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DissertationDOI

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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Citations
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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

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

Journal ArticleDOI
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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Journal ArticleDOI
TL;DR: A cell-dynamical-system (CDS) model of the microphase separation of block copolymers is described in detail and a partial-differential-equation (PDE) model is suggested that allows us to find a close relation between the blockCopolymer and spinodal decomposition problems.
Abstract: A cell-dynamical-system (CDS) model of the microphase separation of block copolymers is described in detail. The model suggests a partial-differential-equation (PDE) model that allows us to find a close relation between the block copolymer and spinodal decomposition problems. A detailed numerical study of the CDS model is given, which indicates that hydrodynamic effects are crucial for very late time-ordering processes. The strong segregation regime is studied analytically with the aid of an exactly solvable PDE model, which is suggested by the universality supported by the CDS simulations. The results obtained show that dimensional analysis gives the correct exponent for the block copolymer lamellar thickness.

210 citations


"Interplay Between Long-Range And Sh..." refers methods in this paper

  • ...It is tempting to use the “string method” to be discussed in the Chapter 5 in Part II, which is an efficient method to locate extremum as well as saddle points on the free energy landscape, or to adapt the cell dynamics approach by Bahiana and Oono (1990)....

    [...]

Journal Article

209 citations

Journal ArticleDOI
TL;DR: Cell adhesion is controlled by a complex interplay of short range (lock-and-key) forces mediated by cell surface receptors, a phalanx of (short and long range) nonspecific (generic) interactions, and last but not least membrane elasticity.
Abstract: Cell adhesion is controlled by a complex interplay of short range (lock-and-key) forces mediated by cell surface receptors, a phalanx of (short and long range) nonspecific (generic) interactions, and last but not least membrane elasticity. The physical basis of cell adhesion is explored by the design of simplified model systems, mimicking cell and tissue surfaces, enabling local measurements of cellular shape changes and adhesion forces by microinterferometry. Cell adhesion can be understood as first-order dewetting transition that results in the formation of adhesion plaques, such as focal adhesion sites of cells, which allow cell adhesion at astonishingly low receptor densities. The repeller molecules of the glycocalix play a key role for the control of the adhesion transition and the mechanical stability of the adhering cells by relaxing the strength of the binding forces. Stress fibers are postulated to be essential for the stabilization of adhesion domains against leverage through bending moments enforced by hydrodynamic shear forces.

193 citations


"Interplay Between Long-Range And Sh..." refers background or methods in this paper

  • ...Finally we point out that due to the barrier between the bound and the unbound state, even in flat geometries the adhesion process should be a first-order transition (Bruinsma and Sackmann, 2002; Weikl et al., 2002)....

    [...]

  • ..., 1996) and theoretical estimations (Bruinsma et al., 2000; Bruinsma and Sackmann, 2002) suggest that in the adhesion of cells or vesicles, the small contact adhesion zones have ligand-receptor bonds aggregated at much higher densities than the bulk average....

    [...]

  • ...Despite the complexity of these interactions, researchers have been successful in explaining many experimental observations from thermodynamic and physico-chemical analysis, and many features of cell adhesion can be qualitatively understood from basic physical principles (Bell, 1978; Bell et al., 1984; Torney et al., 1986; Coombs et al., 2004; Flyvbjerg et al., 1997; Zukerman and Bruinsma, 1995; Lipowsky, 1996; Bruinsma et al., 2000; Boulbitch et al., 2001; Bruinsma and Sackmann, 2002; Sackmann and Bruinsma, 2002; Sackmann and Goennenwein, 2006)....

    [...]

  • ...The whole process is likened to the wetting transition (Bruinsma and Sackmann, 2002) and phenomenological parameters like the surface tension, the spreading pressure, and the contact angle can be measured and related to underlying parameters, including the mechanical properties of the membrane and the molecular parameters of receptors (Bruinsma et al....

    [...]

  • ...We offer a systematic analysis of the dynamics of the first-order adhesion typical for cell and membrane adhesion mediated by specific receptors (Bruinsma et al., 2000; Bruinsma and Sackmann, 2002; Sackmann and Goennenwein, 2006)....

    [...]

Journal ArticleDOI
TL;DR: The results for this model system demonstrate that adhesion strength varies with the logarithm of the binding affinity, consistent with a prediction from the theoretical model by Dembo et al.

183 citations


"Interplay Between Long-Range And Sh..." refers background in this paper

  • ...In many experimental settings ligands and receptors are fixed on beads (Kuo and Lauffenburger, 1993; Eniola et al., 2003) or covalently linked (Lin et al....

    [...]

  • ..., 2004; Cuvelier and Nassoy, 2004), and substrate-supported monolayer and bilayer membranes (Sackmann, 1996; Tanaka and Sackmann, 2005) allow better characterization of the specific and non-specific interactions because of the absence of complicating factors such as chemical signaling and deformability of biological cells in vivo (Lawrence and Springer, 1991; Dustin et al., 1996; Finger et al., 1996; Kuo and Lauffenburger, 1993; Eniola et al., 2003)....

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Journal ArticleDOI
TL;DR: A theoretical analysis of the intermembrane interaction in the presence of mobile repeller molecules at a fixed chemical potential shows that the interaction potential indeed should have just such a double-well shape.
Abstract: We report on a study of a model bioadhesion system: giant vesicles in contact with a supported lipid bilayer. Embedded in both membranes are very low concentrations of homophilic recognition molecules (contact site A receptors) competing with higher concentrations of repeller molecules: polyethylene glycol (PEG) lipids. These repellers mimic the inhibiting effect of the cell glycocalyx on adhesion. The effective adhesive interaction between the two membranes is probed by interferometric analysis of thermal fluctuations. We find two competing states of adhesion: initial weak adhesion is followed by slower aggregation of the adhesion molecules into small, tightly bound clusters that coexist with the regions of weak adhesion. We interpret our results in terms of a double-well intermembrane potential, and we present a theoretical analysis of the intermembrane interaction in the presence of mobile repeller molecules at a fixed chemical potential that shows that the interaction potential indeed should have just such a double-well shape. At a fixed repeller concentration we recover a conventional purely repulsive potential. We discuss the implications of our findings in terms of a general amplification mechanism of the action of sparse adhesion molecules by a nonspecific double-well potential. We also discuss the important role of the Helfrich undulation force for the proposed scenario.

182 citations


"Interplay Between Long-Range And Sh..." refers background in this paper

  • ..., 1996) and theoretical estimations (Bruinsma et al., 2000; Bruinsma and Sackmann, 2002) suggest that in the adhesion of cells or vesicles, the small contact adhesion zones have ligand-receptor bonds aggregated at much higher densities than the bulk average....

    [...]

  • ...Despite the complexity of these interactions, researchers have been successful in explaining many experimental observations from thermodynamic and physico-chemical analysis, and many features of cell adhesion can be qualitatively understood from basic physical principles (Bell, 1978; Bell et al., 1984; Torney et al., 1986; Coombs et al., 2004; Flyvbjerg et al., 1997; Zukerman and Bruinsma, 1995; Lipowsky, 1996; Bruinsma et al., 2000; Boulbitch et al., 2001; Bruinsma and Sackmann, 2002; Sackmann and Bruinsma, 2002; Sackmann and Goennenwein, 2006)....

    [...]

  • ...The whole process is likened to the wetting transition (Bruinsma and Sackmann, 2002) and phenomenological parameters like the surface tension, the spreading pressure, and the contact angle can be measured and related to underlying parameters, including the mechanical properties of the membrane and the molecular parameters of receptors (Bruinsma et al., 2000; Simson et al., 1998; Boulbitch et al., 2001)....

    [...]

  • ...We offer a systematic analysis of the dynamics of the first-order adhesion typical for cell and membrane adhesion mediated by specific receptors (Bruinsma et al., 2000; Bruinsma and Sackmann, 2002; Sackmann and Goennenwein, 2006)....

    [...]

  • ...The separation ∆L is between 5 and 50 nm, depending on the size of the receptors (Bruinsma et al., 2000; Martin et al., 2006), and we take L0 = 5 nm....

    [...]