159,835 research outputs found
Liposomes encapsulating polymeric chitosan based vesicles - a vesicle in vesicle system for drug delivery
Drug delivery systems comprising vesicles prepared from one amphiphile encapsulating vesicles prepared from a second amphiphile have not been prepared previously due to a tendency of the bilayer components of the different vesicles to mix during preparation. Recently we have developed polymeric vesicles using the new polymer-palmitoyl glycol chitosan and cholesterol in a 2:1 weight ratio. These polymeric vesicles have now been encapsulated within egg phosphatidylcholine (egg PC), cholesterol (2:1 weight ratio) liposomes yielding a vesicle in vesicle system. The vesicle in vesicle system was visualised by freeze fracture electron microscopy. The mixing of the different bilayer components was studied by monitoring the excimer fluorescence of pyrene-labelled polymeric vesicles after their encapsulation within egg PC liposomes or hexadecyl diglycerol ether niosomes. A minimum degree of lipid mixing was observed with the polymeric vesicle-egg PC liposome system when compared to the polymeric vesicle-hexadecyl diglycerol ether niosome system. The polymeric vesicle-egg PC vesicle in vesicle system was shown to retard the release of encapsulated solutes. 28% of 5(6)-carboxyfluorescein (CF) encapsulated in the polymeric vesicle compartment of the vesicle in vesicle system was released after 4 h compared to the release of 62% of encapsulated CF from plain polymeric vesicles within the same time period
Soft Confinement for Polymer Solutions
As a model of soft confinement for polymers, we investigated equilibrium
shapes of a flexible vesicle that contains a phase-separating polymer solution.
To simulate such a system, we combined the phase field theory (PFT) for the
vesicle and the self-consistent field theory (SCFT) for the polymer solution.
We observed a transition from a symmetric prolate shape of the vesicle to an
asymmetric pear shape induced by the domain structure of the enclosed polymer
solution. Moreover, when a non-zero spontaneous curvature of the vesicle is
introduced, a re-entrant transition between the prolate and the dumbbell shapes
of the vesicle is observed. This re-entrant transition is explained by
considering the competition between the loss of conformational entropy and that
of translational entropy of polymer chains due to the confinement by the
deformable vesicle. This finding is in accordance with the recent experimental
result reported by Terasawa, et al.Comment: 5 pages, 3 figure
Activity-dependence of synaptic vesicle dynamics
The proper function of synapses relies on efficient recycling of synaptic vesicles. The small size of synaptic boutons has hampered efforts to define the dynamical states of vesicles during recycling. Moreover, whether vesicle motion during recycling is regulated by neural activity remains largely unknown. We combined nanoscale-resolution tracking of individual synaptic vesicles in cultured hippocampal neurons from rats of both sexes with advanced motion analyses to demonstrate that the majority of recently endocytosed vesicles undergo sequences of transient dynamical states including epochs of directed, diffusional, and stalled motion. We observed that vesicle motion is modulated in an activity-dependent manner, with dynamical changes apparent in ∼20% of observed boutons. Within this subpopulation of boutons, 35% of observed vesicles exhibited acceleration and 65% exhibited deceleration, accompanied by corresponding changes in directed motion. Individual vesicles observed in the remaining ∼80% of boutons did not exhibit apparent dynamical changes in response to stimulation. More quantitative transient motion analyses revealed that the overall reduction of vesicle mobility, and specifically of the directed motion component, is the predominant activity-evoked change across the entire bouton population. Activity-dependent modulation of vesicle mobility may represent an important mechanism controlling vesicle availability and neurotransmitter release.SIGNIFICANCE STATEMENTMechanisms governing synaptic vesicle dynamics during recycling remain poorly understood. Using nanoscale resolution tracking of individual synaptic vesicles in hippocampal synapses and advanced motion analysis tools we demonstrate that synaptic vesicles undergo complex sets of dynamical states that include epochs of directed, diffusive, and stalled motion. Most importantly, our analyses revealed that vesicle motion is modulated in an activity-dependent manner apparent as the reduction in overall vesicle mobility in response to stimulation. These results define the vesicle dynamical states during recycling and reveal their activity-dependent modulation. Our study thus provides fundamental new insights into the principles governing synaptic function
Two-dimensional Vesicle dynamics under shear flow: effect of confinement
Dynamics of a single vesicle under shear flow between two parallel plates is
studied using two-dimensional lattice-Boltzmann simulations. We first present
how we adapted the lattice-Boltzmann method to simulate vesicle dynamics, using
an approach known from the immersed boundary method. The fluid flow is computed
on an Eulerian regular fixed mesh while the location of the vesicle membrane is
tracked by a Lagrangian moving mesh. As benchmarking tests, the known vesicle
equilibrium shapes in a fluid at rest are found and the dynamical behavior of a
vesicle under simple shear flow is being reproduced. Further, we focus on
investigating the effect of the confinement on the dynamics, a question that
has received little attention so far. In particular, we study how the vesicle
steady inclination angle in the tank-treading regime depends on the degree of
confinement. The influence of the confinement on the effective viscosity of the
composite fluid is also analyzed. At a given reduced volume (the swelling
degree) of a vesicle we find that both the inclination angle, and the membrane
tank-treading velocity decrease with increasing confinement. At sufficiently
large degree of confinement the tank-treading velocity exhibits a
non-monotonous dependence on the reduced volume and the effective viscosity
shows a nonlinear behavior.Comment: 12 pages, 8 figure
Dynamics of Vesicle Formation from Lipid Droplet: Mechanism and Controllability
A coarse-grained model developed by Marrink et al. [J. Phys. Chem. B 111,
7812 (2007)] is applied to investigate vesiculation of lipid
[dipalmitoylphosphatidylcholine (DPPC)] droplets in water. Three kinds of
morphologies of micelles are found with increasing lipid droplet size. When the
initial lipid droplet is smaller, the equilibrium structure of the droplet is a
spherical micelle. When the initial lipid droplet is larger, the lipid ball
starts to transform into a disk micelle or vesicle. The mechanism of vesicle
formation from a lipid ball is analyzed from the self-assembly of DPPC on the
molecular level, and the morphological transition from disk to vesicle with
increasing droplet size is demonstrated. Importantly, we discover that the
transition point is not very sharp, and for a fixed-size lipid ball, the disk
and vesicle appear with certain probabilities. The splitting phenomenon, i.e.,
the formation of a disk/vesicle structure from a lipid droplet, is explained by
applying a hybrid model of the Helfrich membrane theory. The elastic module of
the DPPC bilayer and the smallest size of a lipid droplet for certain formation
of a vesicle are successfully predicted.Comment: 22 pages, 11 figures Submitted to J. Chem. Phy
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