scholarly journals Fast Simulation of Lipid Vesicle Deformation Using Spherical Harmonic Approximation

2016 ◽  
Vol 21 (1) ◽  
pp. 40-64
Author(s):  
Michael Mikucki ◽  
Yongcheng Zhou
Keyword(s):  
Harmonic Functions ◽  
Degrees Of Freedom ◽  
Finite Difference Methods ◽  
Harmonic Approximation ◽  
Lipid Vesicles ◽  
Membrane Curvature ◽  
Lipid Vesicle ◽  
Nonlinear Conjugate Gradient Method ◽  
Surface Harmonic ◽  
Curvature Energy

AbstractLipid vesicles appear ubiquitously in biological systems. Understanding how the mechanical and intermolecular interactions deform vesicle membranes is a fundamental question in biophysics. In this article we develop a fast algorithm to compute the surface configurations of lipid vesicles by introducing surface harmonic functions to approximate themembrane surface. This parameterization allows an analytical computation of the membrane curvature energy and its gradient for the efficient minimization of the curvature energy using a nonlinear conjugate gradient method. Our approach drastically reduces the degrees of freedom for approximating the membrane surfaces compared to the previously developed finite element and finite difference methods. Vesicle deformations with a reduced volume larger than 0.65 can be well approximated by using as small as 49 surface harmonic functions. The method thus has a great potential to reduce the computational expense of tracking multiple vesicles which deform for their interaction with external fields.

Osmotically-induced tension and the binding of N-BAR protein to lipid vesicles

Soft Matter ◽  
2016 ◽  
Vol 12 (8) ◽  
pp. 2465-2472 ◽  
Author(s):  
Jaime B. Hutchison ◽  
Aruni P. K. K. Karunanayake Mudiyanselage ◽  
Robert M. Weis ◽  
Anthony D. Dinsmore
Keyword(s):  
Osmotic Stress ◽  
Binding Affinity ◽  
Lipid Vesicles ◽  
Membrane Curvature ◽  
Protein Domain ◽  
Curvature Sensing

The binding affinity of a curvature-sensing protein domain (N-BAR) is measured as a function of applied osmotic stress while the membrane curvature is nearly constant.

1⁄4 Car Model for Suspension Trim Corrector Performances Evaluation

2016 ◽  
Vol 823 ◽  
pp. 205-210
Author(s):  
Adrian Ioan Niculescu
Keyword(s):  
Contact Force ◽  
Harmonic Functions ◽  
Degrees Of Freedom ◽  
The Body ◽  
Vertical Acceleration ◽  
Vertical Movements ◽  
The Road ◽  
Quarter Car Model ◽  
Car Model ◽  
Quarter Car

The paper presents a complex quarter car model obtained with ADAMS software, View module, useful in the first stage of suspension dimensioning and optimization.The model is equipped with compression and rebound stopper buffer and suspension trim corrector.The proposed quarter car model with two degrees of freedom (wheel and body) performs all these goals allowing changing:Geometrical elementsPosition of equilibrium, depending on vehicle load;Trim correction;Elastic and dissipative characteristics of the suspension and tire;Suspension stroke;Road profile, assessed either by simple or summation of harmonic functions or reproducing real roadsBuffers (for stroke limitation) position and characteristics;The models developed provide information on:Vertical stability assessed by vertical movements of the body and the longitudinal and transversal stability evaluated based on adherence characterized by wheel ground contact force and frequency of soil detachment wheel.Comfort assessed on the basis of body vertical acceleration and collision forces to the stroke ends.The body-road clearanceThe trim corrector efficiencyAll above performances evaluated function the road unevenness, acceleration, deceleration, turning regime.The damping characteristic is defined by damping forces at different speed for each strokes respectively one for rebound and other for compression.The contact force road-wheel is defined based tire rigidity law.The stopper buffer forces on rebound and compression are defined based each specific rigidity characteristics.The road excitation is realized with a function generator.The software allow the model evolution visualisation in real time, also generating the diagrams of displacements, forces, accelerations, speeds, for each elements or for relative evolution between diverse elements.The simulation was realized for unloaded and fully loaded car using a road generated by a sum of harmonic functions presented in equation (8).The excitation covers the specific frequencies area, being under the body frequencies up to the wheel proper frequencies.The realized ¼ car model, have reached the goal to evaluate the suspension trim correction advantages.The simulations confirm the trim corrector increases the suspension performances, thus for the analyzed case the trim corrector increase simultaneous:Body-ground clearance (evaluated by body higher increasing) between 18.5÷55.1 %Body stability (evaluated by maximal body displacement) between 9.8÷11.4 %Body comfort (evaluated by maximal body acceleration) between 3.4÷35.5 %Adherence (evaluated by maximal and RMS wheel-groundcontact force variation) between 7.0÷12.1 %Body and axles protection (evaluated by buffer strike force) between 10.8÷38.2 %

Numerical simulation of incompressible flows within simple boundaries: accuracy

1971 ◽  
Vol 49 (1) ◽  
pp. 75-112 ◽  
Author(s):  
Steven A. Orszag
Keyword(s):  
Numerical Simulation ◽  
Finite Difference ◽  
Spectral Methods ◽  
Degrees Of Freedom ◽  
Incompressible Flows ◽  
Finite Difference Methods ◽  
Fourier Method ◽  
Passive Scalar ◽  
Mathematical Basis ◽  
Improved Accuracy

Galerkin (spectral) methods for numerical simulation of incompressible flows within simple boundaries are shown to possess many advantages over existing finite-difference methods. In this paper, the accuracy of Galerkin approximations obtained from truncated Fourier expansions is explored. Accuracy of simulation is tested empirically using a simple scalar-convection test problem and the Taylor–Green vortex-decay problem. It is demonstrated empirically that the Galerkin (Fourier) equations involving Np degrees of freedom, where p is the number of space dimensions, give simulations at least as accurate as finite-difference simulations involving (2N)p degrees of freedom. The theoretical basis for the improved accuracy of the Galerkin (Fourier) method is explained. In particular, the nature of aliasing errors is examined in detail. It is shown that ‘aliasing’ errors need not be errors at all, but that aliasing should be avoided in flow simulations. An eigenvalue analysis of schemes for simulation of passive scalar convection supplies the mathematical basis for the improved accuracy of the Galerkin (Fourier) method. A comparison is made of the computational efficiency of Galerkin and finite-difference simulations, and a survey is given of those problems where Galerkin methods are likely to be applied most usefully. We conclude that numerical simulation of many of the flows of current interest is done most efficiently and accurately using the spectral methods advocated here.

Membrane Curvature Induced by Sugar and Polymer Solutions

1997 ◽  
Vol 489 ◽  
Author(s):  
H.-G. Döbereiner ◽  
A. Lehmann ◽  
W. Goedel ◽  
O. Selchow ◽  
R. Lipowsky
Keyword(s):  
Polymer Solutions ◽  
Lipid Vesicles ◽  
Membrane Curvature ◽  
Elastic Membrane ◽  
Spontaneous Curvature ◽  
Membrane Asymmetry ◽  
Bending Modulus ◽  
Bending Elasticity ◽  
Cellular Organelles

AbstractWe monitor the effect of transversal membrane asymmetry on the morphology of giant uni-lamellar vesicles in sugar and polymer solutions. The shapes of fluid lipid vesicles are governed by the bending elasticity of their membrane which is characterized by the bending modulus and the spontaneous curvature of the bilayer. We present a recently developed technique for the measurement of the spontaneous curvature using quantitative phase contrast microscopy. Different mechanisms for elastic membrane asymmetry and the role of the bending energy concept for the morphology of cellular organelles are discussed.

Deformation and rupture of lipid vesicles in the strong shear flow generated by ultrasound-driven microbubbles

2008 ◽  
Vol 464 (2095) ◽  
pp. 1781-1800 ◽  
Author(s):  
Philippe Marmottant ◽  
Thierry Biben ◽  
Sascha Hilgenfeldt
Keyword(s):  
Shear Flow ◽  
Acoustic Streaming ◽  
Three Dimensional ◽  
Spherical Shape ◽  
Lipid Vesicles ◽  
Boundary Integral ◽  
Elastic Response ◽  
Lipid Vesicle ◽  
Strong Shear ◽  
Vesicle Rupture

Considering the elastic response of the membrane of a lipid vesicle (artificial cell) in an arbitrary three-dimensional shear flow, we derive analytical predictions of vesicle shape and membrane tension for vesicles close to a spherical shape. Large amplitude deviations from sphericity are described using boundary integral numerical simulations. Two possible modes of vesicle rupture are found and compared favourably with experiments: (i) for large enough shear rates the tension locally exceeds a rupture threshold and a pore opens at the waist of the vesicle and (ii) for large elongations the local tension becomes negative, leading to buckling and tip formation near a pole of the vesicle. We experimentally check these predictions in the case of strong acoustic streaming flow generated near ultrasound-driven microbubbles, such as those used in medical applications.

Filaments of surfactant protein A specifically interact with corrugated surfaces of phospholipid membranes

1999 ◽  
Vol 276 (4) ◽  
pp. L631-L641 ◽  
Author(s):  
Nades Palaniyar ◽  
Ross A. Ridsdale ◽  
Stephen A. Hearn ◽  
Yew Meng Heng ◽  
F. Peter Ottensmeyer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Protein A ◽  
Lipid Vesicles ◽  
Surfactant Protein ◽  
Uranyl Acetate ◽  
Lipid Vesicle ◽  
Transmission Electron

Pulmonary surfactant, a mixture of lipids and surfactant proteins (SPs), plays an important role in respiration and gas exchange. SP-A, the major SP, exists as an octadecamer that can self-associate to form elongated protein filaments in vitro. We have studied here the association of purified bovine SP-A with lipid vesicle bilayers in vitro with negative staining with uranyl acetate and transmission electron microscopy. Native bovine surfactant was also examined by transmission electron microscopy of thinly sectioned embedded material. Lipid vesicles made from dipalmitoylphosphatidylcholine and egg phosphatidylcholine (1:1 wt/wt) generally showed a smooth surface morphology, but some large vesicles showed a corrugated one. On the smooth-surfaced vesicles, SP-As primarily interacted in the form of separate octadecamers or as multidirectional protein networks. On the surfaces of the striated vesicles, SP-As primarily formed regularly spaced unidirectional filaments. The mean spacing between adjacent striations and between adjacent filaments was 49 nm. The striated surfaces were not essential for the formation of filaments but appeared to stabilize them. In native surfactant preparations, SP-A was detected in the dense layers. This latter arrangement of the lipid bilayer-associated SP-As supported the potential relevance of the in vitro structures to the in vivo situation.

scholarly journals Interaction of phospholipid vesicles with cultured mammalial cells. I. Characteristics of uptake.

1975 ◽  
Vol 67 (1) ◽  
pp. 38-48 ◽  
Author(s):  
L Huang ◽  
R E Pagano
Keyword(s):  
Chinese Hamster ◽  
Lipid Vesicles ◽  
Metabolic Inhibitors ◽  
Lipid Vesicle ◽  
Lipid Phase ◽  
Lipid Uptake ◽  
V79 Cells ◽  
Prolonged Incubation ◽  
Exogenous Lipid ◽  
Effects Of Ph

The interaction of monolayer cultures of Chinese hamster V79 cells with artificially generated, unilamellar lipid vesicles (approximately 500 A diameter) was examined. Vesicles prepared from a variety of natural and synthetic radiolabeled phosphatidyl cholines (lecithins) were incubated with V79 cells bathed in a simple balanced salt solution. After incubation, the cells were analyzed for exogenous lipid incorporation. Large quantities (approximately 10(8) molecules/cell/h) of lecithin became cell associated without affecting cell viability. The effects of pH, charged lipids, and the influence of the vesicle lipid phase transition on the uptake process were examined. Glutaraldehyde fixation of cells before vesicle treatment, or incubation in the presence of metabolic inhibitors, failed to reduce the lecithin uptake by more than 25-50%, suggesting that the lipid uptake is largely energy independent. Cells in sparse culture took up about ten times more lipid than dense cultures. Prolonged incubation (greater than 15 h) of sparse cell cultures with lecithin vesicles resulted in significant cell death while no deleterious effect was found in dense cultures, or with 1:1 lecithin/cholesterol vesicles. When vesicle-treated cells were homogenized and fractionated, about 20-30% of the exogenous lipid was found in the plasma membrane fraction, with the remainder being distributed into intracellular fractions. Electron microscope radioautography further demonstrated that most of the internalized lipid was present in the cytoplasm, with little in the nucleus. These results are discussed in terms of possible modification of cell behavior by lipid vesicle treatment.

scholarly journals X-ray scattering from unilamellar lipid vesicles

2005 ◽  
Vol 38 (1) ◽  
pp. 126-131 ◽  
Author(s):  
Michael R. Brzustowicz ◽  
Axel T. Brunger
Keyword(s):  
Form Factor ◽  
Lipid Bilayer ◽  
Electron Density ◽  
Lipid Vesicles ◽  
Lipid Vesicle ◽  
Asymmetric Structure ◽  
Bilayer Structure ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

An improved small-angle X-ray scattering (SAXS) method for determining asymmetric lipid bilayer structure in unilamellar vesicles is presented. From scattering theory, analytic expressions are derived for the bilayer form factor over flat and spherical geometries, assuming the lipid bilayer electron density to be composed of a series of Gaussian shells. This is in contrast to both classic diffraction and Guinier hard-shell SAXS methods which, respectively, are capable only of ascertaining symmetric bilayer structure and limited-resolution asymmetric structure. Using model fitting and direct calculation of the form factor, using only one equation, an asymmetric electron density profile of the lipid vesicle is obtained with high accuracy, as well as the average radius. The analysis suggests that the inner leaflet of a unilamellar lipid vesicle is `rougher' than the outer one.

scholarly journals Pulsatile lipid vesicles under osmotic stress

2016 ◽  
Author(s):  
Morgan Chabanon ◽  
James C.S. Ho ◽  
Bo Liedberg ◽  
Atul N. Parikh ◽  
Padmini Rangamani
Keyword(s):  
Osmotic Stress ◽  
Lipid Bilayers ◽  
Degrees Of Freedom ◽  
Lipid Vesicles ◽  
Thermal Fluctuations ◽  
Equilibrium Dynamics ◽  
Scaling Relationships ◽  
Rate Dependent ◽  
Quantitative Understanding ◽  
Bursting Events

AbstractThe response of lipid bilayers to osmotic stress is an important part of cellular function. Previously, in (Oglecka et al., 2014), we reported that cell-sized giant unilamellar vesicles (GUVs) exposed to hypotonic media, respond to the osmotic assault by undergoing a cyclical sequence of swelling and bursting events, coupled to the membrane’s compositional degrees of freedom. Here, we seek to deepen our quantitative understanding of the essential pulsatile behavior of GUVs under hypotonic conditions, by advancing a comprehensive theoretical model for vesicle dynamics. The model quantitatively captures our experimentally measured swell-burst parameters for single-component GUVs, and reveals that thermal fluctuations enable rate dependent pore nucleation, driving the dynamics of the swell-burst cycles. We further identify new scaling relationships between the pulsatile dynamics and GUV properties. Our findings provide a fundamental framework that has the potential to guide future investigations on the non-equilibrium dynamics of vesicles under osmotic stress.

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