51
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Pinson MB, Witten TA. Signal transmissibility in marginal granular materials. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:495102. [PMID: 27731309 DOI: 10.1088/0953-8984/28/49/495102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We examine the 'transmissibility' of a simulated two-dimensional pack of frictionless disks formed by confining dilute disks in a shrinking, periodic box to the point of mechanical stability. Two opposite boundaries are then removed, thus allowing a set of free motions. Small free displacements on one boundary then induce proportional displacements on the opposite boundary. Transmissibility is the ability to distinguish different perturbations by their distant responses. We assess transmissibility by successively identifying free orthonormal modes of motion that have the smallest distant responses. The last modes to be identified in this 'pessimistic' basis are the most transmissive. The transmitted amplitudes of these most transmissive modes fall off exponentially with mode number. Similar exponential falloff is seen in a simple elastic medium, though the responsible modes differ greatly in structure in the two systems. Thus the marginal pack's transmissibility is qualitatively similar to that of a simple elastic medium. We compare our results with recent findings based on the projection of the space of free motion onto interior sites.
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Affiliation(s)
- Matthew B Pinson
- James Franck Institute, University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA
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52
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Philippova OE, Shibaev AV, Muravlev DA, Mityuk DY. Structure and Rheology of Solutions and Gels of Stiff Polyelectrolyte at High Salt Concentration. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01392] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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53
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Rizzi LG, Auer S, Head DA. Importance of non-affine viscoelastic response in disordered fibre networks. SOFT MATTER 2016; 12:4332-4338. [PMID: 27079274 DOI: 10.1039/c6sm00139d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Disordered fibre networks are ubiquitous in nature and have a wide range of industrial applications as novel biomaterials. Predicting their viscoelastic response is straightforward for affine deformations that are uniform over all length scales, but when affinity fails, as has been observed experimentally, modelling becomes challenging. Here we present a numerical methodology, related to an existing framework for amorphous packings, to predict the steady-state viscoelastic spectra and degree of affinity for disordered fibre networks driven at arbitrary frequencies. Applying this method to a peptide gel model reveals a monotonic increase of the shear modulus as the soft, non-affine normal modes are successively suppressed as the driving frequency increases. In addition to being dominated by fibril bending, these low frequency network modes are also shown to be delocalised. The presented methodology provides insights into the importance of non-affinity in the viscoelastic response of peptide gels, and is easily extendible to all types of fibre networks.
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Affiliation(s)
- L G Rizzi
- Departamento de Física, Universidade Federal de Viçosa, 36570-900, Viçosa, Brazil and School of Chemistry, University of Leeds, LS2 9JT, Leeds, UK
| | - S Auer
- School of Chemistry, University of Leeds, LS2 9JT, Leeds, UK
| | - D A Head
- School of Computing, University of Leeds, LS2 9JT, Leeds, UK.
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54
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Ballesta P, Petekidis G. Creep and aging of hard-sphere glasses under constant stress. Phys Rev E 2016; 93:042613. [PMID: 27176358 DOI: 10.1103/physreve.93.042613] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Indexed: 06/05/2023]
Abstract
We investigate the aging behavior of glassy suspensions of nearly hard-sphere colloids submitted to a constant shear stress. For low stresses, below the yield stress, the system is subject to creep motion. As the sample ages, the shear rate exhibits a power-law decrease with time with exponents that depend on the sample age. We use a combination of rheological experiments with time-resolved photon correlation spectroscopy to investigate the time evolution of the sample dynamics under shear on various time and length scales. Long-time light-scattering experiments reveal the occurrence of microscopic rearrangement events that are linked with the macroscopic strain deformation of the sample. Dynamic time sweep experiments indicate that while the internal microscopic dynamics slow down continuously with waiting time, the storage and loss moduli are almost constant after a fast, weak decrease, resembling the behavior of quenched systems with partially frozen-in stresses.
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Affiliation(s)
- P Ballesta
- Faculdade de Engenharia da Universidade do Porto - CEFT - Dep. Engenharia Química, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
- IESL-FORTH, PO Box 1527, Heraklion 71110, Crete, Greece
| | - G Petekidis
- IESL-FORTH, PO Box 1527, Heraklion 71110, Crete, Greece
- Department of Materials Science & Technology, University of Crete, Greece
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55
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Nabavi SS, Hartmann MA. Weak reversible cross links may decrease the strength of aligned fiber bundles. SOFT MATTER 2016; 12:2047-2055. [PMID: 26750612 DOI: 10.1039/c5sm02614h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Reversible cross-linking is an effective strategy to specifically tailor the mechanical properties of polymeric materials that can be found in a variety of biological as well as man-made materials. Using a simple model in this paper the influence of weak, reversible cross-links on the mechanical properties of aligned fiber bundles is investigated. Special emphasis in this analysis is put on the strength of the investigated structures. Using Monte Carlo methods two topologies of cross-links exceeding the strength of the covalent backbone are studied. Most surprisingly only two cross-links are sufficient to break the backbone of a multi chain system, resulting in a reduced strength of the material. The found effect crucially depends on the ratio of inter- to intra-chain cross-links and, thus, on the grafting density that determines this ratio.
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Affiliation(s)
- S Soran Nabavi
- Institute of Physics, Montanuniversitaet Leoben, Franz-Josef Strasse 18, 8700 Leoben, Austria.
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56
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Wu JH, Jia Q. The heterogeneous energy landscape expression of KWW relaxation. Sci Rep 2016; 6:20506. [PMID: 26879824 PMCID: PMC4754662 DOI: 10.1038/srep20506] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 01/05/2016] [Indexed: 11/09/2022] Open
Abstract
Here we show a heterogeneous energy landscape approach to describing the Kohlrausch-Williams-Watts (KWW) relaxation function. For a homogeneous dynamic process, the distribution of free energy landscape is first proposed, revealing the significance of rugged fluctuations. In view of the heterogeneous relaxation given in two dynamic phases and the transmission coefficient in a rate process, we obtain a general characteristic relaxation time distribution equation for the KWW function in a closed, analytic form. Analyses of numerical computation show excellent accuracy, both in time and frequency domains, in the convergent performance of the heterogeneous energy landscape expression and shunning the catastrophic truncations reported in the previous work. The stretched exponential β, closely associated to temperature and apparent correlation with one dynamic phase, reveals a threshold value of 1/2 defining different behavior of the probability density functions. Our work may contribute, for example, to in-depth comprehension of the dynamic mechanism of glass transition, which cannot be provided by existing approaches.
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Affiliation(s)
- J H Wu
- Peter Grünberg Research Center, Nanjing University of Posts and Telecommunications, Nanjing 210003, China.,Research Institute of Engineering and Technology, Korea University, Seoul 136-713, South Korea.,School of Life Sciences, Shandong University, Jinan 250100, China
| | - Q Jia
- Department of Management, Hohai University, Nanjing 211100, China
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57
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Metzler R, Jeon JH, Cherstvy AG. Non-Brownian diffusion in lipid membranes: Experiments and simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2451-2467. [PMID: 26826272 DOI: 10.1016/j.bbamem.2016.01.022] [Citation(s) in RCA: 126] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 01/21/2016] [Accepted: 01/23/2016] [Indexed: 12/14/2022]
Abstract
The dynamics of constituents and the surface response of cellular membranes-also in connection to the binding of various particles and macromolecules to the membrane-are still a matter of controversy in the membrane biophysics community, particularly with respect to crowded membranes of living biological cells. We here put into perspective recent single particle tracking experiments in the plasma membranes of living cells and supercomputing studies of lipid bilayer model membranes with and without protein crowding. Special emphasis is put on the observation of anomalous, non-Brownian diffusion of both lipid molecules and proteins embedded in the lipid bilayer. While single component, pure lipid bilayers in simulations exhibit only transient anomalous diffusion of lipid molecules on nanosecond time scales, the persistence of anomalous diffusion becomes significantly longer ranged on the addition of disorder-through the addition of cholesterol or proteins-and on passing of the membrane lipids to the gel phase. Concurrently, experiments demonstrate the anomalous diffusion of membrane embedded proteins up to macroscopic time scales in the minute time range. Particular emphasis will be put on the physical character of the anomalous diffusion, in particular, the occurrence of ageing observed in the experiments-the effective diffusivity of the measured particles is a decreasing function of time. Moreover, we present results for the time dependent local scaling exponent of the mean squared displacement of the monitored particles. Recent results finding deviations from the commonly assumed Gaussian diffusion patterns in protein crowded membranes are reported. The properties of the displacement autocorrelation function of the lipid molecules are discussed in the light of their appropriate physical anomalous diffusion models, both for non-crowded and crowded membranes. In the last part of this review we address the upcoming field of membrane distortion by elongated membrane-binding particles. We discuss how membrane compartmentalisation and the particle-membrane binding energy may impact the dynamics and response of lipid membranes. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- R Metzler
- Institute for Physics & Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany; Department of Physics, Tampere University of Technology, 33101 Tampere, Finland.
| | - J-H Jeon
- Korea Institute for Advanced Study (KIAS), Seoul, Republic of Korea
| | - A G Cherstvy
- Institute for Physics & Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany
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58
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Myung JS, Winkler RG, Gompper G. Self-organization in suspensions of end-functionalized semiflexible polymers under shear flow. J Chem Phys 2015; 143:243117. [PMID: 26723602 DOI: 10.1063/1.4933368] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The nonequilibrium dynamical behavior and structure formation of end-functionalized semiflexible polymer suspensions under flow are investigated by mesoscale hydrodynamic simulations. The hybrid simulation approach combines the multiparticle collision dynamics method for the fluid, which accounts for hydrodynamic interactions, with molecular dynamics simulations for the semiflexible polymers. In equilibrium, various kinds of scaffold-like network structures are observed, depending on polymer flexibility and end-attraction strength. We investigate the flow behavior of the polymer networks under shear and analyze their nonequilibrium structural and rheological properties. The scaffold structure breaks up and densified aggregates are formed at low shear rates, while the structural integrity is completely lost at high shear rates. We provide a detailed analysis of the shear- rate-dependent flow-induced structures. The studies provide a deeper understanding of the formation and deformation of network structures in complex materials.
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Affiliation(s)
- Jin Suk Myung
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Roland G Winkler
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Gerhard Gompper
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
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59
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Orsi D, Guzmán E, Liggieri L, Ravera F, Ruta B, Chushkin Y, Rimoldi T, Cristofolini L. 2D dynamical arrest transition in a mixed nanoparticle-phospholipid layer studied in real and momentum spaces. Sci Rep 2015; 5:17930. [PMID: 26658474 PMCID: PMC4674700 DOI: 10.1038/srep17930] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 11/06/2015] [Indexed: 12/26/2022] Open
Abstract
We investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For this, we combine micro-tracking in real-space with measurement in momentum-space via x-ray photon-correlation spectroscopy and Digital Fourier Microscopy. Using these complementary techniques, we extend the spatial range of investigation beyond the limits of each one. We find a dynamical transition from Brownian diffusion to an arrested state driven by compression, characterized by intermittent rearrangements, compatible with a repulsive glass phase. The rearrangement and relaxation of the monolayer structure results dramatically hindered by the presence of NPs, which is relevant to explain some the mechanical features observed for the dynamic surface pressure response of these systems and which can be relevant for the respiratory physiology and for future drug-delivery composite systems.
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Affiliation(s)
- Davide Orsi
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, Parma, Italy
| | - Eduardo Guzmán
- Consiglio Nazionale delle Ricerche - Istituto per l’Energetica e le Interfasi, U.O.S. Genova (CNR IENI), Genova (Italy)
| | - Libero Liggieri
- Consiglio Nazionale delle Ricerche - Istituto per l’Energetica e le Interfasi, U.O.S. Genova (CNR IENI), Genova (Italy)
| | - Francesca Ravera
- Consiglio Nazionale delle Ricerche - Istituto per l’Energetica e le Interfasi, U.O.S. Genova (CNR IENI), Genova (Italy)
| | - Beatrice Ruta
- ESRF- The European Synchrotron, CS 40220, 38043 Grenoble Cedex 9, France
| | - Yuriy Chushkin
- ESRF- The European Synchrotron, CS 40220, 38043 Grenoble Cedex 9, France
| | - Tiziano Rimoldi
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, Parma, Italy
| | - Luigi Cristofolini
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, Parma, Italy
- Consiglio Nazionale delle Ricerche - Istituto per l’Energetica e le Interfasi, U.O.S. Genova (CNR IENI), Genova (Italy)
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60
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Premchandar A, Kupniewska A, Tarnowski K, Mücke N, Mauermann M, Kaus-Drobek M, Edelman A, Herrmann H, Dadlez M. Analysis of distinct molecular assembly complexes of keratin K8 and K18 by hydrogen–deuterium exchange. J Struct Biol 2015; 192:426-440. [DOI: 10.1016/j.jsb.2015.10.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 09/24/2015] [Accepted: 10/01/2015] [Indexed: 02/06/2023]
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61
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Srivastava S, Agarwal P, Mangal R, Koch DL, Narayanan S, Archer LA. Hyperdiffusive Dynamics in Newtonian Nanoparticle Fluids. ACS Macro Lett 2015; 4:1149-1153. [PMID: 35614796 DOI: 10.1021/acsmacrolett.5b00319] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hyperdiffusive relaxations in soft glassy materials are typically associated with out-of-equilibrium states, and nonequilibrium physics and aging are often invoked in explaining their origins. Here, we report on hyperdiffusive motion in model soft materials comprised of single-component polymer-tethered nanoparticles, which exhibit a readily accessible Newtonian flow regime. In these materials, polymer-mediated interactions lead to strong nanoparticle correlations, hyperdiffusive relaxations, and unusual variations of properties with temperature. We propose that hyperdiffusive relaxations in such materials can arise naturally from nonequilibrium or non-Brownian volume fluctuations forced by equilibrium thermal rearrangements of the particle pair orientations corresponding to equilibrated shear modes.
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Affiliation(s)
- Samanvaya Srivastava
- School
of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
| | - Praveen Agarwal
- School
of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
| | - Rahul Mangal
- School
of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
| | - Donald L. Koch
- School
of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
| | - Suresh Narayanan
- Advanced
Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Lynden A. Archer
- School
of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
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62
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Du ZP, Wu BL, Xie JJ, Lin XH, Qiu XY, Zhan XF, Wang SH, Shen JH, Li EM, Xu LY. Network Analyses of Gene Expression following Fascin Knockdown in Esophageal Squamous Cell Carcinoma Cells. Asian Pac J Cancer Prev 2015. [DOI: 10.7314/apjcp.2015.16.13.5445] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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63
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Mechanics and dynamics of reconstituted cytoskeletal systems. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1853:3038-42. [PMID: 26130089 DOI: 10.1016/j.bbamcr.2015.06.013] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 06/22/2015] [Accepted: 06/23/2015] [Indexed: 01/21/2023]
Abstract
The intracellular cytoskeleton is an active dynamic network of filaments and associated binding proteins that control key cellular properties, such as cell shape and mechanics. Due to the inherent complexity of the cell, reconstituted model systems have been successfully employed to gain an understanding of the fundamental physics governing cytoskeletal processes. Here, we review recent advances and key aspects of these reconstituted systems. We focus on the importance of assembly kinetics and dynamic arrest in determining network mechanics, and highlight novel emergent behavior occurring through interactions between cytoskeletal components in more complex networks incorporating multiple biopolymers and molecular motors.
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64
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Buzzaccaro S, Alaimo MD, Secchi E, Piazza R. Spatially-resolved heterogeneous dynamics in a strong colloidal gel [corrected]. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:194120. [PMID: 25924184 DOI: 10.1088/0953-8984/27/19/194120] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We re-examine the classical problem of irreversible colloid aggregation, showing that the application of Digital Fourier Imaging (DFI), a class of optical correlation methods that combine the power of light scattering and imaging, allows one to pick out novel useful evidence concerning the restructuring processes taking place in a strong colloidal gel. In particular, the spatially-resolved displacement fields provided by DFI strongly suggest that the temporally-intermittent local rearrangements taking place in the course of gel ageing are characterized by very long-ranged spatial correlations.
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Affiliation(s)
- Stefano Buzzaccaro
- Department of Chemistry, Chemical Engineering and Material Science (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy
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65
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Abstract
Cell physiological processes require the regulation and coordination of both mechanical and dynamical properties of the actin cytoskeleton. Here we review recent advances in understanding the mechanical properties and stability of actin filaments and how these properties are manifested at larger (network) length scales. We discuss how forces can influence local biochemical interactions, resulting in the formation of mechanically sensitive dynamic steady states. Understanding the regulation of such force-activated chemistries and dynamic steady states reflects an important challenge for future work that will provide valuable insights as to how the actin cytoskeleton engenders mechanoresponsiveness of living cells.
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Affiliation(s)
- Enrique M De La Cruz
- From the Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06511 and
| | - Margaret L Gardel
- the Institute for Biophysical Dynamics, James Franck Institute, and Department of Physics, University of Chicago, Chicago, Illinois 60637
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66
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Lewis OL, Guy RD, Allard JF. Actin-myosin spatial patterns from a simplified isotropic viscoelastic model. Biophys J 2015; 107:863-70. [PMID: 25140421 DOI: 10.1016/j.bpj.2014.06.041] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Revised: 05/28/2014] [Accepted: 06/16/2014] [Indexed: 11/30/2022] Open
Abstract
F-actin networks are involved in cell mechanical processes ranging from motility to endocytosis. The mesoscale architecture of assemblies of individual F-actin polymers that gives rise to micrometer-scale rheological properties is poorly understood, despite numerous in vivo and vitro studies. In vitro networks have been shown to organize into spatial patterns when spatially confined, including dense spherical shells inside spherical emulsion droplets. Here we develop a simplified model of an isotropic, compressible, viscoelastic material continually assembling and disassembling. We demonstrate that spherical shells emerge naturally when the strain relaxation rate (corresponding to internal network reorganization) is slower than the disassembly rate (corresponding to F-actin depolymerization). These patterns are consistent with recent experiments, including a collapse of shells to a central high-density focus of F-actin when either assembly or disassembly is reduced with drugs. Our results demonstrate how complex spatio-temporal patterns can emerge without spatially distributed force generation, polar alignment of F-actin polymers, or spatially nonuniform regulation of F-actin by upstream biochemical networks.
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Affiliation(s)
- Owen L Lewis
- Department of Mathematics, University of California at Davis, Davis, California
| | - Robert D Guy
- Department of Mathematics, University of California at Davis, Davis, California
| | - Jun F Allard
- Department of Mathematics, Department of Physics and Astronomy, Center for Complex Biological Systems, University of California at Irvine, Irvine, California.
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67
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Deshpande S, Pfohl T. Real-time dynamics of emerging actin networks in cell-mimicking compartments. PLoS One 2015; 10:e0116521. [PMID: 25785606 PMCID: PMC4364982 DOI: 10.1371/journal.pone.0116521] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Accepted: 12/10/2014] [Indexed: 01/07/2023] Open
Abstract
Understanding the cytoskeletal functionality and its relation to other cellular components and properties is a prominent question in biophysics. The dynamics of actin cytoskeleton and its polymorphic nature are indispensable for the proper functioning of living cells. Actin bundles are involved in cell motility, environmental exploration, intracellular transport and mechanical stability. Though the viscoelastic properties of actin-based structures have been extensively probed, the underlying microstructure dynamics, especially their disassembly, is not fully understood. In this article, we explore the rich dynamics and emergent properties exhibited by actin bundles within flow-free confinements using a microfluidic set-up and epifluorescence microscopy. After forming entangled actin filaments within cell-sized quasi two-dimensional confinements, we induce their bundling using three different fundamental mechanisms: counterion condensation, depletion interactions and specific protein-protein interactions. Intriguingly, long actin filaments form emerging networks of actin bundles via percolation leading to remarkable properties such as stress generation and spindle-like intermediate structures. Simultaneous sharing of filaments in different links of the network is an important parameter, as short filaments do not form networks but segregated clusters of bundles instead. We encounter a hierarchical process of bundling and its subsequent disassembly. Additionally, our study suggests that such percolated networks are likely to exist within living cells in a dynamic fashion. These observations render a perspective about differential cytoskeletal responses towards numerous stimuli.
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Affiliation(s)
- Siddharth Deshpande
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland
| | - Thomas Pfohl
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland
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68
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Li T, Liu L, Hu D, Oloyede A, Xiao Y, Yarlagadda P, Gu Y. Comprehensive Contribution of Filament Thickness and Crosslinker Failure to the Rheological Property of F-actin Cytoskeleton. Cell Mol Bioeng 2015. [DOI: 10.1007/s12195-015-0382-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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69
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Secchi E, Munarin F, Alaimo MD, Bosisio S, Buzzaccaro S, Ciccarella G, Vergaro V, Petrini P, Piazza R. External and internal gelation of pectin solutions: microscopic dynamics versus macroscopic rheology. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:464106. [PMID: 25347466 DOI: 10.1088/0953-8984/26/46/464106] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Pectin is a natural biopolymer that forms, in the presence of divalent cations, ionic-bound gels typifying a large class of biological gels stabilized by non-covalent cross-links. We investigate and compare the kinetics of formation and aging of pectin gels obtained either through external gelation via perfusion of free Ca(2+) ions, or by internal gelation due to the supply of the same ions from the dissolution of CaCO3 nanoparticles. The microscopic dynamics obtained with photon correlation imaging, a novel optical technique that allows obtaining the microscopic dynamics of the sample while retaining the spatial resolution of imaging techniques, is contrasted with macroscopic rheological measurements at constant strain. Pectin gelation is found to display peculiar two-stage kinetics, highlighted by non-monotonic growth in time of both microscopic correlations and gel mechanical strength. These results are compared to those found for alginate, another biopolymer extensively used in food formulation.
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Affiliation(s)
- E Secchi
- Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, 20133 Milano, Italy
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70
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Georgiades P, Pudney PDA, Rogers S, Thornton DJ, Waigh TA. Tea derived galloylated polyphenols cross-link purified gastrointestinal mucins. PLoS One 2014; 9:e105302. [PMID: 25162539 PMCID: PMC4146515 DOI: 10.1371/journal.pone.0105302] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 07/22/2014] [Indexed: 12/24/2022] Open
Abstract
Polyphenols derived from tea are thought to be important for human health. We show using a combination of particle tracking microrheology and small-angle neutron scattering that polyphenols acts as cross-linkers for purified gastrointestinal mucin, derived from the stomach and the duodenum. Both naturally derived purified polyphenols, and green and black tea extracts are shown to act as cross-linkers. The main active cross-linking component is found to be the galloylated forms of catechins. The viscosity, elasticity and relaxation time of the mucin solutions experience an order of magnitude change in value upon addition of the polyphenol cross-linkers. Similarly small-angle neutron scattering experiments demonstrate a sol-gel transition with the addition of polyphenols, with a large increase in the scattering at low angles, which is attributed to the formation of large scale (>10 nm) heterogeneities during gelation. Cross-linking of mucins by polyphenols is thus expected to have an impact on the physicochemical environment of both the stomach and duodenum; polyphenols are expected to modulate the barrier properties of mucus, nutrient absorption through mucus and the viscoelastic microenvironments of intestinal bacteria.
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Affiliation(s)
- Pantelis Georgiades
- Biological Physics, Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
- ISIS Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire, United Kingdom
- * E-mail:
| | - Paul D. A. Pudney
- Strategic Science Group, Unilever Discover, Unilever, Colworth Science Park, Sharnbrook, Bedfordshire, United Kingdom
| | - Sarah Rogers
- ISIS Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire, United Kingdom
| | - David J. Thornton
- Wellcome Trust Centre for Cell Matrix Research, Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Thomas A. Waigh
- Biological Physics, Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
- Photon Science Institute, University of Manchester, Manchester, United Kingdom
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71
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Körnig A, Dong J, Bennet M, Widdrat M, Andert J, Müller F, Schüler D, Klumpp S, Faivre D. Probing the mechanical properties of magnetosome chains in living magnetotactic bacteria. NANO LETTERS 2014; 14:4653-9. [PMID: 25003507 PMCID: PMC4133184 DOI: 10.1021/nl5017267] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The mechanical properties of cytoskeletal networks are intimately involved in determining how forces and cellular processes are generated, directed, and transmitted in living cells. However, determining the mechanical properties of subcellular molecular complexes in vivo has proven to be difficult. Here, we combine in vivo measurements by optical microscopy, X-ray diffraction, and transmission electron microscopy with theoretical modeling to decipher the mechanical properties of the magnetosome chain system encountered in magnetotactic bacteria. We exploit the magnetic properties of the endogenous intracellular nanoparticles to apply a force on the filament-connector pair involved in the backbone formation and stabilization. We show that the magnetosome chain can be broken by the application of external field strength higher than 30 mT and suggest that this originates from the rupture of the magnetosome connector MamJ. In addition, we calculate that the biological determinants can withstand in vivo a force of 25 pN. This quantitative understanding provides insights for the design of functional materials such as actuators and sensors using cellular components.
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Affiliation(s)
- André Körnig
- Department of Biomaterials and Department of
Theory and Bio-Systems, Max Planck Institute
of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
| | - Jiajia Dong
- Department of Biomaterials and Department of
Theory and Bio-Systems, Max Planck Institute
of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
- Department
of Physics and Astronomy, Bucknell University, Lewisburg, Pennsylvania 17837, United States
| | - Mathieu Bennet
- Department of Biomaterials and Department of
Theory and Bio-Systems, Max Planck Institute
of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
| | - Marc Widdrat
- Department of Biomaterials and Department of
Theory and Bio-Systems, Max Planck Institute
of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
| | - Janet Andert
- Department of Biomaterials and Department of
Theory and Bio-Systems, Max Planck Institute
of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
| | - Frank
D. Müller
- Department
1, Microbiology, Ludwig-Maximilians-Universität
München, Großhaderner
Strasse 2-4, 82152 Planegg-Martinsried, Germany
| | - Dirk Schüler
- Department
1, Microbiology, Ludwig-Maximilians-Universität
München, Großhaderner
Strasse 2-4, 82152 Planegg-Martinsried, Germany
| | - Stefan Klumpp
- Department of Biomaterials and Department of
Theory and Bio-Systems, Max Planck Institute
of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
| | - Damien Faivre
- Department of Biomaterials and Department of
Theory and Bio-Systems, Max Planck Institute
of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
- (D.F.)
E-mail:
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72
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Nguyen TD, Gu Y. Determination of Strain-Rate-Dependent Mechanical Behavior of Living and Fixed Osteocytes and Chondrocytes Using Atomic Force Microscopy and Inverse Finite Element Analysis. J Biomech Eng 2014; 136:101004. [DOI: 10.1115/1.4028098] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 07/30/2014] [Indexed: 11/08/2022]
Abstract
The aim of this paper is to determine the strain-rate-dependent mechanical behavior of living and fixed osteocytes and chondrocytes, in vitro. First, atomic force microscopy (AFM) was used to obtain the force–indentation curves of these single cells at four different strain-rates. These results were then employed in inverse finite element analysis (FEA) using modified standard neo-Hookean solid (MSnHS) idealization of these cells to determine their mechanical properties. In addition, a FEA model with a newly developed spring element was employed to accurately simulate AFM evaluation in this study. We report that both cytoskeleton (CSK) and intracellular fluid govern the strain-rate-dependent mechanical property of living cells whereas intracellular fluid plays a predominant role on fixed cells' behavior. In addition, through the comparisons, it can be concluded that osteocytes are stiffer than chondrocytes at all strain-rates tested indicating that the cells could be the biomarker of their tissue origin. Finally, we report that MSnHS is able to capture the strain-rate-dependent mechanical behavior of osteocyte and chondrocyte for both living and fixed cells. Therefore, we concluded that the MSnHS is a good model for exploration of mechanical deformation responses of single osteocytes and chondrocytes. This study could open a new avenue for analysis of mechanical behavior of osteocytes and chondrocytes as well as other similar types of cells.
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Affiliation(s)
- Trung Dung Nguyen
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, Brisbane, Queensland, Australia
| | - YuanTong Gu
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, Brisbane, Queensland, Australia e-mail:
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73
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Müller KW, Bruinsma RF, Lieleg O, Bausch AR, Wall WA, Levine AJ. Rheology of semiflexible bundle networks with transient linkers. PHYSICAL REVIEW LETTERS 2014; 112:238102. [PMID: 24972229 DOI: 10.1103/physrevlett.112.238102] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Indexed: 06/03/2023]
Abstract
We present a theoretical and computational analysis of the rheology of networks made up of bundles of semiflexible filaments bound by transient cross-linkers. Such systems are ubiquitous in the cytoskeleton and can be formed in vitro using filamentous actin and various cross-linkers. We find that their high-frequency rheology is characterized by a scaling behavior that is quite distinct from that of networks of the well-studied single semiflexible filaments. This regime can be understood theoretically in terms of a length-scale-dependent bending modulus for bundles. Next, we observe new dissipative dynamics associated with the shear-induced disruption of the network at intermediate frequencies. Finally, at low frequencies, we encounter a region of non-Newtonian rheology characterized by power-law scaling. This regime is dominated by bundle dissolution and large-scale rearrangements of the network driven by equilibrium thermal fluctuations.
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Affiliation(s)
- Kei W Müller
- Institute for Computational Mechanics, Technische Universität München, 85748 Garching, Germany
| | - Robijn F Bruinsma
- Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095-1596, USA and Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1596, USA
| | - Oliver Lieleg
- Institute for Medical Engineering IMETUM, Technische Universität München, 85748 Garching, Germany
| | - Andreas R Bausch
- Lehrstuhl für Zellbiophysik E27, Physik Department, Technische Universität München, 85748 Garching, Germany
| | - Wolfgang A Wall
- Institute for Computational Mechanics, Technische Universität München, 85748 Garching, Germany
| | - Alex J Levine
- Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095-1596, USA and Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1596, USA and Department of Biomathematics, UCLA, Los Angeles, California 90095-1596, USA
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74
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Myung JS, Taslimi F, Winkler RG, Gompper G. Self-Organized Structures of Attractive End-Functionalized Semiflexible Polymer Suspensions. Macromolecules 2014. [DOI: 10.1021/ma500731d] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jin Suk Myung
- Theoretical Soft Matter and
Biophysics, Institute of Complex Systems, and Institute for Advanced
Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Farzaneh Taslimi
- Theoretical Soft Matter and
Biophysics, Institute of Complex Systems, and Institute for Advanced
Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Roland G. Winkler
- Theoretical Soft Matter and
Biophysics, Institute of Complex Systems, and Institute for Advanced
Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Gerhard Gompper
- Theoretical Soft Matter and
Biophysics, Institute of Complex Systems, and Institute for Advanced
Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
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75
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Persistent super-diffusive motion of Escherichia coli chromosomal loci. Nat Commun 2014; 5:3854. [DOI: 10.1038/ncomms4854] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Accepted: 04/10/2014] [Indexed: 01/15/2023] Open
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76
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Pelc D, Marion S, Požek M, Basletić M. Role of microscopic phase separation in gelation of aqueous gelatin solutions. SOFT MATTER 2014; 10:348-356. [PMID: 24651841 DOI: 10.1039/c3sm52542b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Using a unique home-made cell for four-contact impedance spectroscopy of conductive liquid samples, we establish the existence of two low frequency conductivity relaxations in aqueous solutions of gelatin, in both liquid and gel states. A comparison with diffusion measurements using pulsed field gradient NMR, and circular dichroism spectroscopy, shows that the faster relaxation process is due to gelatin macromolecule self-diffusion. This single molecule diffusion is mostly insensitive to the macroscopic state of the sample, implying that we have a clear separation of gelatin molecules into a free and network-bound phase. Scaling relationships for the self-diffusion indicate that the gelation process is not a percolative phenomenon, but is caused by aggregation of triple helices into a system-spanning fibre network.
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Affiliation(s)
- Damjan Pelc
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, 10000 Zagreb, Croatia.
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77
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Mohan L, Bonnecaze RT, Cloitre M. Microscopic origin of internal stresses in jammed soft particle suspensions. PHYSICAL REVIEW LETTERS 2013; 111:268301. [PMID: 24483816 DOI: 10.1103/physrevlett.111.268301] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Indexed: 06/03/2023]
Abstract
The long time persistence of mechanical stresses is a generic property of glassy materials. Here we identify the microscopic mechanisms that control internal stresses in highly concentrated suspensions of soft particles brought to rest from steady flow. The persistence of the asymmetric angular distortions which characterize the pair distribution function during flow is at the origin of the internal stresses. Their long time evolution is driven by in-cage rearrangements of the elastic contacts between particles. The trapped macroscopic stress is related to the solvent viscosity, particle elasticity and volume fraction through a universal scaling derived from simulations and experiments.
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Affiliation(s)
- Lavanya Mohan
- Department of Chemical Engineering and Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Roger T Bonnecaze
- Department of Chemical Engineering and Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Michel Cloitre
- Matière Molle et Chimie (UMR 7167, ESPCI-CNRS), ESPCI ParisTech 10 rue Vauquelin, 75005 Paris, France
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78
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Dickinson E. Structure and rheology of colloidal particle gels: insight from computer simulation. Adv Colloid Interface Sci 2013; 199-200:114-27. [PMID: 23916723 DOI: 10.1016/j.cis.2013.07.002] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Revised: 07/08/2013] [Accepted: 07/09/2013] [Indexed: 10/26/2022]
Abstract
A particle gel is a network of aggregated colloidal particles with soft solid-like mechanical properties. Its structural and rheological properties, and the kinetics of its formation, are dependent on the sizes and shapes of the constituent particles, the volume fraction of the particles, and the nature of the interactions between the particles before, during and after gelation. Particle gels may be permanent or transient depending on whether the colloidal forces between the aggregating particles lead to irreversible bonding or weak reversible interactions. With short-range reversible interactions, network formation is typically associated with phase separation or kinetic arrest due to particle crowding. Much existing knowledge has been derived from computer simulations of idealized model systems containing spherical particles interacting with well-defined pair potentials. The status of current progress is reviewed here by summarizing the underlying methodology and key findings from a range of simulation approaches: Monte Carlo, molecular dynamics, Brownian dynamics, Stokesian dynamics, dissipative particle dynamics, multiparticle collision dynamics, and fluid particle dynamics. Then it is described how the technique of Brownian dynamics simulation, in particular, has provided detailed insight into how different kinds of bonding and weak reversible interactions can affect the aggregate fractal structure, the percolation behaviour, and the small-deformation rheological properties of network-forming colloidal systems. A significant ongoing development has been the establishment and testing of efficient algorithms that are able to capture the subtle dynamic structuring effects that arise from effects of interparticle hydrodynamic interactions. This has led to an appreciation recently of the potentially important role of these particle-particle hydrodynamic effects in controlling the evolving morphology of simulated colloidal aggregates and in defining the location of the sol-gel phase boundary.
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79
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Actin assembly factors regulate the gelation kinetics and architecture of F-actin networks. Biophys J 2013; 104:1709-19. [PMID: 23601318 DOI: 10.1016/j.bpj.2013.01.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Revised: 12/27/2012] [Accepted: 01/15/2013] [Indexed: 11/23/2022] Open
Abstract
Dynamic regulation of the actin cytoskeleton is required for diverse cellular processes. Proteins regulating the assembly kinetics of the cytoskeletal biopolymer F-actin are known to impact the architecture of actin cytoskeletal networks in vivo, but the underlying mechanisms are not well understood. Here, we demonstrate that changes to actin assembly kinetics with physiologically relevant proteins profilin and formin (mDia1 and Cdc12) have dramatic consequences on the architecture and gelation kinetics of otherwise biochemically identical cross-linked F-actin networks. Reduced F-actin nucleation rates promote the formation of a sparse network of thick bundles, whereas increased nucleation rates result in a denser network of thinner bundles. Changes to F-actin elongation rates also have marked consequences. At low elongation rates, gelation ceases and a solution of rigid bundles is formed. By contrast, rapid filament elongation accelerates dynamic arrest and promotes gelation with minimal F-actin density. These results are consistent with a recently developed model of how kinetic constraints regulate network architecture and underscore how molecular control of polymer assembly is exploited to modulate cytoskeletal architecture and material properties.
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80
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A Particle Interaction Model for the Simulation of Biological, Cross-Linked Fiber Networks Inspired From flocking Theory. Cell Mol Bioeng 2013. [DOI: 10.1007/s12195-013-0308-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
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81
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Cipelletti L, Brambilla G, Maccarrone S, Caroff S. Simultaneous measurement of the microscopic dynamics and the mesoscopic displacement field in soft systems by speckle imaging. OPTICS EXPRESS 2013; 21:22353-22366. [PMID: 24104125 DOI: 10.1364/oe.21.022353] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The constituents of soft matter systems such as colloidal suspensions, emulsions, polymers, and biological tissues undergo microscopic random motion, due to thermal energy. They may also experience drift motion correlated over mesoscopic or macroscopic length scales, e.g. in response to an internal or applied stress or during flow. We present a new method for measuring simultaneously both the microscopic motion and the mesoscopic or macroscopic drift. The method is based on the analysis of spatio-temporal cross-correlation functions of speckle patterns taken in an imaging configuration. The method is tested on a translating Brownian suspension and a sheared colloidal glass.
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82
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Hou J, Liao LD, Xie YM, Zeng FM, Ji X, Chen B, Li LY, Zhu MX, Yang CX, Qing-Zhao, Chen T, Xu XE, Shen J, Guo MZ, Li EM, Xu LY. DACT2 is a candidate tumor suppressor and prognostic marker in esophageal squamous cell carcinoma. Cancer Prev Res (Phila) 2013; 6:791-800. [PMID: 23803417 DOI: 10.1158/1940-6207.capr-12-0352] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In animals ranging from fish to mice, the function of DACT2 as a negative regulator of the TGF-β/Nodal signal pathway is conserved in evolution, indicating that it might play an important role in human cancer. In this study, we showed that tumors with higher DACT2 protein level were correlated with better differentiation and better survival rate in patients with esophageal squamous cell carcinoma. Restored expression of DACT2 significantly inhibited growth, migration, and invasion of ESCC cells in vitro, and reduced tumorigenicity in vivo. Furthermore, when DACT2 expression was restored, the activity of TGF-β/SMAD2/3 was suppressed via both proteasome and lysosomal degradation pathways, leading to F-actin rearrangement that might depend on the involvement of cofilin and ezrin-redixin-moesin (ERM) proteins. Taken together, we propose here that DACT2 serves as a prognostic marker that reduces tumor cell malignancy by suppressing TGF-β signaling and promotes actin rearrangement in ESCC.
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Affiliation(s)
- Jian Hou
- Institute of Oncologic Pathology, Medical College of Shantou University, Guangdong, China
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83
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Luque T, Melo E, Garreta E, Cortiella J, Nichols J, Farré R, Navajas D. Local micromechanical properties of decellularized lung scaffolds measured with atomic force microscopy. Acta Biomater 2013; 9:6852-9. [PMID: 23470549 DOI: 10.1016/j.actbio.2013.02.044] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Revised: 02/21/2013] [Accepted: 02/26/2013] [Indexed: 01/13/2023]
Abstract
Bioartificial lungs re-engineered from decellularized organ scaffolds are a promising alternative to lung transplantation. Critical features for improving scaffold repopulation depend on the mechanical properties of the cell microenvironment. However, the mechanics of the lung extracellular matrix (ECM) is poorly defined. The local mechanical properties of the ECM were measured in different regions of decellularized rat lung scaffolds with atomic force microscopy. Lungs excised from rats (n=11) were decellularized with sodium dodecyl sulfate (SDS) and cut into ~7μm thick slices. The complex elastic modulus (G(∗)) of lung ECM was measured over a frequency band ranging from 0.1 to 11.45Hz. Measurements were taken in alveolar wall segments, alveolar wall junctions and pleural regions. The storage modulus (G', real part of G(∗)) of alveolar ECM was ~6kPa, showing small changes between wall segments and junctions. Pleural regions were threefold stiffer than alveolar walls. G' of alveolar walls and pleura increased with frequency as a weak power law with exponent 0.05. The loss modulus (G″, imaginary part of G(∗)) was 10-fold lower and showed a frequency dependence similar to that of G' at low frequencies (0.1-1Hz), but increased more markedly at higher frequencies. Local differences in mechanical properties and topology of the parenchymal site could be relevant mechanical cues for regulating the spatial distribution, differentiation and function of lung cells.
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84
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Colombo J, Widmer-Cooper A, Del Gado E. Microscopic picture of cooperative processes in restructuring gel networks. PHYSICAL REVIEW LETTERS 2013; 110:198301. [PMID: 23705744 DOI: 10.1103/physrevlett.110.198301] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Indexed: 06/02/2023]
Abstract
Colloidal gel networks are disordered elastic solids that can form even in extremely dilute particle suspensions. With interaction strengths comparable to the thermal energy, their stress-bearing network can locally restructure via breaking and reforming interparticle bonds. This allows for yielding, self-healing, and adaptive mechanics under deformation. Designing such features requires controlling stress transmission through the complex structure of the gel and this is challenging because the link between local restructuring and overall response of the network is still missing. Here, we use a space resolved analysis of dynamical processes and numerical simulations of a model gel to gain insight into this link. We show that consequences of local bond breaking propagate along the gel network over distances larger than the average mesh size. This provides the missing microscopic explanation for why nonlocal constitutive relations are necessary to rationalize the nontrivial mechanical response of colloidal gels.
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Affiliation(s)
- Jader Colombo
- Department of Civil, Environmental and Geomatic Engineering, ETH Zürich, CH-8093 Zürich, Switzerland
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85
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Falzone TT, Lenz M, Kovar DR, Gardel ML. Assembly kinetics determine the architecture of α-actinin crosslinked F-actin networks. Nat Commun 2012; 3:861. [PMID: 22643888 PMCID: PMC3563296 DOI: 10.1038/ncomms1862] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2011] [Accepted: 04/24/2012] [Indexed: 11/22/2022] Open
Abstract
The actin cytoskeleton is organized into diverse meshworks and bundles that support many aspects of cell physiology. Understanding the self-assembly of these actin-based structures is essential for developing predictive models of cytoskeletal organization. Here we show that the competing kinetics of bundle formation with the onset of dynamic arrest arising from filament entanglements and cross-linking determine the architecture of reconstituted actin networks formed with α-actinin cross-links. Cross-link mediated bundle formation only occurs in dilute solutions of highly mobile actin filaments. As actin polymerization proceeds, filament mobility and bundle formation are arrested concomitantly. By controlling the onset of dynamic arrest, perturbations to actin assembly kinetics dramatically alter the architecture of biochemically identical samples. Thus, the morphology of reconstituted F-actin networks is a kinetically determined structure similar to those formed by physical gels and glasses. These results establish mechanisms controlling the structure and mechanics in diverse semi-flexible biopolymer networks.
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Affiliation(s)
- Tobias T Falzone
- Biophysics Graduate Program, University of Chicago, IL 60637, USA
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86
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Abstract
Mechanical cues affect many important biological processes in metazoan cells, such as migration, proliferation, and differentiation. Such cues are thought to be detected by specialized mechanosensing molecules linked to the cytoskeleton, an intracellular network of protein filaments that provide mechanical rigidity to the cell and drive cellular shape change. The most abundant such filament, actin, forms branched networks nucleated by the actin-related protein (Arp) 2/3 complex that support or induce membrane protrusions and display adaptive behavior in response to compressive forces. Here we show that filamentous actin serves in a mechanosensitive capacity itself, by biasing the location of actin branch nucleation in response to filament bending. Using an in vitro assay to measure branching from curved sections of immobilized actin filaments, we observed preferential branch formation by the Arp2/3 complex on the convex face of the curved filament. To explain this behavior, we propose a fluctuation gating model in which filament binding or branch nucleation by Arp2/3 occur only when a sufficiently large, transient, local curvature fluctuation causes a favorable conformational change in the filament, and we show with Monte Carlo simulations that this model can quantitatively account for our experimental data. We also show how the branching bias can reinforce actin networks in response to compressive forces. These results demonstrate how filament curvature can alter the interaction of cytoskeletal filaments with regulatory proteins, suggesting that direct mechanotransduction by actin may serve as a general mechanism for organizing the cytoskeleton in response to force.
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87
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Dynamic role of cross-linking proteins in actin rheology. Biophys J 2012; 101:1597-603. [PMID: 21961585 DOI: 10.1016/j.bpj.2011.08.033] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2011] [Revised: 07/19/2011] [Accepted: 08/16/2011] [Indexed: 12/22/2022] Open
Abstract
We develop a computational model to compare the relative importance of unbinding and unfolding of actin cross-linking proteins (ACPs) in the dynamic properties of the actin cytoskeleton. We show that in the strain-stiffening regime with typical physiological and experimental strain rates, unbinding events are predominant with negligible unfolding. ACPs unbound by greater forces experience larger displacements, with a tendency to rebind to different filaments. At constant strain, stress relaxes to physiological levels by unbinding only--not unfolding--of ACPs, which is consistent with experiments. Also, rebinding of ACPs dampens full relaxation of stress. When the network is allowed to return to a stress-free state after shear deformation, plastic deformation is observed only with unbinding. These results suggest that despite the possibility of unfolding, unbinding of ACPs is the major determinant for the rheology of the actin network.
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88
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Suei S, Plastino J, Kreplak L. Fascin and VASP synergistically increase the Young’s modulus of actin comet tails. J Struct Biol 2012; 177:40-5. [DOI: 10.1016/j.jsb.2011.11.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Revised: 11/02/2011] [Accepted: 11/05/2011] [Indexed: 01/06/2023]
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89
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Measuring the multi-scale integration of mechanical forces during morphogenesis. Curr Opin Genet Dev 2011; 21:653-63. [PMID: 21930371 DOI: 10.1016/j.gde.2011.08.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Revised: 08/17/2011] [Accepted: 08/17/2011] [Indexed: 12/22/2022]
Abstract
The elaborate changes in morphology of an organism during development are the result of mechanical contributions that are a mixture of those generated locally and those that influence from a distance. We would like to know how chemical and mechanical information is transmitted and transduced, how work is done to achieve robust morphogenesis and why it sometimes fails. We introduce a scheme for separating the influence of two classes of forces. Active intrinsic forces integrate up levels of scale to shape tissues. Counter-currently, extrinsic forces exert influence from higher levels downwards and feed back directly and indirectly upon the intrinsic behaviours. We identify the measurable signatures of different kinds of forces and identify the frontiers where work is most needed.
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