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1.
Conditions for self-reproduction are sought for a growing vesicle with its growth defined by an exponential increase of vesicle
membrane area and by adequate flow of the solution across the membrane. In the first step of the presumed vesicle self-reproduction
process, the initially spherical vesicle must double its volume in the doubling time of the membrane area and, through the
appropriate shape transformations, attain the shape of two equal spheres connected by an infinitesimally thin neck. The second
step involves separation of the two spheres and relies on conditions that cause the neck to be broken. In this paper we consider
the first step of this self-reproduction process for a vesicle suspended in a solution whose solute can permeate the vesicle
membrane. It is shown that vesicle self-reproduction occurs only for certain combinations of the values of membrane hydraulic
and solute permeabilities and the external solute concentration, these quantities being related to the mechanical properties
of the membrane and the membrane area doubling time. The analysis includes also the relaxation of a perturbed system towards
stationary self-reproduction behavior and the case where the final shape consists of two connected spheres of different radii. 相似文献
2.
Mader MA Ez-Zahraouy H Misbah C Podgorski T 《The European physical journal. E, Soft matter》2007,22(4):275-280
A simple 2D model of deformable vesicles tumbling in a shear under flow is introduced in order to
account for the main qualitative features observed experimentally as shear rates are increased.
The simplicity of the model allows for a full analytical
tractability while retaining the essential physical ingredients. The model reveals that the main axes of the vesicle
undergo oscillations which are coupled to the vesicle orientation in
the flow. The model reproduces and sheds light on the main novel features reported in
recent experiments [M. Mader et al., Eur. Phys. J. E. 19, 389
(2006)], namely that both coefficients A and B that enter the
Keller-Skalak equation, dψ/dt = A+Bcos(2 ψ) (ψ is
the vesicle orientation angle in the shear flow), undergo a collapse
upon increasing shear rate. 相似文献
3.
4.
Fluctuation spectra of fluid compound membrane systems are calculated. The systems addressed contain two (or more) almost
parallel membranes that are connected by harmonic tethers or by a continuous, harmonic confining potential. Additionally,
such a compound system can be attached to a supporting substrate. We compare quasi-analytical results for tethers with analytical
results for corresponding continuous models and investigate under what circumstances the discrete nature of the tethers actually
influences the fluctuations. A tethered, supported membrane pair with similar bending rigidities and stiff tethers can possess
a nonmonotonic fluctuation spectrum with a maximum. A nonmonotonic spectrum with a maximum and a minimum can occur for an
either free or supported membrane pair of rather different bending rigidities and for stiff tethers. Typical membrane displacements
are calculated for supported membrane pairs with discrete or continuous interacting potentials. Thereby an estimate of how
close the constituent two membranes and the substrate typically approach each other is given. For a supported membrane pair
with discrete or continuous interactions, the typical displacements of each membrane are altered with respect to a single
supported membrane, where those of the membrane near the substrate are diminished and those of the membrane further away are
enhanced. 相似文献
5.
Perino-Gallice L Fragneto G Mennicke U Salditt T Rieutord F 《The European physical journal. E, Soft matter》2002,8(3):275-282
Thin multilamellar assemblies of neutral lipid bilayers deposited on silicon substrates are shown to be unstable upon hydration.
We analyze the stability of these systems taking into account a reduction of the fluctuation-related components of the bilayer
interaction potential. The sizes of the patterns observed are consistent with a spinodal dewetting process.
Received 27 November 2001 相似文献
6.
R. Capovilla C. Chryssomalakos J. Guven 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):163-166
We examine the equilibria of a rigid loop in the plane, characterized by an energy functional quadratic in the curvature,
subject to the constraints of fixed length and fixed enclosed area. Whereas the only non self-intersecting equilibrium corresponding
to the fixed length constraint is the circle, the area constraint gives rise to distinct equilibria labeled by an integer.
These configurations exhibit self-intersections and bifurcations as the area is reduced. In addition, not only can the Euler-Lagrange
equation be integrated to provide a quadrature for the curvature but the embedding itself can be expressed as a local function
of the curvature. Perturbations connecting equilibria are shown to satisfy a first order ODE which is readily solved. Analytical
expressions for the energy as a function of the area are obtained in the limiting regimes.
Received 18 October 2001 / Received in final form 31 May 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: capo@fis.cinvestav.mx
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ID="b"e-mail: chryss@nuclecu.unam.mx
RID="c"
ID="c"e-mail: jemal@nuclecu.unam.mx 相似文献
7.
8.
I.M. Mladenov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):327-330
The general shape equation describing the forms of vesicles is a highly nonlinear partial differential equation for which
only a few explicit solutions are known. These solvable cases are briefly reviewed and a new analytical solution which represents
the class of the constant mean curvature surfaces is described. Pearling states of the tubular fluid membranes can be explained
as a continuous deformation preserving membrane mean curvature.
Received 2 February 2002 / Received in final form 4 February 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: mladenov@obzor.bio21.bas.bg 相似文献
9.
J. Nissen S. Gritsch G. Wiegand J.O. Rädler 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):335-344
We report on the wetting behavior of phospholipid membranes on solid surfaces immersed in aqueous solution. Using fluorescence
microscopy, the spreading velocity of fluid bilayers advancing from a lipid source is investigated. The kinetic spreading
coefficient was measured as a function of temperature for pure DMPC membranes and as a function of charge density and cholesterol
content for binary membranes. A theoretical model for the membrane flow is presented, which takes into account the liquid
crystalline bilayer architecture of the lipid membrane. The spreading power results from the membrane-solid VdW interaction
and is dissipated in hydrodynamic shear flow as well as by inter-monolayer friction within the bilayer. The frictional drag
causes a dynamic tension gradient in the spreading membrane, which is manifested by a single exponential decay of the fluorescence
intensity profile along the spreading direction. Obstacles are shown to act as pinning centers deforming the advancing line
interface. However, no depinning was observed, since the centers are circumflown without abrupt relaxation.
Received 6 November 1998 相似文献
10.
We present here a neutron reflectivity study of the influence of an alternative electric field on a supported phospholipid
double bilayer. We report for the first time a reproducible increase of the fluctuation amplitude leading to the complete
unbinding of the floating bilayer. Results are in good agreement with a semi-quantitative interpretation in terms of negative
electrostatic surface tension. 相似文献
11.
Inclusions embedded in lipid membranes undergo a mediated force, due to the tendency of the membrane to relax its excess of
elastic energy. In this paper we determine the exact shape of a two-dimensional vesicle hosting two different inclusions,
and we analyse how the inclusion conformation influences the mediated interaction. We find non-trivial equilibrium configurations
for the inclusions along the hosting membrane, and we derive the complete phase diagram of the mediated interaction. In particular,
we find a non-vanishing mediated force even when the distance between the inclusions is much greater than their size. Our
model can be applied to describe the mediated interactions of parallel, elongated inclusions embedded in three-dimensional
membranes.
Received 22 October 2001 and Received in final form 8 March 2002 相似文献
12.
Mader MA Vitkova V Abkarian M Viallat A Podgorski T 《The European physical journal. E, Soft matter》2006,19(4):389-397
The dynamics of giant lipid vesicles under shear flow is experimentally investigated. Consistent with previous theoretical
and numerical studies, two flow regimes are identified depending on the viscosity ratio between the interior and the exterior
of the vesicle, and its reduced volume or excess surface. At low viscosity ratios, a tank-treading motion of the membrane
takes place, the vesicle assuming a constant orientation with respect to the flow direction. At higher viscosity ratios, a
tumbling motion is observed in which the whole vesicle rotates with a periodically modulated velocity. When the shear rate
increases, this tumbling motion becomes increasingly sensitive to vesicle deformation due to the elongational component of
the flow and significant deviations from simpler models are observed. A good characterization of these various flow regimes
is essential for the validation of analytical and numerical models, and to relate microscopic dynamics to macroscopic rheology
of suspensions of deformable particles, such as blood. 相似文献
13.
We studied the formation of actin scaffolds in giant vesicles of dimyristoylphosphatidylcholine (DMPC). Polymerization of
actin was induced at low ionic strength through ionophore-mediated influx of Mg2+ (2 mM). The spatial organization of the filamentous actin was visualized by confocal and epifluorescence microscopy as a
function of the filaments length and membrane composition, by including various amounts of cholesterol or lipids with neutral
and positively charged polyethyleneglycol headgroups (PEG lipopolymers). In vesicles of pure DMPC, the newly polymerized actin
adsorbs to the membrane and forms a thin shell. In the presence of 2.5 mol% lipopolymers or of cholesterol at a molar fraction
x = 0.37, formation of a thin adsorbed film is impeded. A fuzzy cortex is predominantly formed in vesicles of diameter d smaller than the filament persistence length ( d ⩽ 15μm) while for larger vesicles a homogeneous network formation is favoured in the bulk of the vesicle. The fuzzy-cortex
formation is interpreted as a consequence of the reduction of the bending energy if the actin filaments accumulate close to
the vesicle wall.
Received: 17 January 2002 / Accepted: 21 March 2003 / Published online: 24 April 2003
RID="a"
ID="a"e-mail: Laurent_Limozin@ph.tum.de 相似文献
14.
15.
O. Dhez S. König D. Roux F. Nallet O. Diat 《The European physical journal. E, Soft matter》2000,3(4):377-388
A lyotropic system, consisting of a lecithin (DMPC) and a non-ionic surfactant (C12E5) in water was studied. The system exhibits a lamellar-to-nematic phase transition. The nematic phase appears as the temperature
is decreased and only exists in a very limited temperature and concentration range, for specific lipid-to-surfactant ratios.
While a lamellar phase is found at higher temperatures in both mixed and pure C12E5 systems, the transition to the nematic phase at lower temperatures coincides with a micellar phase in the pure C12E5 system. The transition appears to be driven by the strong temperature dependence of the surfactant film spontaneous curvature.
The structural properties of the lamellar phase close to the lamellar-to-nematic boundary have been studied by polarised light
microscopy and small-angle neutron and X-ray scattering experiments. The signature of a helical defect with Burgers vector
of magnitude 2 is apparent in our data, close to the lamellar-to-nematic phase transition. The proliferation of screw dislocations
in the lamellar phase might be a plausible mechanism for driving this transition.
Received 6 July 1999 and Received in final form 17 April 2000 相似文献
16.
Inside biological membranes, one of the fundamental functions of active proteins such as pumps is to generate some electrochemical
gradient across the membrane and then, to establish a new stationary state. The membrane electric potential generated by activity
modifies the stiffness constants of the membrane. A spontaneous curvature appears if the inner and outer Debye lengths are
different. The corresponding characteristic radius falls in the range from 0.08μm to 50μm. The bending elastic modulus is
always increased. This effect is only noticeable in the limit of large Debye length from 0.5μm to 0.09μm. For a Nernst potential
of 100mV and a Debye length of 0.2μ m, the bending modulus can reach 40kBT.
An erratum to this article is available at . 相似文献
17.
C.W. Maier A. Behrisch A. Kloboucek D.A. Simson R. Merkel 《The European physical journal. E, Soft matter》2001,6(4):273-276
We studied biomembrane adhesion using the micropipet aspiration technique. Adhesion was caused by contact site A, a laterally
mobile and highly specific cell adhesion molecule from Dictyostelium discoideum, reconstituted in lipid vesicles of DOPC (L-α-dioleoylphosphatidylcholine) with an addition of 5 mol % DOPE-PEG2000 (1,2-diacyl-sn-glycero-3-phosphatidylethanolamine-N-[poly(ethyleneglycol) 2000]). The “fuzzy” membrane mimics the cellular
plasma membrane including the glycocalyx. We found adhesion and subsequent receptor migration into the contact zone. Using
membrane tension jumps to probe the equation of state of the two-dimensional “gas” of bound receptor pairs within the contact
zone, we found strong, attractive lateral interactions.
Received 16 February 2001 相似文献
18.
R. Menes N. Grønbech-Jensen P.A. Pincus 《The European physical journal. E, Soft matter》2000,1(4):345-349
Using both theoretical modeling and computer simulations we study a model system for DNA interactions in the vicinity of charged
membranes. We focus on the polarization of the mobile charges in the membranes due to the nearby charged rods (DNA) and the
resulting screening of their fields and inter-rod interactions. We find, both within a Debye-Hückel model and in Brownian
dynamics simulations, that the confinement of the mobile charges to the surface leads to a qualitative reduction in their
ability to screen the charged rods to the degree that the fields and resulting interactions are not finite-ranged as in systems
including a bulk salt concentration, but rather decay algebraically and the screening effect is more like an effective increase
in the multipole moment of the charged rod.
Received 28 September 1999 相似文献
19.
Sabín J Prieto G Ruso JM Sarmiento F 《The European physical journal. E, Soft matter》2007,24(2):201-210
We present a study of the fractal dimension of clusters of large unilamellar vesicles (LUVs) formed by egg yolk phosphatidylcholine
(EYPC), dimyristoylphosphocholine (DMPC) and dipalmitoylphosphocholine (DPPC) induced by Ca2+ . Fractal dimensions were calculated by application of two methods, measuring the angular dependency of the light scattered
by the clusters and following the evolution of the cluster size. In all cases, the fractal dimensions fell in the range from
2.1 to 1.8, corresponding to two regimes: diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation
(RLCA). Whereas DMPC clusters showed a typical transition from the RLCA to the DLCA aggregation, EYPC exhibited an unusual
behaviour, since the aggregation was limited for a higher concentration than the critical aggregation concentration. The behaviour
of DPPC was intermediate, with a transition from the RLCA to the DLCA regimes with cluster sizes depending on Ca2+ concentration. Studies on the reversibility of the aggregates show that EYPC and DPPC clusters can be re-dispersed by dilution
with water. DMPC does not present reversibility. Reversibility is evidence of the existence of secondary minima in the DLVO
potential between two liposomes. To predict these secondary minima, a correction of the DLVO model was necessary taking into
account a repulsive force of hydration. 相似文献
20.
Equilibrium phase coexistence between two chemical species implies the equality of the chemical potentials and of the osmotic
pressures. We study this problem on a deformable membrane when one type of the molecules serves as anchor for polymeric chains
immersed in the surrounding medium (considered as a good solvent). We derive the general conditions for phase coexistence
when both the curvature of the membrane and the density field of the anchor molecule are free to adjust themselves. We show
that curvature favors phase segregation. Our model predicts that membranes decorated with polymeric chains exhibit new shape
bifurcations without equivalent in fixed density systems.
Received: 26 November 2002 / Accepted: 2 April 2003 / Published online: 12 May 2003
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ID="a"e-mail: nicolas@drfmc.ceng.cea.fr
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ID="b"e-mail: bfourcade@cea.fr 相似文献