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
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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: In this article, it was shown that the competition between interactions on different length scales can cause a glass transition in a system with no explicitly quenched disorder, and a universal criterion for the emergence of an exponentially large number of metastable configurations that leads to a finite configurational entropy and a landscape dominated viscous flow.
Abstract: We show that the competition between interactions on different length scales, as relevant for the formation of stripes in doped Mott insulators, can cause a glass transition in a system with no explicitly quenched disorder. We analytically determine a universal criterion for the emergence of an exponentially large number of metastable configurations that leads to a finite configurational entropy and a landscape dominated viscous flow. We demonstrate that glassines is unambiguously tied to a new length scale which characterizes the typical length over which defects and imperfections in the stripe pattern are allowed to wander over long times.
54 citations
"Interplay Between Long-Range And Sh..." refers background or methods or result in this paper
...It has been shown that F(q) is equivalent to the long-time correlation function in the conventional mode-coupling approach (Monasson, 1995; Westfahl et al., 2001; Kirkpatrick and Thirumalai, 1989)....
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...TA defined in this way coincides with the dynamic-transition temperature in mean-field— spin-glass models characterized by the appearance of drastically slow dynamic relaxation (Monasson, 1995; Westfahl et al., 2001)....
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...In Chapter 3 we adapt the replica approach by Schmalian, Wolynes, and co-workers (Westfahl et al., 2001; Schmalian and Wolynes, 2000) and study the phase diagram in the system of diblock copolymer melts....
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...Our work follows a similar approach to that employed by Schmalian and co-workers (Schmalian and Wolynes, 2000; Westfahl et al., 2001)....
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...This approach was first proposed by Monasson (1995) and subsequently employed by a number of authors in studying structural glass transitions (Mézard and Parisi, 2000; Coluzzi et al., 2000; Schmalian and Wolynes, 2000; Westfahl et al., 2001; Wu et al., 2004)....
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TL;DR: This chapter discusses the thermodynamics of cellAdhesion and illustrates the principles involved in taking a thermodynamic approach in modeling cell adhesion, and demonstrates the power of thermodynamics in its being able to integrate a large number of complicated variables into an effective computational and predictive tool.
Abstract: Publisher Summary This chapter discusses the thermodynamics of cell adhesion and illustrates the principles involved in taking a thermodynamic approach in modeling cell adhesion. The detailed formulation and analysis of an elementary example––adhesion of a cell to a large flat surface, herein called the “substrate” is presented. The simple model of cell–substrate adhesion is presented and analyzed. This model demonstrates the power of thermodynamics in its being able to integrate a large number of complicated variables into an effective computational and predictive tool. It views cell adhesion as resulting from the formation of specific receptor-site bonds; the net effect of all other forces between cell and substrate is taken to be repulsive. The chemical potentials of the free receptors and free sites are also discussed. The repulsive potential, Γ(S), is defined as the mechanical work that is done against nonspecific forces to bring a unit area of membrane from an infinite separation to a separation of S. The forces resisting adhesion arise mainly from a combination of two effects: (1) electrostatic repulsion among negative changes associated with the surfaces and (2) the so-called “steric stabilization effect.” List of the various physical parameters that characterize cell–substrate adhesion according to model is tabulated.
54 citations
"Interplay Between Long-Range And Sh..." refers background in this paper
...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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TL;DR: It is shown that the interplay of specific attractive and generic repulsive interactions can lead to the formation of a potential barrier which induces a line tension between bound and unbound membrane segments which results in lateral phase separation during adhesion.
Abstract: Biomimetic membranes in contact with a planar substrate or a second membrane are studied theoretically. The membranes contain specific adhesion molecules (stickers) which are attracted by the second surface. In the absence of stickers, the trans-interaction between the membrane and the second surface is assumed to be repulsive at short separations. It is shown that the interplay of specific attractive and generic repulsive interactions can lead to the formation of a potential barrier. This barrier induces a line tension between bound and unbound membrane segments which results in lateral phase separation during adhesion. The mechanism for adhesion-induced phase separation is rather general, as is demonstrated by considering two distinct cases involving: i) stickers with a linear attractive potential, and ii) stickers with a short-ranged square-well potential. In both cases, membrane fluctuations reduce the potential barrier and, therefore, decrease the tendency of phase separation.
53 citations
"Interplay Between Long-Range And Sh..." refers background 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)....
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TL;DR: In this article, phase diagrams of thermoreversible gels are derived by the use of two different conventional postgel treatments, i.e., Flory's treatment and Stockmayer's treatment.
Abstract: Phase diagrams of thermoreversible gels are derived by the use of two different conventional postgel treatments, ie, Flory's treatment and Stockmayer's treatment Phase diagrams by Flory's treatment, which allows cycle formation in the gel network, often show two critical points for intermediate association constants, one in the sol region and the other in the gel region In such a case three-phase equilibrium temperature appears Existence of a critical solution point in the gel region suggests the possibility of phase separation into a dilute gel and a concentrated gel One of these two critical points is a conventional type that lies on the stable coexistence curve (binodal), but the other one may lie on the metastable binodal In contrast, phase diagrams by Stockmayer's treatment, which strictly excludes cycle formation in the gel network, often lead to the appearance of a tricritical point (TCP) where sol/gel transition curve intersects with the binodal line This treatment gives no critical soluti
50 citations
"Interplay Between Long-Range And Sh..." refers background in this paper
...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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TL;DR: A minimalist model is obtained that captures experimentally observed phenomenology of the immunological synapse, which is implicated in information transfer between cells, and is characterized by different spatial patterns of receptors at different stages in the life cycle of T cells.
Abstract: The immunological synapse is a patterned collection of different types of receptors and ligands that forms in the intercellular junction between T cells and antigen presenting cells during recognition. The synapse is implicated in information transfer between cells, and is characterized by different spatial patterns of receptors at different stages in the life cycle of T cells. We obtain a minimalist model that captures this experimentally observed phenomenology. A functional renormalization group analysis provides further insights.
50 citations
"Interplay Between Long-Range And Sh..." refers background in this paper
...The fact that the synapses between premature T-cells (thymocytes) and the APC do not show a well-developed contact with TCR-MHC bonds could be due to either insufficient TCR bonds (Lee et al., 2003; Raychaudhuri et al., 2003), or the absence of active mechanisms to overcome the high energy barrier....
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...Due to their different spatial extensions (the natural size of the integrin-ligand bond is ∼40nm, and is about 15nm for the TCR-MHC complex), the binary system consisting of TCR and integrin binding should exhibit a double-well interaction potential (Raychaudhuri et al., 2003)....
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