Showing papers by "Udo Seifert published in 1995"
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TL;DR: Considering the hydrodynamics of a bilayer membrane under tension, some of the qualitative behavior seen is reproduced and a value for the wavelength of the instability is found in terms of independently measured material parameters, in rough agreement with the experimental values.
Abstract: We give a simple theory for recent experiments of Bar-Ziv and Moses% Phys. Rev. Lett. {\bf73} (1994) 1392, in which tubular vesicles are excited using laser tweezers to a ``peristaltic'' state. Considering the hydrodynamics of a bilayer membrane under tension, we reproduce some of the qualitative behavior seen and find a value for the wavelength of the instability in terms of independently measured material parameters, in rough agreement with the experimental values.
108 citations
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TL;DR: In this paper, the Lagrange multiplier was used to enforce the area constraint in the case of quasi-spherical vesicles, and the validity of the conventional approach using an effective tension was assessed.
Abstract: Vesicles are closed surfaces of bilayer membranes. Their mean shapes and fluctuations are governed by the competition of curvature energy and geometrical constraints on the enclosed volume and total surface area. A scheme to calculate these fluctuations to lowest order in the ratio of temperature to bending rigidity is developed. It is shown that for fluctuations that break a symmetry of the mean shape the area constraint indeed acts like a tension whose value is given by the Lagrange multiplier used to enforce the area constraint in the first place. As a consequence, these fluctuations are also insensitive to the specific variants of the curvature model. For fluctuations that preserve the symmetry of the mean shape the role of the area constraint is more subtle. The low temperature expansion breaks down in the spherical limit where with the excess area another small parameter enters. By incorporating the area constraint in this limit exactly, the validity of the conventional approach using an effective tension for fluctuations of quasi-spherical vesicles can be assessed.
94 citations
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TL;DR: A method is exploited for calculating explicitly the stability of arbitrary axisymmetric shapes to map out in a numerically exact way both the stable phases and the metastability of the low-lying shape branches, allowing the full (shape) phase diagram and the full stability diagram to be constructed.
Abstract: The equilibrium shapes of fluid-phase phospholipid vesicles in an aqueous solution are controlled by bending elasticity. The regime of nonvesiculated shapes at reduced volume v\ensuremath{\ge}1/ \ensuremath{\surd}2 involves the interplay of five branches of distinct stationary shapes: pears, prolates, oblates, stomatocytes, plus a branch of nonaxisymmetric shapes with the symmetry ${\mathit{D}}_{2\mathit{h}}$. We exploit a method for calculating explicitly the stability of arbitrary axisymmetric shapes to map out in a numerically exact way both the stable phases and the metastability of the low-lying shape branches. To obtain additional required information about nonaxisymmetric shapes, we calculate these by numerical minimization of the curvature energy on a triangulated surface. Combining these two methods allows us to construct the full (shape) phase diagram and the full stability diagram in this region. We provide explicit results for values of the bending constants appropriate to stearoyl-oleoyl-phosphatidylcholine; generalization to other values is straightforward. (c) 1995 The American Physical Society
77 citations
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58 citations
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TL;DR: This paper aims to demonstrate the efforts towards in-situ applicability of EMMARM, the objective of which is to provide real-time information about concrete mechanical properties of E-modulus.
Abstract: Hans-Gunther Dobereiner,1,2,3 Evan Evans,2 Udo Seifert,3 and Michael Wortis1 1Physics Department, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 2Department of Physics, University of British Columbia, 6224 Agriculture Road, Vancouver, British Columbia, Canada V6T 2A6 3Max-Planck-Institut fur Kolloidund Grenzflachenforschung, Kantstrasse 55, 14513 Teltow-Seehof, Germany (Received 15 May 1995)
46 citations
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TL;DR: In this paper, the authors theoretically study the behavior of vesicles filled with a liquid of higher density than the surrounding medium, a technique frequently used in experiments, and show that in the presence of gravity, these vesicle sink to the bottom of the container, and eventually adhere even on nonattractive substrates.
Abstract: We theoretically study the behaviour of vesicles filled with a liquid of higher density than the surrounding medium, a technique frequently used in experiments. In the presence of gravity, these vesicles sink to the bottom of the container, and eventually adhere even on non-attractive substrates. The strong size dependence of the gravitational energy makes large parts of the phase diagram accessible to experiments even for small density differences. For relatively large volume, non-axisymmetric bound shapes are explicitly calculated and shown to be stable. Osmotic deflation of such a vesicle leads back to axisymmetric shapes and, finally, to a collapsed state of the vesicle.
45 citations
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TL;DR: In this paper, the behavior of vesicles filled with a liquid of higher density than the surrounding medium is studied, and it is shown that in the presence of gravity the vesicle sinks to the bottom of the container, and eventually adhere even on non-attractive substrates.
Abstract: We theoretically study the behavior of vesicles filled with a liquid of higher density than the surrounding medium, a technique frequently used in experiments. In the presence of gravity, these vesicles sink to the bottom of the container, and eventually adhere even on non - attractive substrates. The strong size-dependence of the gravitational energy makes large parts of the phase diagram accessible to experiments even for small density differences. For relatively large volume, non-axisymmetric bound shapes are explicitly calculated and shown to be stable. Osmotic deflation of such a vesicle leads back to axisymmetric shapes, and, finally, to a collapsed state of the vesicle.
2 citations
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TL;DR: In this paper, a hydrodynamic theory of fluid bilayers in interaction with the surrounding water was developed and the effect of the laser is to induce a sudden tension in the membrane.
Abstract: Recently Bar-Ziv and Moses discovered a dynamical shape transformation induced in cylindrical lipid bilayer vesicles by the action of laser tweezers. We develop a hydrodynamic theory of fluid bilayers in interaction with the surrounding water and argue that the effect of the laser is to induce a sudden tension in the membrane. We refine our previous analysis to account for the fact that the shape transformation is not uniform but propagates outward from the laser trap. Applying the marginal stability criterion to this situation gives us an improved prediction for the selected initial wavelength and a new prediction for the propagation velocity, both in rough agreement with the experimental values. For example, a tubule of initial radius 0.7\micron\ has a predicted initial sinusoidal perturbation in its diameter with wavelength 5.5\micron, as observed. The perturbation propagates as a front with the qualitatively correct front velocity a bit less than 100\micron/sec. In particular we show why this velocity is initially constant, as observed, and so much smaller than the natural scale set by the tension. We also predict that the front velocity should increase linearly with laser power. Finally we introduce an approximate hydrodynamic model applicable to the fully nonlinear regime. This model exhibits propagating fronts as well as fully-developed ``pearled" vesicles similar to those seen in the experiments.