Entropic forces stabilize diverse emergent structures in colloidal membranes

Kang, Louis; Gibaud, Thomas; Dogic, Zvonimir; Lubensky, T. C.

doi:10.1039/c5sm02038g

Cited by 38 publications

(72 citation statements)

References 58 publications

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“…The viruses self-assemble into monolayers that exhibit fluid-like dynamics internally (10) and sediment to the bottom of glass containers, which are coated with a polyacrylamide brush to suppress depletion-induced virus-wall attractions (22). The rich physics and phenomenology of membranes formed from singlevirus species have been thoroughly studied (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)19). However, two-species membranes demonstrate a novel set of behaviors that are not adequately understood (18).…”

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confidence: 99%

Chiral twist drives raft formation and organization in membranes composed of rod-like particles

Kang

Lubensky

2016

Proc. Natl. Acad. Sci. U.S.A.

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Lipid rafts are hypothesized to facilitate protein interaction, tension regulation, and trafficking in biological membranes, but the mechanisms responsible for their formation and maintenance are not clear. Insights into many other condensed matter phenomena have come from colloidal systems, whose micron-scale particles mimic basic properties of atoms and molecules but permit dynamic visualization with single-particle resolution. Recently, experiments showed that bidisperse mixtures of filamentous viruses can self-assemble into colloidal monolayers with thermodynamically stable rafts exhibiting chiral structure and repulsive interactions. We quantitatively explain these observations by modeling the membrane particles as chiral liquid crystals. Chiral twist promotes the formation of finite-sized rafts and mediates a repulsion that distributes them evenly throughout the membrane. Although this system is composed of filamentous viruses whose aggregation is entropically driven by dextran depletants instead of phospholipids and cholesterol with prominent electrostatic interactions, colloidal and biological membranes share many of the same physical symmetries. Chiral twist can contribute to the behavior of both systems and may account for certain stereospecific effects observed in molecular membranes. membrane rafts | liquid crystals | chirality | self-assembly | colloids F ilamentous viruses have proved to be a fruitful colloidal system (1-19). They serve as monodisperse, rigid, and chiral rods that are ∼1 µm in length and interact effectively through hard-core repulsion (2, 7). When suspended in an aqueous solution at increasing concentrations, they transition from a disordered isotropic phase to a cholesteric (chiral nematic) phase characterized by alignment along a director field that twists with a preferred handedness and wavelength (1, 6). The addition of a nonadsorbing polymer such as dextran induces lateral virusvirus attraction via the depletion interaction (10,12,20,21). The viruses self-assemble into monolayers that exhibit fluid-like dynamics internally (10) and sediment to the bottom of glass containers, which are coated with a polyacrylamide brush to suppress depletion-induced virus-wall attractions (22). The rich physics and phenomenology of membranes formed from singlevirus species have been thoroughly studied (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)19). However, two-species membranes demonstrate a novel set of behaviors that are not adequately understood (18). We review these behaviors now before describing a theory that can explain them.fd-Y21M and M13KO7, which we shorten to fd and M13 for convenience, are two species of filamentous virus that have slightly different lengths and form cholesteric phases of opposite handednesses (Table 1 and Fig. 1A). Membranes composed of both fd and M13 viruses are circular with interior particles aligned largely perpendicularly to the membrane plane and edge particles tilted azimuthally, as in single-species membranes (13). At low dextran concentrations, the two spec...

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confidence: 99%

Chiral twist drives raft formation and organization in membranes composed of rod-like particles

Kang

Lubensky

2016

Proc. Natl. Acad. Sci. U.S.A.

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“…References [5] and [6] present a coherent theory based on entropy of the depletants, and to a lesser extent than of viruses within the membranes, and a Frank description of twisting of the viruses relative to membrane normals. The predictions of this theory are in quantitative agreement with essentially all of the measurements of from the Dogic lab.…”

Section: Membranes Of Filamentous Virusesmentioning

confidence: 99%

“…This article, based on my plenary lecture at ILCC 2016 will review recent work done at the University of Pennsylvania on two separate topics: chromonic liquid crystals in confined geometries [1][2][3][4], carried out mostly in Arjun Yodh's lab by Joonwoo Park and Zoey Davidson with some theoretical assistance from me and my student Louis Kang, and a theory, which is mostly the work of Louis Kang [5,6], for multi-micron-sized two-dimensional membranes composed of filamentous viruses stabilized by depletants studied in exquisite detail by Zvonimir Dogic and collaborators [7,8].…”

Section: Introductionmentioning

confidence: 99%

Confined chromonics and viral membranes

Lubensky

2017

Molecular Crystals and Liquid Crystals

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“…[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]), colloidal membranes and smectic stacks have been the subject of more recent modeling (e.g. [4,5,7,[9][10][11][40][41][42][43][44][45][46][47]). Most relevant to the current study, Yang et al [4] carried out numerical simulations of the fd -depletant system, modeling the viruses as hard spherocylinders of diameter σ and length L. The depletant was represented by the Asakura-Osawa (AO) model [16,48], where the polymers are modeled as ghost spheres which freely interpenetrate each other but interact with the rods via an excluded volume interaction.…”

Section: Introductionmentioning

confidence: 99%

“…Of particular interest in recent years [1][2][3][4][5][6][7][8][9][10][11] are assemblies of fd viruses in the presence of a polymer depletant which generates an attractive force between the viruses. Each virus is a rod of roughly one micron in length; the flexibility of the rods can be controlled by molecular engineering and highly monodisperse systems can be fabricated.…”

Section: Introductionmentioning

confidence: 99%

Probing a self-assembledfdvirus membrane with a microtubule

2016

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The self-assembly of highly anisotropic colloidal particles leads to a rich variety of morphologies, whose properties are just beginning to be understood. This article uses computer simulations to probe a particle-scale perturbation of a commonly studied colloidal assembly, a monolayer membrane composed of rodlike fd viruses in the presence of a polymer depletant. Motivated by experiments currently in progress, we simulate the interaction between a microtubule and a monolayer membrane as the microtubule "pokes" and penetrates the membrane face-on. Both the viruses and the microtubule are modeled as hard spherocylinders of the same diameter, while the depletant is modeled using ghost spheres. We find that the force exerted on the microtubule by the membrane is zero either when the microtubule is completely outside the membrane or when it has fully penetrated the membrane. The microtubule is initially repelled by the membrane as it begins to penetrate but experiences an attractive force as it penetrates further. We assess the roles played by translational and rotational fluctuations of the viruses and the osmotic pressure of the polymer depletant. We find that rotational fluctuations play a more important role than the translational ones. The dependence on the osmotic pressure of the depletant of the width and height of the repulsive barrier and the depth of the attractive potential well is consistent with the assumed depletion-induced attractive interaction between the microtubule and viruses. We discuss the relevance of these studies to the experimental investigations.

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Entropic forces stabilize diverse emergent structures in colloidal membranes

Cited by 38 publications

References 58 publications

Chiral twist drives raft formation and organization in membranes composed of rod-like particles

Chiral twist drives raft formation and organization in membranes composed of rod-like particles

Confined chromonics and viral membranes

Probing a self-assembledfdvirus membrane with a microtubule

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