共查询到20条相似文献,搜索用时 393 毫秒
1.
The adhesion of fluid vesicles at chemically structured substrates is studied theoretically via Monte Carlo simulations. The
substrate surface is planar and repels the vesicle membrane apart from a single surface domain γ , which strongly attracts
this membrane. If the vesicle is larger than the attractive γ domain, the spreading of the vesicle onto the substrate is restricted
by the size of this surface domain. Once the contact line of the adhering vesicle has reached the boundaries of the γ domain,
further deflation of the vesicle leads to a regime of low membrane tension with pronounced shape fluctuations, which are now
governed by the bending rigidity. For a circular γ domain and a small bending rigidity, the membrane oscillates strongly around
an average spherical cap shape. If such a vesicle is deflated, the contact area increases or decreases with increasing osmotic
pressure, depending on the relative size of the vesicle and the circular γ domain. The lateral localization of the vesicle's
center of mass by such a domain is optimal for a certain domain radius, which is found to be rather independent of adhesion
strength and bending rigidity. For vesicles adhering to stripe-shaped surface domains, the width of the contact area perpendicular
to the stripe varies nonmonotonically with the adhesion strength. 相似文献
2.
Development of self-reproducing vesicle systems is the first step for autopoietic cycles. We established a model self-reproducing vesicle system without the membrane molecule synthesis route. The model vesicle composed of cylinder- and inverse-cone-shaped lipids formed inclusion vesicles inside the mother vesicle, and the inclusion vesicles were then expelled by a temperature cycling. By changing the vesicle composition, the mother vesicles showed a budding-type self-reproduction pathway. A key concept of this system is the coupling of the main-chain transition and the shape of lipids. 相似文献
3.
R. Holzlöhner M. Schoen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):413-419
The fluctuation-induced interaction between two rod-like, rigid inclusions in a fluid vesicle is studied by means of canonical
ensemble Monte-Carlo simulations. The vesicle membrane is represented by a triangulated network of hard spheres. Five rigidly
connected hard spheres form rod-like inclusions that can leap between sites of the triangular network. Their effective interaction
potential is computed as a function of mutual distance and angle of the inclusions. On account of the hard-core potential
among these, the nature of the potential is purely entropic. Special precaution is taken to reduce lattice artifacts and the
influence of finite-size effects due to the spherical geometry. Our results show that the effective potential is attractive
and short-range compared with the rod length L. Its well depth is of the order of , where is the bending modulus.
Received 5 February 1999 and Received in final form 14 May 1999 相似文献
4.
B. Božič V. Heinrich S. Svetina B. Žekš 《The European physical journal. E, Soft matter》2001,6(1):91-98
Shapes of nearly cylindrical sections of axisymmetric phospholipid membranes are studied theoretically. Describing the shape
of such sections by their deviation from a reference cylinder, the well-established shape equation for axisymmetric bilayer
membranes is expanded in terms of this deviation, and it is then solved analytically. The phase diagram shows the resulting
stationary shapes as functions of system parameters and external conditions, i.e., the pressure difference across the membrane, the membrane tension, the difference between the tensions of the two monolayers,
and the axial force acting on the vesicle. The accuracy of the approximate analytical solution is demonstrated by comparison
with numerical results. The obtained analytical solution allows to extend the analysis to include shapes where numerical methods
have failed.
Received 27 September 2000 and Received in final form 26 March 2001 相似文献
5.
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
6.
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
7.
We present a model of bi-phasic vesicles in the limit of large surface tension. In this regime, the vesicle is completely
stretched and well described by two spherical caps with a fold, which concentrates the membrane stress. The conservation laws
and geometric constraints restrict the space of possible shapes to a pair of solutions labeled by a parameter
given by line tension/pressure. For a given value of
, the two solutions differ by the length of the interface between domains. For a critical value,
, the two vesicle shapes become identical and no connected solution exists above this critical value. This model sheds new
light on two proposed mechanisms (osmotic shocks and molecule absorption) to explain the budding and the fission in recent
experiments. 相似文献
8.
The density of the elastic energy of a deformed membrane in a liquid state is calculated. The thermodynamic equilibrium of
its different parts is taken into account. The shape equation of a closed membrane is deduced. The quantity which keeps its
value, when the variations of the energy of the system are calculated, is not the area of the deformed membrane, but its area
in the flat tension free state. Because of this, additional terms appear in the second variation around the stable state.
The case of a lipid bilayer and its fluctuations is examined for both free and blocked exchange of molecules between the monolayers,
comprising the bilayer.
Received 4 February 2002 / Received in final form 15 April 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: bivas@issp.bas.bg 相似文献
9.
We develop a theory for shrinkage dynamics of a vesicle interacting with surfactant molecules. A stepwise shrinkage is formulated
in such a way that it consists of two processes. One is a nucleation process of a pore under increasing of the membrane tension.
The other is a closure process of the pore due to the line tension of the pore edge after leakage of the inner fluid. We carry
out numerical simulations and show that the results agree with experiments semi-quantitatively. An analytical study is also
carried out to understand the periodic shrinkage. 相似文献
10.
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
11.
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
12.
R. Dimova U. Seifert B. Pouligny S. Förster H.-G. Döbereiner 《The European physical journal. E, Soft matter》2002,7(3):241-250
Giant vesicles prepared from the diblock copolymer polybutadien-b-polyethyleneoxide (PB-PEO) exhibit a shear surface viscosity,
which is about 500 times higher than those found in common phospholipid bilayers. Our result constitutes the first direct
measurement of the shear surface viscosity of such polymersomes. At the same time, we measure bending and stretching elastic
constants, which fall in the range of values typical for lipid membranes. Pulling out a tether from an immobilized polymersome
and following its relaxation back to the vesicle body provides an estimate of the viscous coupling between the two monolayers
composing the polymer membrane. The detected intermonolayer friction is about an order of magnitude higher than the characteristic
one for phospholipid membranes. Polymersomes are tough vesicles with a high lysis tension. This, together with their robust
rheological properties, makes them interesting candidates for a number of technological applications.
Received 2 March 2001 and Received in final form 15 February 2002 相似文献
13.
H. Koibuchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):321-330
Two types of surface models have been investigated by Monte Carlo simulations on triangulated spheres with compartmentalized
domains. Both models are found to undergo a first-order collapsing transition and a first-order surface fluctuation transition.
The first model is a fluid surface one. The vertices can freely diffuse only inside the compartments, and they are prohibited
from the free diffusion over the surface due to the domain boundaries. The second is a skeleton model. The surface shape of
the skeleton model is maintained only by the domain boundaries, which are linear chains with rigid junctions. Therefore, we
can conclude that the first-order transitions occur independent of whether the shape of surface is mechanically maintained
by the skeleton (=the domain boundary) or by the surface itself. 相似文献
14.
15.
N. S. Gov 《The European physical journal. E, Soft matter》2009,29(3):337-344
The distribution of widths of axons was recently investigated, and was found to have a distinct peak at an optimized value.
The optimized axon width at the peak may arise from the conflicting demands of minimizing energy consumption and assuring
signal transmission reliability. The distribution around this optimized value is found to have a distinct non-Gaussian shape,
with an exponential “tail”. We propose here a mechanical model whereby this distribution arises from the interplay between
the elastic energy of the membrane surrounding the axon core, the osmotic pressure induced by the neurofilaments inside the
axon bulk, and active processes that remodel the microtubules and neurofilaments inside the axon. The axon’s radius of curvature
can be determined by the cell’s control of the osmotic pressure difference across the membrane, the membrane tension or by
changing the composition of the different components of the membrane. We find that the osmotic pressure, determined by the
neurofilaments, seems to be the dominant control parameter. 相似文献
16.
P. Fromherz V. Kiessling K. Kottig G. Zeck 《Applied Physics A: Materials Science & Processing》1999,69(5):571-576
Lipid bilayers on silicon may become the matrix of future bioelectronic devices if the junction is sufficiently insulating.
We touched the open gate of a field-effect transistor with a preformed giant lipid vesicle and bound the membrane by means
of polyelectrolyte interaction. The sheet resistance along the junction was 100 GΩ and the membrane resistance was above 100 GΩ
at a contact area of 1000 μm2. The bilayer was fluid and smoothly followed the surface profile of the chip. The compound lipid–silicon structure is suitable
to couple semiconductor and electroactive proteins.
Received: 12 August 1999 / Accepted: 16 August 1999 / Published online: 6 October 1999 相似文献
17.
We analyze the problem of vesicle migration in haptotaxis (a motion directed by an adhesion gradient), though most of the
reasoning applies to chemotaxis as well as to a variety of driving forces. A brief account has been published on this topic
[#!Cantat99a!#]. We present an extensive analysis of this problem and provide a basic discussion of most of the relevant processes
of migration. The problem allows for an arbitrary shape evolution which is compatible with the full hydrodynamical flow in
the Stokes limit. The problem is solved within the boundary integral formulation based on the Oseen tensor. For the sake of
simplicity we confine ourselves to 2D flows in the numerical analysis. There are basically two regimes (i) the tense regime
where the vesicle behaves as a “droplet” with an effective contact angle. In that case the migration velocity is given by
the Stokes law. (ii) The flask regime where the vesicle has a significant (on the scale of the vesicle size) contact curvature.
In that case we obtain a new migration law which substantially differs from the Stokes law. We develop general arguments in
order to extract analytical laws of migration. These are in good agreement with the full numerical analysis. Finally we mention
several important future issues and open questions.
Received 24 June 2002 and Received in final form 4 February 2003 Published online: 16 April 2003
RID="a"
ID="a"e-mail: isabelle.cantat@univ-rennes1.fr 相似文献
18.
The classical treatment of quasi-spherical vesicle undulations has, in the present work, been reviewed and extended to systems,
which are affected by a gravitational field caused by a density difference across the membrane. The effects have been studied
by the use of perturbation theory leading to corrections to the mean shape and the fluctuation correlation matrix. These corrections
have been included in an analytical expression for the flicker spectrum to probe how the experimentally accessible spectrum
changes with gravity. The results are represented in terms of the gravitational parameter, g
0 = ΔρgR
4/κ. The contributions from gravity are in most experimental situations small and thus negligible, but for values of g0 above a certain limit, the perturbational corrections must be included. Expressions for the relative error on the flicker
spectrum have been worked out, so that it is possible to define the regime where gravity is negligible. An upper limit of
g0 has also been identified, where the error in all modes of the flicker spectrum is significant due to distortion of the mean
shape.
Received 9 July 2002 and Received in final form 15 November 2002
RID="a"
ID="a"e-mail: jonas@kemi.dtu.dk
RID="b"
ID="b"e-mail: ipsen@memphys.sdu.dk 相似文献
19.
20.
Finken R Lamura A Seifert U Gompper G 《The European physical journal. E, Soft matter》2008,27(3):309-321
The stochastic motion of a two-dimensional vesicle in linear shear flow is studied at finite temperature. In the limit of
small deformations from a circle, Langevin-type equations of motion are derived, which are highly nonlinear due to the constraint
of constant perimeter length. These equations are solved in the low-temperature limit and using a mean-field approach, in
which the length constraint is satisfied only on average. The constraint imposes non-trivial correlations between the lowest
deformation modes at low temperature. We also simulate a vesicle in a hydrodynamic solvent by using the multi-particle collision
dynamics technique, both in the quasi-circular regime and for larger deformations, and compare the stationary deformation
correlation functions and the time autocorrelation functions with theoretical predictions. Good agreement between theory and
simulations is obtained. 相似文献