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Dissertation•DOI•

Interplay Between Long-Range And Short-Range Interactions In Polymer Self-Assembly And Cell Adhesion

Cheng-Zhong Zhang
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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Unifying Weak- and Strong-Segregation Block Copolymer Theories

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Mark W. Matsen1, Frank S. Bates1•
University of Minnesota1
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

Journal Article•DOI•
The immunological synapse: A molecular machine controlling T cell activation

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Sunny Dzik
01 Jan 2000-Transfusion Medicine Reviews

554 citations

Posted Content•
Reply to Comment on "Stripe glasses: self generated randomness in a uniformly frustrated system"

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Joerg Schmalian1, Peter G. Wolynes2•
Iowa State University1, University of California, San Diego2
12 Jan 2001-arXiv: Disordered Systems and Neural Networks
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 Article•DOI•
Physics of Biological Systems, From Molecules to Species

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R. Winter
01 Jan 1999-Zeitschrift für Physikalische Chemie
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•
Cell Adhesion as Dynamic Interplay of Lock-and-Key, Generic and Elastic Forces(Physics of Non-Equilibrium Systems: Self-Organized Structures and Dynamics Far from Equilibrium)

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Erich Sackmann, Stefanie Goennenwein
14 Dec 2006-Progress of Theoretical Physics Supplement
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 Article•DOI•
Phase equilibria in solutions of associating telechelic polymers : rings vs reversible network

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Alexander N. Semenov, I. A. Nyrkova, Michael E. Cates
06 Nov 1995-Macromolecules
TL;DR: In this paper, a mean-field theory of phase equilibria in solutions of semi-lexible telechelic polymers is presented, and it is shown that with a nonzero probability of 3fold aggregation, infinite cluster formation always occurs as a first-order transition, implying an equilibrium between a gas of small rings and a network of finite density, mixed with rings.
Abstract: A mean-field theory of phase equilibria in solutions of semiflexible telechelic polymers is presented. All functional groups at the ends of telechelic chains are assumed to be associated in 2-fold and 3-fold aggregates. It is shown that with a nonzero probability of 3-fold aggregation, infinite cluster (reversible network) formation always occurs as a first-order transition, implying an equilibrium between a gas of small rings and a network of finite density, mixed with rings. The phase-separation region is narrow if the effective energy of a 3-fold cross-link is high enough, but it might be also very wide (implying a large ratio of network volume fraction to that of rings in coexisting phases) if the cross-links are favorable. In the latter case clusters of three telechelic chains (triplets) might become more favorable than rings ; more complex finite clusters are never important.

45 citations

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

  • ...Later on, Semenov, Rubinstein and co-workers (Semenov et al., 1995b; Semenov and Rubinstein, 1998a) studied a similar model, but with different assumptions on the infinite cluster in the gel phase....

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  • ...This system is the most widely studied model for reversible gelation (Tanaka and Matsuyama, 1989; Tanaka and Stockmayer, 1994; Ishida and Tanaka, 1997; Semenov et al., 1995a,b; Semenov and Rubinstein, 1998a,b)....

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Journal Article•DOI•
Nature of Disordered Micelles in Sphere-Forming Block Copolymer Melts

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Jiafang Wang, Zhen-Gang Wang, Yuliang Yang
10 Feb 2005-Macromolecules
TL;DR: In this paper, the authors studied the nature of disordered micelles in highly asymmetric, sphere-forming diblock copolymer melts using the self-consistent field theory.
Abstract: Taking a nucleation perspective, we study the nature of the disordered micelles in highly asymmetric, sphere-forming diblock copolymer melts using the self-consistent-field theory. The micelles are shown to correspond to strong, activated, localized composition fluctuations in the disordered state due to finite molecular weights. By taking into account the translational entropy of the micelles, we obtain the concentration and the free energy of the disordered micelles. The critical micelle temperature (in terms of the familiar combination χN), operationally defined to correspond to the onset of sufficient number of micelles in the system, is identified by invoking a criterion involving the concentration of micelles. The disordered micelles are part of the disordered phase, and the only phase transition between the disordered state and the ordered phase is the order−disorder transition (ODT). However, there exists a sharply defined temperature (higher than the critical micelle temperature), which we term the micelle dissociation temperature, beyond which micelles with finite lifetimes become impossible. The range of χN for the disordered micelles to be observable shrinks as N-1/2 with increasing degrees of polymerization N of the copolymers. In the infinite molecular weight limit, the window vanishes and the mean-field phase diagram calculated by Matsen and Bates is recovered. The disordered micelles, as a part of the disordered phase, contribute to the increased scattering intensity and the low-q shift of the structure factor in diblock copolymer melts near the ODT.

45 citations

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

  • ...In a self-consistent-field calculation, it was shown (Wang et al., 2005) that the micelles are formed via a thermally activated process, with a free energy barrier vanishing at the mean-field spinodal....

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  • ...More recently, Wang et al. (2005) examined the nature of the disordered spherical micelles and their connection to concentration fluctuations using the self-consistent-field theory....

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  • ...It is shown (Wang et al., 2005) that disordered micelles can appear in large numbers before the ordering transition only for not-too-long chains; for very long chains, the ODT will set in before the disordered micelles reach a considerable concentration, essentially precluding the disordered micelles from being a distinct intervening phase between the featureless disordered state and the ordered (fcc or bcc) phases....

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Journal Article•DOI•
Phase transition from disordered sphere to hex-cylinder via transient ordering into bcc-sphere in SIS triblock copolymer

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Norihiro Sota1, Naoki Sakamoto1, Kenji Saijo1, Takeji Hashimoto1•
Kyoto University1
23 May 2003-Macromolecules
TL;DR: In this paper, the ordering processes induced by temperature drop were investigated in situ and at real time by using time-resolved small-angle X-ray scattering, and the transient microdomain structures developed during the ordering proces.
Abstract: We have investigated the ordering processes from the disordered-sphere phase (designated hereafter disordered sphere), where spherical microdomains exist but they have only a short-range liquidlike order, to the phase of hexagonally packed cylindrical microdomains (designated hereafter hex-cylinder), induced by the temperature drop (T-drop). The block copolymer studied is a compositionally asymmetric polystyrene-block-polyisoprene-block-polystyrene triblock copolymer and forms disordered sphere above the order−disorder transition temperature involving the lattice disordering−ordering transition temperature, TODT or TLDOT, spheres in a body-centered-cubic lattice (designated hereafter bcc-sphere) below TLDOT but above the order−order transition (OOT) temperature, TOOT, and hex-cylinder below TOOT. The ordering processes induced by T-drop were explored in situ and at a real time by using time-resolved small-angle X-ray scattering, and the transient microdomain structures developed during the ordering proces...

43 citations

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

  • ...The most dramatic manifestation of the first step is the existence of disordered-spherical-micelle state in highly asymmetric copolymer melts, which almost has the appearance of a distinct phase between the featureless disordered phase and the bcc-ordered phase (Adams et al., 1994, 1996; Schwab and Stühn, 1996; Kim et al., 1999; Han et al., 2000; Sota et al., 2003; Choi et al., 2003; Wang et al., 2002)....

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  • ...…highly asymmetric copolymer melts, which almost has the appearance of a distinct phase between the featureless disordered phase and the bcc-ordered phase (Adams et al., 1994, 1996; Schwab and Stühn, 1996; Kim et al., 1999; Han et al., 2000; Sota et al., 2003; Choi et al., 2003; Wang et al., 2002)....

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  • ...However, experiments show that between the featureless disordered phase and the ordered bcc phase, there exists an intervening disordered-micelle state (Adams et al., 1994, 1996; Schwab and Stühn, 1996; Kim et al., 1999; Han et al., 2000; Sota et al., 2003; Choi et al., 2003; Wang et al., 2002; Semenov, 1989; Dormidontova and Lodge, 2001)....

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Journal Article•DOI•
Thermodynamics of cell adhesion. II. Freely mobile repellers.

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D.C. Torney, Micah Dembo, G.I. Bell
01 Feb 1986-Biophysical Journal
TL;DR: The equilibrium adhesion of a cell or vesicle to a substrate is analyzed in a theoretical model in which two types of mobile molecules in the cell membrane are of interest: receptors that can form bonds with fixed ligands in the substrate and repellers that repel the substrate.

41 citations

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

  • ...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)....

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  • ...In the classical model of cell adhesion proposed by Bell, Dembo, and Bongrand (Bell, 1978; Bell et al., 1984; Torney et al., 1986; Dembo and Bell, 1987) (illustrated in Fig....

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  • ...1 Cell adhesion revisited Bell and co-workers (Bell, 1978; Bell et al., 1984; Torney et al., 1986) first proposed that cell adhesion is a net result of specific ligand-receptor binding and non-specific steric repulsion due to repelling molecules on the cell surface....

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  • ...The average tether length (contour length) of integrins and selectins on lymphocyte cells is of order 10nm (Springer, 1990), which is comparable to the estimation in the Bell papers (Bell, 1978; Bell et al., 1984; Torney et al., 1986)....

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  • ...Bell and co-workers (Bell, 1978; Bell et al., 1984; Torney et al., 1986) suggested that the 2D binding constant should be related to the 3D binding constant as...

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Journal Article•DOI•
Adhesion-induced lateral phase separation in membranes

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Shigeyuki Komura1, David Andelman2•
Weizmann Institute of Science1, Tel Aviv University2
01 Nov 2000-European Physical Journal E
TL;DR: Adhesion between membranes is studied using a phenomenological model, where the inter-membrane distance is coupled to the concentration of sticker molecules on the membranes, which mainly considers the case where the sticker molecules form bridges and adhere directly to both membranes.
Abstract: Adhesion between membranes is studied using a phenomenological model, where the inter-membrane distance is coupled to the concentration of sticker molecules on the membranes. The model applies to both adhesion of two flexible membranes and to adhesion of one flexible membrane onto a second membrane supported on a solid substrate. We mainly consider the case where the sticker molecules form bridges and adhere directly to both membranes. The calculated mean-field phase diagrams show an upward shift of the transition temperature indicating that the lateral phase separation in the membrane is enhanced due to the coupling effect. Hence the possibility of adhesion-induced lateral phase separation is predicted. For a particular choice of the parameters, the model exhibits a tricritical behavior. We also discuss the non-monotonous shape of the inter-membrane distance occurring when the lateral phase separation takes place. The inter-membrane distance relaxes to the bulk values with two symmetric overshoots. Adhesion mediated by other types of stickers is also considered.

39 citations

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01 Jan 2011-Advances on Planar Lipid Bilayers and Liposomes
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Adhesion-induced phase behavior of multicomponent membranes.

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Differences between non-specific and bio-specific, and between equilibrium and non-equilibrium, interactions in biological systems.

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01 Nov 2005-Quarterly Reviews of Biophysics
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Mauro Manno, Mauro Manno, A. Emanuele, A. Emanuele, Vincenzo Martorana, Donatella Bulone, P.L. San Biagio, P.L. San Biagio, M. B. Palma-Vittorelli, M. B. Palma-Vittorelli, M. U. Palma, M. U. Palma 
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