant τE = 154 μs) in the range 10 ≤ E0 (kV cm(-1)) ≤ 90, are analyzed in terms of cyclic changes in vesicle shape and vesicle membrane conductivity. The two peaks in the dichroitic turbidity relaxations reflect two cycles of rapid membrane electroporation and slower resealing of long-lived electropores. The field-induced changes reflect structural transitions between closed (C) and porated (P) membrane states, qualified by pores of type P1 and of type P2, respectively. The transient change in the membrane conductivity and the transient shape oscillation are based on changes in the pore density of the (larger) P2-pores along a hysteresis cycle. The P2-pore formation leads to transient net ion flows across the P2-pores and to transient changes in the membrane field. The kinetic data are numerically processed in terms of coupled structural relaxation modes. Using the torus-hole pore model, the mean inner pore radii are estimated to be r1 = 0.38 (±0.05) nm and r2 = 1.7 (±0.1) nm, respectively. The observation of a transient oscillation of membrane electroporation and of shape changes in a longer lasting external field pulse is suggestive of potential resonance enhancement, for instance, of electro-uptake by, and of electro-release of biogenic molecules from, biological cells in trains of long-lasting low-intensity voltage pulses.

Monte Carlo simulations of a polymer confined within a fluid vesicle

Monte Carlo simulations are employed to study a fluid vesicle that contains a single worm-like polymer chain. The contour length of the polymer is about five times the circumference of the nominally spherical vesicle. We vary the degree of polymer confinement in our simulations by increasing the persistence length of the polymer. The vesicle is represented by a randomly triangulated self-avoiding network that can undergo bending deformations. Upon increasing the persistence length of the polymer beyond the size of the vesicle, we observe a transition of the polymer from an isotropic disordered random conformation to an ordered toroidal coil. Concomitantly, the vesicle adopts an oblate shape to allow for some expansion of the polymer coil inside the vesicle. It is convenient to characterize both polymer and vesicle in terms of the asphericity, a quantity derived from the gyration tensor. At the onset of the polymer's ordering transition, the asphericity passes through a minimum for both polymer and vesicle. The increase in vesicle asphericity for a semi-flexible polymer can be understood in terms of ground state energy calculations, either for a simplified representation of the vesicle shape (we specifically discuss a disk shape with a semi-toroidal rim) or involving a full vesicle shape optimization. The asphericity of the polymer coil results from conformational fluctuations and can be rationalized using Odijk's deflection length of strongly curved semi-flexible polymers.

Shape transformations of bilayer vesicles from amphiphilic block copolymers: a dissipative particle dynamics simulation study

Dissipative particle dynamics (DPD) simulations are employed to study the shape transformations of vesicles formed from amphiphilic triblock copolymers. The amphiphilic molecule is built from two different hydrophilic blocks on the sides and a hydrophobic block in the middle. To model the asymmetric membrane in the vesicle, spontaneous curvature is introduced by the difference in repulsive parameters between the two different hydrophilic blocks of the amphiphilic molecule. A plethora of complex vesicle shapes is revealed by the DPD simulations, including some shapes that have not been reported in other simulation studies on vesicles, such as starfish-shaped, toroidal, long rodlike, and inverted vesicles. These simulated vesicles agree with theoretically derived vesicle shapes based on the spontaneous curvature model and also with experimental observations.

Submicron hybrid vesicles consisting of polymer–lipid and polymer–cholesterol blends

Hybrid polymer–lipid and polymer–cholesterol submicron unilamellar vesicles with a diameter of ∼200 nm based on poly(dimethylsiloxane)-block-poly(2-methyl-oxazoline) (PDMS-b-PMOXA) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were prepared by using the film-hydration and extrusion method. The vesicles were extensively characterized via dynamic and static light scattering (DLS and SLS), dual-color fluorescence cross-correlation spectroscopy (DC-FCCS), cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy imaging and force spectroscopy (AFM). The combination of these techniques provides information about the vesicle size, shape and long-term stability as well as the mechanical properties. DC-FCCS proved the formation of hybrid vesicles containing both components. Cryo-TEM and AFM studies revealed that the presence of cholesterol in vesicle membranes leads to a higher packing density resulting in a reduced membrane thickness and a significantly increased bending stiffness compared to pure polymersomes and polymer–lipid vesicles.

Photo-induced reversible uniform to Janus shape change of vesicles composed of PNIPAM-b-PAzPy2

In this work, three kinds of vesicles are fabricated by the self-assembly of amphiphilic block copolymers (BCPs), in which the hydrophobic chains are side chain azobenzene polymers with spacers of 0, 2 and 6 methylene units, respectively. It has been found that vesicles formed by BCPs with a spacer of 0 methylene units have no photo-responsive behavior and vesicles with a spacer of 6 have a photo-induced swelling behavior under the irradiation of light at 365 nm. Unexpectedly, the vesicle formed by BCPs with a spacer of 2 shows a photo-induced reversible uniform to Janus shape change under the same irradiation. This reversible process means that a bistable shape change of the vesicle can be controlled by the switching of UV light. A UV-visible absorption spectrum and a laser-trapped Raman spectrum (LTRS) are used to investigate differences in the morphology and photo-induced behavior of these vesicles. Results have confirmed that the photo-induced Janus shape of vesicles formed by BCPs with a spacer of 2 is a metastable shape, different from the stable Janus shape of vesicles formed by BCPs with a spacer of 0. This is also testified by a two-photon confocal laser scanning microscope (CLSM). From the results it is realized that the spacer length in the hydrophobic chains of BCPs can affect the photo-induced behavior of vesicles formed by BCPs, which will be a key point in designing functional vesicles with special morphologies.

Design and development of cefdinir niosomes for oral delivery

Objective:The aim of the present study was to develop nonionic surfactant based vesicles (niosomes) to improve poor and variable oral bioavailability of cefdinir.Materials and Methods:Cefdinir niosomes were formulated by sonication method using varying concentration of surfactant (span 60), with and without soya lecithin, but the cholesterol ratio was kept constant in all the formulations. The influence of formulation variables such as surfactant concentration, soya lecithin presence or absence were optimized for size and entrapment efficiency. Drug excipient interaction studies were performed using FTIR, indicating compatibility of excipients with drug.Results:The highest entrapment efficiency (74.56%) was observed when span 60, cefdinir, cholesterol and soya lecithin were used in the ratio of 5:1:1:1. The zeta sizer of the niosomal formulations showed the size range between 190 nm-1140 nm. The photomicrography showed round shape of vesicles and further nano size of niosomes was confirmed by scanning and transmission electron microscopy. The optimized niosomal formulations (F11 and F6) exhibited sustained in-vitro release of 94.91% and 94.07% respectively upto 12 h. The ex-vivo permeation studies of optimized formulation revealed that the niosomal dispersion improved cefdinir permeability across goat intestinal membrane as compared to plain drug solution and marketed suspension (Adcef®). Antimicrobial activity studies revealed that the niosomes potentiated bacteriostatic activity of cefdinir as compared to Adcef®.Conclusion:The niosomal formulation could be one of the promising delivery system for cefdinir with improved oral bioavailability and controlled drug release profile.

A dissipative dynamical method based on discrete variational principle：stationary shapes of three-dimensional vesicle

In this article, the dissipative dynamical evolution method based on the discrete variational principle is applied to a three-dimensional (3D) vesicle system. The stationary shapes of vesicles are obtained through the minimization of membrane bending energy without any symmetric assumption, which is an outstanding merit of our method. Aiming at a 3D vesicle system with certain parameter settings, a series of axisymmetric shapes are achieved by our method. The simulation results are in good agreement with those obtained with axisymmetric assumption, which indicates that our method can describe the deformation of 3D vesicle with extremely high precision. In addition, a shape transition between two stable states with great difference is studied, which further implies the capability of our proposed method in simulating large deformations regarding the 3D membrane. We believe that we have provided a very powerful simulation method for the future studies of bio-membrane deformations.

Amplification of Thermal Noise by Vesicle Dynamics

A novel noise amplification mechanism resulting from the interaction of thermal fluctuations and nonlinear vesicle dynamics is reported. It is observed in a time-dependent vesicle state called trembling (TR). High spatial resolution and very long time series of TR compared to the vesicle period allow us to quantitatively analyze the generation and amplification of spatial and temporal modes of the vesicle shape perturbations. During a compression part of each TR cycle, a vesicle finds itself on the edge of the wrinkling instability, where thermally excited spatial modes are amplified.

Experimental study of the bending elasticity of charged lipid bilayers in aqueous solutions with pH5

Exposure to high concentrations of contaminations due to air polluting gases, vapours and aerosols and possibly altering the normal pH in the body could lead to undesirable changes in the properties of biological cells. Here, we study experimentally the mechanical properties of synthetic phospholipid bilayers containing increasing molar fractions (up to 0.15) of charged lipid (synthetic phosphatidylserine) in aqueous solutions with controlled ionic strength and at pH 5, which is slightly lower than the physiological values of pH. Our observations in phase contrast and fluorescence testified to the coexistence of two phases in membranes for temperatures below 29°C. Micro-sized inhomogeneities in vesicle membranes were systematically observed at temperatures lower than 29°C and for molar fractions of phosphatidylserine in the bilayer higher than 0.1. For the quantitative determination of the membrane bending rigidity, we applied thermal fluctuation analysis of the shape of quasispherical lipid vesicles. As far as the liquid-crystalline state of the bilayer is a necessary condition for the application of the experimental method, only vesicles satisfying this requirement were processed for determination of their membrane bending rigidity. The value obtained for the bending modulus of bilayers with 0.15 molar content of charged lipid is about two times higher than the bending modulus of uncharged membranes in the same bathing solution. These findings are in qualitative agreement with our previous results for the bending rigidity of charged bilayers, measured by vesicle micromanipulation.

Membrane properties revealed by spatiotemporal response to a local inhomogeneity

We study theoretically the spatiotemporal response of a lipid membrane submitted to a local chemical change of its environment, taking into account the time-dependent profile of the reagent concentration due to diffusion in the solution above the membrane. We show that the effect of the evolution of the reagent concentration profile becomes negligible after some time. It then becomes possible to extract interesting properties of the membrane response to the chemical modification. We find that a local density asymmetry between the two monolayers relaxes by spreading diffusively in the whole membrane. This behavior is driven by intermonolayer friction. Moreover, we show how the ratio of the spontaneous curvature change to the equilibrium density change induced by the chemical modification can be extracted from the dynamics of the local membrane deformation. Such information cannot be obtained by analyzing the equilibrium vesicle shapes that exist in different membrane environments in light of the area-difference elasticity model.

AUTOCOUNTER, an ImageJ JavaScript to analyze LC3B-GFP expression dynamics in autophagy-induced astrocytoma cells

An ImageJ JavaScript, AUTOCOUNTER, was specifically developed to monitor and measure LC3B-GFP expression in living human astrocytoma cells, namely T98G and U373-MG. Discrete intracellular GFP fluorescent spots derived from transduction of a Baculovirus replication-defective vector (BacMam LC3B-GFP), followed by microscope examinations at different times. After viral transgene expression, autophagy was induced by Rapamycin administration and assayed in ph-p70S6K/ p70S6K and LC3B immunoblotting expression as well as by electron microscopy examinations. A mutated transgene, defective in LC3B lipidation, was employed as a negative control to further exclude fluorescent dots derived from protein intracellular aggregation. The ImageJ JavaScript was then employed to evaluate and score the dynamics changes of the number and area of LC3B-GFP puncta per cell in time course assays and in complex microscope examinations. In conclusion, AUTOCOUNTER enabled to quantify LC3B-GFP expression and to monitor dynamics changes in number and shapes of autophagosomal-like vesicles: it might therefore represent a suitable algorithmic tool for in vitro autophagy modulation studies.

Development, Characterization, and Evaluation of Liposomes and Niosomes of Bacitracin Zinc

The skin permeation of bacitracin zinc in liposomes and niosomes after topical application were elucidated in the present study with the to increase its penetration capacity and, hence, efficiency. The formulations of bacitracin zinc were prepared by film hydration method and characterized for vesicle shape, size, entrapment efficiency, and drug permeation across rat skin and also evaluated for their stability. Formulation with niosomes demonstrated a better skin permeation potential, sustained release characteristic, and higher stability as compared to liposomes. The ability of liposomes and niosomes to modulate drug delivery makes the two vesicles useful to formulate topical bacitracin zinc.

Formation mechanisms and control factors of vesicular soil structure

Abstract Vesicular structure is a widespread feature of soils in arid environments. Typically associated with stone pavements, it has a major control function for dust and water fluxes and, hence, for site ecology. Previous models of vesicular structure formation and stability are inconsistent and mostly focused on the investigation of isolated control parameters. To test existing models, to infer plausible mechanisms of vesicular structure formation and to unveil controlling environmental and sedimentological parameters, we present quantitative data of vesicle properties of artificial and natural vesicles. Vesicles are not unstable but their changes in size are non-linear with time. They form due to surface sealing by puddling and by a wetting front, which advances downward, thereby elevating gas pressure within the sediment matrix. Translocation of clay or precipitation of calcium carbonate support vesicle stabilisation. Vesicular structure forms within a wide range of environmental and sedimentological settings: at least 6.3–15.7 mm of water per wetting cycle, 0–70% sand content, 0.8–5.6 mS/cm electric conductivity and 1–28% calcium carbonate content. High sand contents favour larger and rounder vesicles, whereas increasing calcium carbonate content has the opposite effect. The concentration of dissolved ions does not considerably influence vesicle formation. Under an artificial cover stone vesicles could not be created at all, whereas they were concentrated around stone margins. The main limiting factor for vesicle formation in natural environments is root activity. The type and density of surface cover determine fine material fluxes into the aggregates of vesicular horizons. The shape of vesicles may be related to dust influx intensity. Accordingly, horizons with spherical vesicles may indicate constant low dust influx on poorly vegetated surfaces and be, therefore, used as proxies of environmental conditions.