Hiroshi Noguchi

The dynamics of fluid vesicles and red blood cells (RBCs) in cylindrical capillary flow is studied by using a three-dimensional mesoscopic simulation approach. As flow velocity increases, a model RBC is found to transit from a nonaxisymmetric discocyteto an axisymmetric parachute shape (coaxial with the flow axis), while a fluid vesicle is found to transit from a discocyte to a prolate ellipsoid. Both shape transitions reduce the flow resistance. The critical velocities of the shape transitions

The effect of membrane viscosity on the dynamics of vesicles in shear flow is studied. We present a new simulation technique, which combines three-dimensional multiparticle collision dynamics for the solvent with a dynamically triangulated membrane model. Vesicles are found to transit from steady tank treading to unsteady tumbling motion with increasing membrane viscosity. Depending on the reduced volume and membrane viscosity, shear can induce both discocyte-to-prolate and prolate-to-discocyte

We studied the vesicles of amphiphilic molecules using a Brownian dynamics simulation. An amphiphilic molecule is modeled as the rigid rod, and the hydrophobic interaction is mimicked by the local density potential of the hydrophobic particles. The amphiphilic molecules self-assemble into vesicles with bilayer structure. The vesicles are in fluid phase, and we calculated the lateral diffusion constant and the rate of the flip-flop motion of molecules in vesicles. The self-assembly kinetics into

The dynamical behavior of vesicles is investigated in simple shear flow. A simulation technique is presented that combines a three-dimensional particle-based mesoscopic model (multiparticle collision dynamics) for the solvent with a dynamically triangulated surface model for the membrane. In this model, thermal fluctuations of the solvent and of the membrane are consistently taken into account. The membrane viscosity can be varied by changing the bond-flip rate of the dynamically triangulated su

We studied the thermodynamics in a single homopolymer chain using a multicanonical Monte Carlo simulation. A polymer chain that exhibits an elongated coil state in a good solvent, or at high temperatures, collapses into a condensed state, i.e., coil–globule transition. For flexible polymer chains, as the temperature decreases, the coil state changes into a liquidlike spherical globule, and this liquid state then changes into a solidlike spherical globule; these are similar to the transitions bet

We studied the fusion dynamics of vesicles using a Brownian dynamics simulation. Amphiphilic molecules spontaneously form vesicles with a bilayer structure. Two vesicles come into contact and form a stalk intermediate, in which a necklike structure only connects the outer monolayers, as predicted by the stalk hypothesis. We have found a new pathway of pore opening from stalks at high temperature: the elliptic stalk bends and contact between the ends of the arc-shaped stalk leads to pore opening.

The dynamics of fluid vesicles in simple shear flow is studied using mesoscale simulations of dynamically triangulated surfaces, as well as a theoretical approach based on two variables: a shape parameter and the inclination angle, which has no adjustable parameters. We show that, between the well-known tank-treading and tumbling states, a new "swinging" state can appear. We predict the dynamic phase diagram as a function of the shear rate, the viscosities of the membrane and the internal fluid,

Penicillin-binding proteins in Pseudomonas aeruginosa were compared with those of Escherichia coli. These in P. aeruginosa were found exclusively in the cytoplasmic membrane fraction (fraction soluble in sodium N-lauroyl sarcosinate). Sodium dodecyl sulfate/acrylamide gel electrophoresis of the proteins bound to [14C]penicillin G resulted in the separation of six major bands and several minor bands. The proteins in these bands are referred to as proteins 1A, 1B, 2, 3, 4 and 5 in order of increas

The viscosity and self-diffusion constant of particle-based mesoscale hydrodynamic methods, multiparticle collision dynamics (MPC), and dissipative particle dynamics, are investigated, both with and without angular-momentum conservation. Analytical results are derived for fluids with an ideal-gas equation of state and a finite-time-step dynamics, and compared with simulation data. In particular, the viscosity is derived in a general form for all variants of the MPC method. In general, very good

A meshless particle-based membrane model is proposed. The particles possess no internal degree of freedom and interact via a potential, which has three different contributions: a short-range repulsive pair potential, an attractive multibody potential, and a curvature potential based on the moving least-squares method. Brownian dynamics simulations are employed to demonstrate that the particles self-assemble into a membrane and to study equilibrium properties, such as bending rigidity, surface te

The dynamics of membranes is studied on the basis of a particle-based meshless surface model, which was introduced earlier [Phys. Rev. E 73, 021903 (2006)]. The model describes fluid membranes with bending energy and-in the case of membranes with boundaries-line tension. The effects of hydrodynamic interactions are investigated by comparing Brownian dynamics with a particle-based mesoscale solvent simulation (multiparticle collision dynamics). Particles self-assemble into vesicles via disk-shape

In living cells, membrane morphology is regulated by various proteins. Many membrane reshaping proteins contain a Bin/Amphiphysin/Rvs (BAR) domain, which consists of a banana-shaped rod. The BAR domain bends the biomembrane along the rod axis and the features of this anisotropic bending have recently been studied. Here, we report on the role of the BAR protein rods in inducing membrane tubulation, using large-scale coarse-grained simulations. We reveal that a small spontaneous side curvature per