The actin cytoskeleton drives many essential biological processes, from cell morphogenesis to motility. Assembly of functional networks requires control over the speed at which filaments grow. How this can be achieved high and variable levels soluble subunits found in cells is unclear. Here we reconstitute assembly mammalian, non-muscle physiological concentrations profilin-actin. We discover that under these conditions, filament growth limited by profilin dissociating end elongation becomes...

Elastic capsules, prepared from droplets or bubbles attached to a capillary (as in pendant drop tensiometer), can be deflated by suction through the capillary. We study this deflation and show that combined analysis of shape wrinkling characteristics enables us determine elastic properties situ. Shape contours are analyzed fitted using equations derived nonlinear membrane-shell theory give modulus, Poisson ratio stress distribution membrane. include wrinkles, which generically form upon...

Abstract Contractile rings are formed from cytoskeletal filaments during cell division. Ring formation is induced by specific crosslinkers, while contraction typically associated with motor protein activity. Here, we engineer DNA nanotubes and peptide-functionalized starPEG constructs as synthetic crosslinkers to mimic this process. The crosslinker induces bundling of ten hundred into closed micron-scale in a one-pot self-assembly process yielding several thousand per microliter. Molecular...

We investigate buckling of soft elastic capsules under negative pressure or for reduced capsule volume. Based on nonlinear shell theory and the assumption a hyperelastic membrane, shape equations axisymmetric initially spherical are derived solved numerically. A rich bifurcation behavior is found, which presented in terms diagrams. The energetically preferred stable configuration deduced from least-energy principle both prescribed volume pressure. find that buckled shapes favorable already...

The stability of a vortex glass phase with quasi-long-range positional order is examined for disordered layered superconductor. role topological defects investigated using scaling argument supplemented by variational calculation. results indicate that preserved some range parameters in the phase. regime given terms simple Lindemann-like criterion and consistent recent experiments.

We develop a theory for dislocation-mediated structural transitions in the vortex lattice which allows unified description of phase between three phases, elastic glass, amorphous and liquid, terms free-energy functional dislocation density. In presence point defects, existence critical endpoint first-order melting line at high magnetic fields, has been recently observed experimentally, is explained.

We theoretically study the cooperative behavior of cytoskeletal filaments in motility assays which immobilized motor proteins bind to substrate surfaces and actively pull them along these surfaces. Because mutual exclusion filaments, coupled dynamics heads, tails leads a nonequilibrium phase transition generalizes isotropic-nematic corresponding equilibrium system, hard-rod fluid. Langevin simulations show that activity enhances tendency for nematic ordering. develop quantitative theory...

We discuss the destruction of vortex lattice order in type-II superconductors by random point pinning and thermal fluctuations based on Lindemann criteria. The location melting line order-disorder transition, which marks topologically ordered Bragg glass phase is reason for second peak effect, calculated. focus a comparative discussion different versions criteria and, with regard to experiment, three classes superconductors---low-${T}_{c},$ anisotropic high-${T}_{c},$ layered high-${T}_{c}$...

We provide a C/C++ software for the shape analysis of deflated elastic capsules in pendant capsule geometry, which is based on an description material as quasi two-dimensional membrane using shell theory. Pendant elastometry provides new situ and non-contact method interfacial rheology that goes beyond determination Gibbs- or dilational modulus from area-dependent measurements surface tension drop tensiometry, can only give rough estimate properties they are purely liquid interface model....

We develop a theory for plastic vortex creep in topologically disordered (dislocated) solid phase type-II superconductors terms of driven thermally activated dislocation dynamics. Plastic barriers dislocations show power-law divergence at small driving currents j, U(pl)( j) approximately j(-&mgr;), with &mgr; = 1 single and 2/5 bundles. This implies suppression the rate transition from ordered ( 2/11) to dislocated glass can manifest itself as an observed increase apparent critical current...

Despite the long history of investigations polyelectrolyte multilayer formation on solid or liquid surfaces, important questions remain open concerning construction first set layers. These are generally deposited a anchoring layer different chemistry, influencing their and properties. We propose here an in-depth investigation NaPSS/PAH multilayers at air/water interface in absence chemically layer, profiting from surface activity NaPSS. To analyse mechanical properties layers, we combine...

Bundles of semiflexible polymers such as actin filaments are studied theoretically. The bundle formation is governed by attractive filament interactions mediated cross-linking sticker molecules. Using a combination analytical arguments and Monte Carlo simulations, it shown that the bundles parallel requires threshold concentration linkers which becomes independent number for large bundles. unbinding happens in single, discontinuous transition. We discuss behavior thickness at below In bound...

We study the adsorption of semiflexible polymers such as polyelectrolytes or DNA on planar and curved substrates, e.g., spheres washboard substrates via short-range potentials using extensive Monte-Carlo simulations, scaling arguments, analytical transfer matrix techniques. show that threshold stiff a substrate can be controlled by polymer stiffness: requires highest potential strength if persistence length matches range potential. On i.e., an adsorbing sphere surface, additionally curvature...

We study the buckling of elastic spherical shells under osmotic pressure with osmolyte concentration exterior solution as control parameter. compare our results for bifurcation behavior mechanical control, that is, an empty capsule interior. find striking differences states between and buckling. Mechanical always leads to fully collapsed opposite sides in contact, whereas uncollapsed a single finite dimple are generic control. For sufficiently large interior concentrations, is...

Liquid droplets, gas bubbles, and membrane vesicles which are in contact with chemically structured substrate surfaces can undergo morphological transitions or shape transformations. The considered here consist of two types surface domains, γ δ, attract repel the vesicles, respectively. For droplets on a striped domain, one has to distinguish fixed end caps from those freely moving caps. Both channels wetting transitions. strong adhesion regime vesicle shapes have constant mean curvature...

The persistence length of semiflexible polymers and one-dimensional fluid membranes is obtained from the renormalization their bending rigidity. renormalized rigidity calculated using an exact real-space functional group transformation based on a mapping to Heisenberg model. vanishes exponentially at large scales its asymptotic behaviour used define length. For polymers, our result agrees with tangent correlation functions. Our definition differs one commonly for membranes, which perturbative

Wetting morphologies on solid substrates, which may be chemically or topographically structured, are studied theoretically by variation of the free energy contains contributions from substrate surface, fluid–fluid interface and three-phase contact line. The first this leads to two equations—the classical Laplace equation a generalized line equation—which determine stationary wetting morphologies. From second we derive general spectral stability criterion for In order incorporate constraint...

We study the morphologies of single liquid droplets wetting a substrate in presence line tension three-phase contact line. On homogeneous substrate, leads to discontinuous unbinding droplet if its volume is decreased below critical value. For structured surface with circular domain, contrast gives rise depinning transitions from domain boundary as varied. calculate corresponding free energy bifurcation diagram analytically for axisymmetric shapes. Numerical minimization shows that contrasts...

The local stability of a cylindrical liquid channel or filament deposited on planar homogeneous substrate is studied in the framework an effective interface model including line tension three phase contact line. We discuss with respect to transversally symmetric and antisymmetric deformation modes compute diagram terms angle longitudinal wavelength these for different values tension. An increase always leads channels filaments. For large positive tension, behaviour pinned lines recovered. As...

The hydrolysis of adenosine triphosphate (ATP) during actin (de)polymerization consists two subprocesses, ATP cleavage and phosphate (${\mathrm{P}}_{\mathrm{i}}$) release, which involve three nucleotide states each protomer. A new theoretical model that explicitly incorporates these different subprocesses is introduced compared with recent experimental data for depolymerization. These can be explained by strongly cooperative followed ${\mathrm{P}}_{\mathrm{i}}$ release but are incompatible...

We investigate stall force and polymerization kinetics of rigid protofilaments in a microtubule or interacting filaments bundles under an external load the framework discrete growth model. introduce concecpt cycles to describe stochastic kinetics, which allows us derive exact expression for force. find that is independent ensemble geometry distribution. Furthermore, proportional number increases linearly with strength lateral filament interactions. These results are corroborated by...

We study the buckling instability of filaments or elastic rods in two spatial dimensions presence thermal fluctuations. present an analytical solution based on a renormalizationlike procedure where we integrate out short wavelength fluctuations order to obtain effective theory governing instability. calculate resulting shift critical force by fluctuation effects and average projected filament length parallel direction as function applied contour filament. find that, buckled state, lead...

Confinement effects on single semiflexible macromolecules are of central importance for a fundamental understanding cellular processes involving biomacromolecules. To analyze the influence confinement fluctuations we study individual actin filaments in straight and curved microchannels. We experimentally characterize segment distributions fluctuating microchannels as function channel width. Moreover, effect curvature filament is investigated. find quantitative agreement between experimental...