Interplay Between Long-Range And Short-Range Interactions In Polymer Self-Assembly And Cell Adhesion
01 Jan 2008-
TL;DR: In this paper, reversible gelation of associating polymers and ligand-receptor interactions in membrane adhesion was studied, and the energy barrier of the adhesion as a result of membrane bending deformations and the double-well adhesion potential was calculated.
Abstract: Interplay between long-range and short-range interactions is a common theme in soft and biological matter, which results in complicated self-assembly behaviors. We study two examples of this interplay: reversible gelation of associating polymers and ligand-receptor interactions in membrane adhesion. In associating polymer solutions, the competition between the conformation flexibility of polymer chains and the enthalpic monomer interactions results in phase-separated micro-structures at the mesoscopic scale; both gelation and the microphase order-disorder transition are manifestations of this self-assembly. We further establish that reversible gelation is similar to the glass transition: both are characterized by ergodicity breaking, aperiodic micro-structures, and non-equilibrium relaxations over a finite temperature range. In the study of ligand-receptor interactions between surfaces, we emphasize the interplay between specific ligand-receptor binding, and generic physical interactions. We find that both the finite spatial extension of receptors and their mobilities affect their binding affinity. As a special case of the interplay between receptor binding and generic interactions, we study the dynamics of membrane adhesion that is mediated by receptor binding but fulfilled through membrane deformations. We calculate the energy barrier of the adhesion as a result of membrane bending deformations and the double-well adhesion potential, and analyze the different scenarios according to the shape of the adhesion potential by scaling arguments.
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01 Mar 1996
TL;DR: In this paper, a mean-field phase diagram for conformationally symmetric diblock melts using the standard Gaussian polymer model is presented, which traverses the weak- to strong-segregation regimes, is free of traditional approximations.
Abstract: A mean-field phase diagram for conformationally symmetric diblock melts using the standard Gaussian polymer model is presented. Our calculation, which traverses the weak- to strong-segregation regimes, is free of traditional approximations. Regions of stability are determined for disordered (DIS) melts and for ordered structures including lamellae (L), hexagonally packed cylinders (H), body-centered cubic spheres (QIm3m), close-packed spheres (CPS), and the bicontinuous cubic network with Ia3d symmetry (QIa3d). The CPS phase exists in narrow regions along the order−disorder transition for χN ≥ 17.67. Results suggest that the QIa3d phase is not stable above χN ∼ 60. Along the L/QIa3d phase boundaries, a hexagonally perforated lamellar (HPL) phase is found to be nearly stable. Our results for the bicontinuous Pn3m cubic (QPn3m) phase, known as the OBDD, indicate that it is an unstable structure in diblock melts. Earlier approximation schemes used to examine mean-field behavior are reviewed, and compa...
1,256 citations
554 citations
Posted Content•
TL;DR: It is shown that a system with competing interactions on different length scales, relevant to the formation of stripes in doped Mott insulators, undergoes a self-generated glass transition which is caused by the frustrated nature of the interactions and not related to the presence of quenched disorder.
Abstract: Using our previous results for the configurational entropy of a stripe glass as well as a variational result for the bare surface tension of entropic droplets we show that there is no disagreement between the numerical simulations of Grousson et al. and our theory. The claim that our theory disagrees with numerical simulations is based on the assumption that the surface tension is independent of the frustration parameter Q of the model. However, we show in this Reply that it varies strongly with Q and that the resulting Q-dependence of the kinetic fragility agrees with the one obtained by Grousson et al. We believe that this answers the questions raised in the Comment by Grousson et al.
127 citations
TL;DR: In this paper, eine Einfiihrung in einige aktuelle Forschungsaspekte aus dem Bereich der Biophysik zu geben is discussed.
Abstract: Das Ziel dieses Buches ist es, eine Einfiihrung in einige aktuelle Forschungsaspekte aus dem Bereich der Biophysik zu geben. Der Inhalt des Buches umfaBt folgende Teilgebiete: den Einsatz der Mikrolithographie zur DNA-Trennung, die Modellierung der Faltung, Struktur und Dynamik von Proteinen, neuere theoretische Ansátze zur Proteinfaltung, die Physik der Organellen, Mechanismen molekularer Motorén, die Dynamik von Mikrotubuli, Formübergange und Fluktuationen von Membránén, Vesikeln und Zellen, die Biophysik des Gehirns und seiner Neuronen, weiterhin werden die sensorische Signalverarbeitung, molekulare evolutionsbiologische Strategien und potentielle Anwendungen, die Musterbildung beim Wachstum bakterieller Kolonien und Evolutionsmodelle erotteti. Das Buch, das aus einer Sommerschule und einem Workshop hervorgegangen ist, richtet sich an fortgeschrittene Studenten und an Doktoranden der Physik, Chemie und Biologie (z.T. sind mathematische Kenntnisse erforderlich!), aber auch an Forscher, die sich mit biophysikalischen Fragestellungen beschaftigen und einen aktuellen Einstieg in die angesprochenen modernen Forschungsfelder der Biophysik suchen. Die Artikel sind
18 citations
Journal Article•
TL;DR: The selectivity of cell-cell and cell-tissue adhesion is determined by specific short range forces between cell surface proteins, which function as constraint reaction spaces facilitating the local assembly of actin stress fibers and control cell signalling processes.
Abstract: The selectivity of cell-cell and cell-tissue adhesion is determined by specific short range forces between cell surface proteins. Long range entropic interfacial forces (mediated by repeller molecules and membrane undulations) and adhesion-induced elastic stresses in the cell envelope serve the fine control of the strength and duration of adhesion. The initial step of cell adhesion exhibits typical features of a first order wetting transition resulting in the formation of tight adhesion domains by lateral phase separation of receptors. External lift forces can cause shrinking and unbinding of adhesion sites if the receptors are immobile but induce domain growth if they are mobile. Strong adhesion domains (resisting nano-Newton forces) can form by commitment of some 10,000 receptors enabling cells to control adhesion strength rapidly by varying the receptor and repeller densities on cell surfaces through endocytosis and exocytosis. The adhesion domains can function as constraint reaction spaces facilitating the local assembly of actin stress fibers and control cell signalling processes as shown for the activation of immunological responses by immunological synapses.
12 citations
References
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TL;DR: It is demonstrated how the strength and distance of the minimal interaction can be controlled by the proper choice of polymer chain length, surface coverage, and type of functional end-group.
Abstract: We have investigated the interactions between single-walled carbon nanotubes, coated with polymer chains end-grafted to the tubes, and planar surfaces. By proper functionalization of the grafted polymers' free ends, we show how to obtain an attractive interaction that can be used to immobilize the tube at a desired distance from the surface. We demonstrate how the strength and distance of the minimal interaction can be controlled by the proper choice of polymer chain length, surface coverage, and type of functional end-group.
32 citations
"Interplay Between Long-Range And Sh..." refers background in this paper
..., 2006; Moore and Kuhl, 2006; Moreira and Marques, 2004; Sain and Wortis, 2004), and suggests a new route to controlling the interactions between surfaces typically achieved by generic physical interactions (Israelachvili, 1992; Hiddessen et al., 2000; Carignano and Szleifer, 2003; Nap and Szleifer, 2005)....
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TL;DR: Simulations of receptor binding confirm the high efficiency of receptor targeting by bidisperse polymer layers, which is achieved by means of larger compressibility and higher capability of the ligands to reach out compared to the corresponding monodisperse layers.
Abstract: Using Monte Carlo simulations we study the influence of ligand architecture (valence, branching length) and structure (polydispersity) of a flat protective polymer layer on the accessibility of its functional groups and efficiency of receptor targeting. Two types of receptor surfaces were considered: the surface homogeneously covered with receptors and the surface containing a finite number of receptor sites. We found that multivalent ligands provide a larger density of targeting groups on the periphery of the layer compared to monovalent ligands for the same overall number of targeting groups per polymer layer. Because of their cooperativity in binding, multivalent ligands were also considerably more efficient in binding to both types of receptor surfaces. With an increase of ligand valence the number of functional groups attached to receptors noticeably increases. Short-branched divalent ligands show an especially high cooperativity in binding to closely packed receptors. However, in the case of immobile receptors separated by a finite distance from each other, the average distance between the functional groups belonging to the same short divalent ligand is too small to reach different receptors simultaneously and the receptor binding is less efficient than in the monovalent ligand case. Using a bidisperse protective polymer layer formed by short nonfunctional polymers and long functionalized polymers considerably increases the fraction of functional groups on the periphery of the layer. Simulations of receptor binding confirm the high efficiency of receptor targeting by bidisperse polymer layers, which is achieved by means of larger compressibility and higher capability of the ligands to reach out compared to the corresponding monodisperse layers. The concepts of multivalent ligands and a bidisperse protective polymer layer each have their own advantages which can be combined for an enhanced targeting effect.
31 citations
TL;DR: In this article, the disorder-to-order transition in polystyrene-block polyisoprene copolymer was studied after it was thermally quenched from the disordered state to the ordered state.
Abstract: The kinetics of the disorder-to-order transition in a polystyrene-block-polyisoprene copolymer was studied after it was thermally quenched from the disordered state to the ordered state. The ordered state consists of cylinders arranged on a hexagonal lattice. This state has liquid crystalline symmetry with liquidlike disorder along the cylinders axis and crystalline order in the hexagonal plane. We monitor the kinetics of microstructure formation in the liquid and crystalline directions by a combination of time-resolved depolarized light scattering and small-angle X-ray scattering experiments. At small quench depths, microstructure formation along the liquid and crystalline directions is strongly correlated during all stages of the disorder-to-order transition. We demonstrate that this is expected when microstructure formation occurs by classical nucleation and growth. At large quench depths, however, microstructure formation along the liquid and crystalline directions is not correlated. The growth of cry...
29 citations
TL;DR: In this article, the authors considered a melt of cyclic polymers (n monomers per chain) containing a small volume fraction ϕ of open cycles (P monomer per chain, with P max P1/2/N,(1/N) exp(const/P).
Abstract: We consider a melt of cyclic polymers (N monomers per chain) containing a small volume fraction ϕ of open cycles (P monomers per chain, with P max P1/2/N,(1/N) exp(const/P). Our study is restricted to N-rings that are small enough for their conformations to be Gaussian.
27 citations
"Interplay Between Long-Range And Sh..." refers background in this paper
...The open ends of polymers can also be closed to form rings, then these rings can interconnect with each other to form the so-called “Olympic” gel (Raphaël et al., 1997)....
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...The open ends of polymers can also be closed to form rings, then these rings can interconnect with each other to form the so-called “Olympic” gel (Raphaël et al., 1997)....
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TL;DR: The results suggest that the thermodynamically disordered phase of such a minimal model poorly caricatures the slow dynamics of a liquid near its glass transition.
Abstract: We present simulation results for the dynamics of a schematic model based on the frustration-limited domain picture of glass-forming liquids. These results are compared with approximate theoretical predictions analogous to those commonly used for supercooled liquid dynamics. Although model relaxation times increase by several orders of magnitude in a non-Arrhenius manner as a microphase separation transition is approached, the slow relaxation is in many ways dissimilar to that of a liquid. In particular, structural relaxation is nearly exponential in time at each wave vector, indicating that the mode-coupling effects dominating liquid relaxation are comparatively weak within this model. Relaxation properties of the model are instead well reproduced by the simplest dynamical extension of a static Hartree approximation. This approach is qualitatively accurate even for temperatures at which the mode-coupling approximation predicts loss of ergodicity. These results suggest that the thermodynamically disordered phase of such a minimal model poorly caricatures the slow dynamics of a liquid near its glass transition.
27 citations
"Interplay Between Long-Range And Sh..." refers methods in this paper
...1 Glass transition Glass transitions in the Coulomb-frustrated-magnet model have been addressed by several groups in recent years (Nussinov et al., 1999; Grousson et al., 2001, 2002a,b; Schmalian and Wolynes, 2000; Westfahl et al., 2001; Geissler and Reichman, 2004; Nussinov, 2004; Wu et al., 2004)....
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