34 research outputs found
Hydrodynamic lift on bound vesicles
Bound vesicles subject to lateral forces such as arising from shear flow are
investigated theoretically by combining a lubrication analysis of the bound
part with a scaling approach to the global motion. A minor inclination of the
bound part leads to significant lift due to the additive effects of lateral and
tank-treading motions. With increasing shear rate, the vesicle unbinds from the
substrate at a critical value. Estimates are in agreement with recent
experimental data.Comment: 9 pages, one figur
Geometry of lipid vesicle adhesion
The adhesion of a lipid membrane vesicle to a fixed substrate is examined
from a geometrical point of view. This vesicle is described by the Helfrich
hamiltonian quadratic in mean curvature; it interacts by contact with the
substrate, with an interaction energy proportional to the area of contact. We
identify the constraints on the geometry at the boundary of the shared surface.
The result is interpreted in terms of the balance of the force normal to this
boundary. No assumptions are made either on the symmetry of the vesicle or on
that of the substrate. The strong bonding limit as well as the effect of
curvature asymmetry on the boundary are discussed.Comment: 7 pages, some major changes in sections III and IV, version published
in Physical Review
Fluctuation spectrum of fluid membranes coupled to an elastic meshwork: jump of the effective surface tension at the mesh size
We identify a class of composite membranes: fluid bilayers coupled to an
elastic meshwork, that are such that the meshwork's energy is a function
\textit{not} of the real microscopic membrane area ,
but of a \textit{smoothed} membrane's area , which corresponds to the
area of the membrane coarse-grained at the mesh size . We show that the
meshwork modifies the membrane tension both below and above the scale
, inducing a tension-jump . The
predictions of our model account for the fluctuation spectrum of red blood
cells membranes coupled to their cytoskeleton. Our results indicate that the
cytoskeleton might be under extensional stress, which would provide a means to
regulate available membrane area. We also predict an observable tension jump
for membranes decorated with polymer "brushes"
Bilayer bending rigidity of some synthetic lecithins
The curvature elastic modulus of fluid membranes of DMPC, DPPC, and DSPC in water was measured. From the equilibrium distribution of the thermal bending fluctuations of tubular vesicles we obtained values of 2.4, 2.0, and 1.8 × 10-12 erg, respectively, with errors of about 20 %. We also observed some deformations of the fluctuating tubes such as sharp knee-like bends and pronounced short-waved wriggles which apparent elastic energies seem too high for thermal excitation.Nous avons mesuré le module d'élasticité de courbure des membranes fluides de DMPC, DPPC et DSPC dans l'eau. De la distribution d'équilibre des fluctuations thermiques de flexion de vésicules tubulaires, nous avons obtenu les valeurs de 2,4,2,0 et 1,8 x 10-12 erg avec une erreur d'environ 20 %. Nous avons également observé quelques déformations des tubules fluctuantes telles que des « coudes » bien marqués et des ondulations prononcées de courtes longueurs d'onde dont l'énergie élastique fictive nous a paru trop grande pour être excités thermiquement
Giant membranes of swollen phosphatidylethanolamines and glycolipids
The swelling of phosphatidylethanolamines and biological glycolipids is studied by phase contrast microscopy. In their fluid phase the bilayers of all the lipids separate in water and, with one proven exception, in NaCl solutions. The very rare mutual adhesion of giant membranes which normally separate is apparently always induced by lateral tensions. Its average contact angles are larger than in the case of egg phosphatidylcholine but, as there, do not depend on tension within the one or two powers of ten covered by the observations. Certain cerebrosides form needles and fibres when the bilayers are in the solid phase
Measurement of membrane elasticity by micro-pipette aspiration
The classical micro-pipette aspiration technique, applied for measuring the membrane bending elasticity, is in the present work reviewed and extended to span the range of pipette aspiration pressures going through the flaccid (low pressures) to tense (high pressures) membrane regime. The quality of the conventional methods for analysing data is evaluated using numerically generated data and a new method for data analysis, based on thermodynamic analysis and detailed statistical mechanical modelling, is introduced. The analysis of the classical method, where the membrane bending modulus is obtained from micro-pipette aspiration data acquired in the low-pressure regime, reveals a significant correction from membrane stretching elasticity. The new description, which includes the full vesicle geometry and both the membrane bending and stretching elasticity, is used for the interpretation of micro-pipette aspiration experiments conducted on SOPC (stearoyl-oleoyl-phosphatidyl-choline) lipid vesicles in the fluid phase. The data analysis, which is extended by detailed image analysis and a fitting procedure based on Monte Carlo integration, gives an estimate of the bending modulus, that agrees with previously published results obtained by the use of shape fluctuation analysis of giant unilamellar vesicles. The obtained estimate of the area expansion modulus, is automatically corrected for contributions from residual thermal undulations and the equilibrium area of the vesicle is resolved