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Goyeau L, Livanovičs R, Cēbers A. Dynamics of a flexible ferromagnetic filament in a rotating magnetic field. Phys Rev E 2017; 96:062612. [PMID: 29347291 DOI: 10.1103/physreve.96.062612] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Indexed: 06/07/2023]
Abstract
Flexible magnetic filaments have garnered considerable attention as prospective materials for the creation of different microdevices. We describe a theoretical model of a ferromagnetic filament and derive its equations of motion by variational techniques. The numerical algorithm used to solve the filament dynamics in magnetic fields of different configurations is described. It is found that in a rotating field the filament transitions between synchronous and asynchronous regimes with respect to the rotating field, similarly to a rigid magnetic dipole. The mean angular velocity of the filament is well described by a relation valid for a rigid magnetic dipole with quantitative differences attributable to the flexibility of the filament.
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Affiliation(s)
- L Goyeau
- PHITEM department, University of Grenoble Alpes, 230 rue de la Physique, 38400 Saint-Martin-d'Heres, France
| | - R Livanovičs
- MMML Laboratory, Department of Physics, University of Latvia, Zeļļu-23, Rīga LV-1002, Latvia
| | - A Cēbers
- MMML Laboratory, Department of Physics, University of Latvia, Zeļļu-23, Rīga LV-1002, Latvia
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2
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Mazuel F, Mathieu S, Di Corato R, Bacri JC, Meylheuc T, Pellegrino T, Reffay M, Wilhelm C. Forced- and Self-Rotation of Magnetic Nanorods Assembly at the Cell Membrane: A Biomagnetic Torsion Pendulum. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2017; 13:1701274. [PMID: 28660724 DOI: 10.1002/smll.201701274] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Revised: 05/10/2017] [Indexed: 06/07/2023]
Abstract
In order to provide insight into how anisotropic nano-objects interact with living cell membranes, and possibly self-assemble, magnetic nanorods with an average size of around 100 nm × 1 µm are designed by assembling iron oxide nanocubes within a polymeric matrix under a magnetic field. The nano-bio interface at the cell membrane under the influence of a rotating magnetic field is then explored. A complex structuration of the nanorods intertwined with the membranes is observed. Unexpectedly, after a magnetic rotating stimulation, the resulting macrorods are able to rotate freely for multiple rotations, revealing the creation of a biomagnetic torsion pendulum.
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Affiliation(s)
- François Mazuel
- Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057, CNRS and Université Paris Diderot, Paris Cedex 05, 75205, France
| | - Samuel Mathieu
- Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057, CNRS and Université Paris Diderot, Paris Cedex 05, 75205, France
| | - Riccardo Di Corato
- Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057, CNRS and Université Paris Diderot, Paris Cedex 05, 75205, France
- Dipartimento di Matematica e Fisica "Ennio De Giorgi", Università del Salento, Via Arnesano, Lecce, 73100, Italy
| | - Jean-Claude Bacri
- Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057, CNRS and Université Paris Diderot, Paris Cedex 05, 75205, France
| | - Thierry Meylheuc
- Micalis Institute INRA, AgroParisTech, Université Paris-Saclay, 78350, Jouy-en-Josas, France
| | | | - Myriam Reffay
- Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057, CNRS and Université Paris Diderot, Paris Cedex 05, 75205, France
| | - Claire Wilhelm
- Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057, CNRS and Université Paris Diderot, Paris Cedex 05, 75205, France
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Norregaard K, Metzler R, Ritter CM, Berg-Sørensen K, Oddershede LB. Manipulation and Motion of Organelles and Single Molecules in Living Cells. Chem Rev 2017; 117:4342-4375. [PMID: 28156096 DOI: 10.1021/acs.chemrev.6b00638] [Citation(s) in RCA: 168] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The biomolecule is among the most important building blocks of biological systems, and a full understanding of its function forms the scaffold for describing the mechanisms of higher order structures as organelles and cells. Force is a fundamental regulatory mechanism of biomolecular interactions driving many cellular processes. The forces on a molecular scale are exactly in the range that can be manipulated and probed with single molecule force spectroscopy. The natural environment of a biomolecule is inside a living cell, hence, this is the most relevant environment for probing their function. In vivo studies are, however, challenged by the complexity of the cell. In this review, we start with presenting relevant theoretical tools for analyzing single molecule data obtained in intracellular environments followed by a description of state-of-the art visualization techniques. The most commonly used force spectroscopy techniques, namely optical tweezers, magnetic tweezers, and atomic force microscopy, are described in detail, and their strength and limitations related to in vivo experiments are discussed. Finally, recent exciting discoveries within the field of in vivo manipulation and dynamics of single molecule and organelles are reviewed.
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Affiliation(s)
- Kamilla Norregaard
- Cluster for Molecular Imaging, Department of Biomedical Science and Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen , 2200 Copenhagen, Denmark
| | - Ralf Metzler
- Institute for Physics & Astronomy, University of Potsdam , 14476 Potsdam-Golm, Germany
| | - Christine M Ritter
- Niels Bohr Institute, University of Copenhagen , 2100 Copenhagen, Denmark
| | | | - Lene B Oddershede
- Niels Bohr Institute, University of Copenhagen , 2100 Copenhagen, Denmark
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Alieva IB, Kireev I, Garanina AS, Alyabyeva N, Ruyter A, Strelkova OS, Zhironkina OA, Cherepaninets VD, Majouga AG, Davydov VA, Khabashesku VN, Agafonov V, Uzbekov RE. Magnetocontrollability of Fe7C3@C superparamagnetic nanoparticles in living cells. J Nanobiotechnology 2016; 14:67. [PMID: 27576904 PMCID: PMC5006615 DOI: 10.1186/s12951-016-0219-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 08/18/2016] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND A new type of superparamagnetic nanoparticles with chemical formula Fe7C3@C (MNPs) showed higher value of magnetization compared to traditionally used iron oxide-based nanoparticles as was shown in our previous studies. The in vitro biocompatibility tests demonstrated that the MNPs display high efficiency of cellular uptake and do not affect cyto-physiological parameters of cultured cells. These MNPs display effective magnetocontrollability in homogeneous liquids but their behavior in cytoplasm of living cells under the effect of magnetic field was not carefully analyzed yet. RESULTS In this work we investigated the magnetocontrollability of MNPs interacting with living cells in permanent magnetic field. It has been shown that cells were capable of capturing MNPs by upper part of the cell membrane, and from the surface of the cultivation substrate during motion process. Immunofluorescence studies using intracellular endosomal membrane marker showed that MNP agglomerates can be either located in endosomes or lying free in the cytoplasm. When attached cells were exposed to a magnetic field up to 0.15 T, the MNPs acquired magnetic moment and the displacement of incorporated MNP agglomerates in the direction of the magnet was observed. Weakly attached or non-attached cells, such as cells in mitosis or after cytoskeleton damaging treatments moved towards the magnet. During long time cultivation of cells with MNPs in a magnetic field gradual clearing of cells from MNPs was observed. It was the result of removing MNPs from the surface of the cell agglomerates discarded in the process of exocytosis. CONCLUSIONS Our data allow us to conclude for the first time that the magnetic properties of the MNPs are sufficient for successful manipulation with MNP agglomerates both at the intracellular level, and within the whole cell. The structure of the outer shells of the MNPs allows firmly associate different types of biological molecules with them. This creates prospects for the use of such complexes for targeted delivery and selective removal of selected biological molecules from living cells.
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Affiliation(s)
- Irina B. Alieva
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia 119992
| | - Igor Kireev
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia 119992
- Biology Faculty, Moscow State University, Moscow, Russia 119992
| | | | - Natalia Alyabyeva
- GREMAN, UMR CNRS 7347, Université François Rabelais, 37200 Tours, France
| | - Antoine Ruyter
- GREMAN, UMR CNRS 7347, Université François Rabelais, 37200 Tours, France
| | - Olga S. Strelkova
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia 119992
| | - Oxana A. Zhironkina
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia 119992
| | - Varvara D. Cherepaninets
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia 119992
| | - Alexander G. Majouga
- Chemistry Faculty, Moscow State University, Moscow, Russia 119992
- MISiS, Leninskiy prospekt 2, Moscow, Russia 119049
| | - Valery A. Davydov
- Institute of High Pressure Physics RAS, Troitsk, Moscow region Russia 142190
| | | | - Viatcheslav Agafonov
- GREMAN, UMR CNRS 7347, Université François Rabelais, 37200 Tours, France
- MISiS, Leninskiy prospekt 2, Moscow, Russia 119049
| | - Rustem E. Uzbekov
- Laboratoire Biologie Cellulaire et Microscopie Electronique, Faculté de Médecine, Université François Rabelais, 37032 Tours, France
- Faculty of Bioengineering and Bioinformatics, Moscow State University, Moscow, Russia 119992
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Duncan GA, Fairbrother DH, Bevan MA. Diffusing colloidal probes of cell surfaces. SOFT MATTER 2016; 12:4731-4738. [PMID: 27117575 DOI: 10.1039/c5sm02637g] [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
Measurements and analyses are reported to quantify dynamic and equilibrium interactions between colloidal particles and live cell surfaces using dark field video microscopy. Two-dimensional trajectories of micron-sized polyethylene glycol (PEG)-coated silica colloids relative to adherent epithelial breast cancer cell perimeters are determined allowing measurement of position dependent diffusivities and interaction potentials. PEG was chosen as the material system of interest to assess non-specific interactions with cell surfaces and establishes a basis for investigation of specific interactions in future studies. Analysis of measured potential energies on cell surfaces reveals the spatial dependence in cell topography. With the measured cell topography and models for particle-cell surface hydrodynamic interactions, excellent agreement is obtained between theoretical and measured colloidal transport on cell surfaces. Quantitative analyses of association lifetimes showed that PEG coatings act to stabilize colloids above the cell surface through net repulsive, steric interactions. Our results demonstrate a self-consistent analysis of diffusing colloidal probe interactions due to conservative and non-conservative forces to characterize biophysical cell surface properties.
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Brasovs A, Cīmurs J, Ērglis K, Zeltins A, Berret JF, Cēbers A. Magnetic microrods as a tool for microrheology. SOFT MATTER 2015; 11:2563-2569. [PMID: 25692605 DOI: 10.1039/c4sm02454k] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Dynamics of superparamagnetic rods in crossed constant and alternating magnetic fields as a function of field frequency are studied and it is shown that above the critical value of the amplitude of the alternating field the rod oscillates around the direction of the alternating field. The fit of the experimentally measured time dependence of the mean orientation angle of the rod allows one to determine the ratio of magnetic and viscous torques which act on the rod. The protocol of microrheological measurements consists of recording the dynamics of the orientation of the rod when the magnetic field is applied at an angle to the rod and observing its relaxation due to the accumulated elastic energy after the field is switched off. The microrheological data obtained are in reasonable agreement with the macrorheological measurements.
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Affiliation(s)
- Artis Brasovs
- Faculty of Physics and Mathematics, University of Latvia, Zeļļu-8, Rīga, LV-1021, Latvia.
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Cugliandolo LF, Déjardin PM, Lozano GS, van Wijland F. Stochastic dynamics of collective modes for Brownian dipoles. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:032139. [PMID: 25871086 DOI: 10.1103/physreve.91.032139] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Indexed: 06/04/2023]
Abstract
The individual motion of a colloidal particle is described by an overdamped Langevin equation. When rotational degrees of freedom are relevant, these are described by a corresponding Langevin process. Our purpose is to show that the microscopic local density of colloids, in terms of a space and rotation state, also evolves according to a Langevin equation. The latter can then be used as the starting point of a variety of approaches, ranging from dynamical density functional theory to mode-coupling approximations.
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Affiliation(s)
- Leticia F Cugliandolo
- Laboratoire de Physique Théorique et Hautes Énergies, Sorbonne Universités, Université Pierre et Marie Curie-Paris 6, and UMR 7589 CNRS/P6, 4 place Jussieu, 75252 Paris cedex 05, France
| | - Pierre-Michel Déjardin
- Laboratoire de Mathématiques et de Physique, Université de Perpignan Via Domitia, 52 avenue Paul Alduy, 66860 Perpignan cedex, France
| | - Gustavo S Lozano
- Departmento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires Ciudad Universitaria, Pabellon I, 1428 Buenos Aires, Argentina
| | - Frédéric van Wijland
- Laboratoire Matière et Systèmes Complexes, UMR 7057 CNRS/P7, Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris cedex 13, France
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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Lateral motion and bending of microtubules studied with a new single-filament tracking routine in living cells. Biophys J 2015; 106:2625-35. [PMID: 24940780 DOI: 10.1016/j.bpj.2014.04.046] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 04/07/2014] [Accepted: 04/18/2014] [Indexed: 12/24/2022] Open
Abstract
The cytoskeleton is involved in numerous cellular processes such as migration, division, and contraction and provides the tracks for transport driven by molecular motors. Therefore, it is very important to quantify the mechanical behavior of the cytoskeletal filaments to get a better insight into cell mechanics and organization. It has been demonstrated that relevant mechanical properties of microtubules can be extracted from the analysis of their motion and shape fluctuations. However, tracking individual filaments in living cells is extremely complex due, for example, to the high and heterogeneous background. We introduce a believed new tracking algorithm that allows recovering the coordinates of fluorescent microtubules with ∼9 nm precision in in vitro conditions. To illustrate potential applications of this algorithm, we studied the curvature distributions of fluorescent microtubules in living cells. By performing a Fourier analysis of the microtubule shapes, we found that the curvatures followed a thermal-like distribution as previously reported with an effective persistence length of ∼20 μm, a value significantly smaller than that measured in vitro. We also verified that the microtubule-associated protein XTP or the depolymerization of the actin network do not affect this value; however, the disruption of intermediate filaments decreased the persistence length. Also, we recovered trajectories of microtubule segments in actin or intermediate filament-depleted cells, and observed a significant increase of their motion with respect to untreated cells showing that these filaments contribute to the overall organization of the microtubule network. Moreover, the analysis of trajectories of microtubule segments in untreated cells showed that these filaments presented a slower but more directional motion in the cortex with respect to the perinuclear region, and suggests that the tracking routine would allow mapping the microtubule dynamical organization in cells.
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9
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Maloney JM, Lehnhardt E, Long AF, Van Vliet KJ. Mechanical fluidity of fully suspended biological cells. Biophys J 2014; 105:1767-77. [PMID: 24138852 DOI: 10.1016/j.bpj.2013.08.040] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Revised: 08/01/2013] [Accepted: 08/26/2013] [Indexed: 11/16/2022] Open
Abstract
Mechanical characteristics of single biological cells are used to identify and possibly leverage interesting differences among cells or cell populations. Fluidity-hysteresivity normalized to the extremes of an elastic solid or a viscous liquid-can be extracted from, and compared among, multiple rheological measurements of cells: creep compliance versus time, complex modulus versus frequency, and phase lag versus frequency. With multiple strategies available for acquisition of this nondimensional property, fluidity may serve as a useful and robust parameter for distinguishing cell populations, and for understanding the physical origins of deformability in soft matter. Here, for three disparate eukaryotic cell types deformed in the suspended state via optical stretching, we examine the dependence of fluidity on chemical and environmental influences at a timescale of ∼1 s. We find that fluidity estimates are consistent in the time and frequency domains under a structural damping (power-law or fractional-derivative) model, but not under an equivalent-complexity, lumped-component (spring-dashpot) model; the latter predicts spurious time constants. Although fluidity is suppressed by chemical cross-linking, we find that ATP depletion in the cell does not measurably alter the parameter, and we thus conclude that active ATP-driven events are not a crucial enabler of fluidity during linear viscoelastic deformation of a suspended cell. Finally, by using the capacity of optical stretching to produce near-instantaneous increases in cell temperature, we establish that fluidity increases with temperature-now measured in a fully suspended, sortable cell without the complicating factor of cell-substratum adhesion.
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Affiliation(s)
- John M Maloney
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts
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Otero MG, Alloatti M, Cromberg LE, Almenar-Queralt A, Encalada SE, Pozo Devoto VM, Bruno L, Goldstein LSB, Falzone TL. Fast axonal transport of the proteasome complex depends on membrane interaction and molecular motor function. J Cell Sci 2014; 127:1537-49. [PMID: 24522182 DOI: 10.1242/jcs.140780] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Protein degradation by the ubiquitin-proteasome system in neurons depends on the correct delivery of the proteasome complex. In neurodegenerative diseases, aggregation and accumulation of proteins in axons link transport defects with degradation impairments; however, the transport properties of proteasomes remain unknown. Here, using in vivo experiments, we reveal the fast anterograde transport of assembled and functional 26S proteasome complexes. A high-resolution tracking system to follow fluorescent proteasomes revealed three types of motion: actively driven proteasome axonal transport, diffusive behavior in a viscoelastic axonema and proteasome-confined motion. We show that active proteasome transport depends on motor function because knockdown of the KIF5B motor subunit resulted in impairment of the anterograde proteasome flux and the density of segmental velocities. Finally, we reveal that neuronal proteasomes interact with intracellular membranes and identify the coordinated transport of fluorescent proteasomes with synaptic precursor vesicles, Golgi-derived vesicles, lysosomes and mitochondria. Taken together, our results reveal fast axonal transport as a new mechanism of proteasome delivery that depends on membrane cargo 'hitch-hiking' and the function of molecular motors. We further hypothesize that defects in proteasome transport could promote abnormal protein clearance in neurodegenerative diseases.
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Affiliation(s)
- Maria G Otero
- Instituto de Biología Celular y Neurociencias (UBA-CONICET), Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires CP 1121, Argentina
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11
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Aubertin K, Bonneau S, Silva AKA, Bacri JC, Gallet F, Wilhelm C. Impact of photosensitizers activation on intracellular trafficking and viscosity. PLoS One 2013; 8:e84850. [PMID: 24386423 PMCID: PMC3874004 DOI: 10.1371/journal.pone.0084850] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Accepted: 11/19/2013] [Indexed: 11/19/2022] Open
Abstract
The intracellular microenvironment is essential for the efficiency of photo-induced therapies, as short-lived reactive oxygen species generated must diffuse through their intracellular surrounding medium to reach their cellular target. Here, by combining measurements of local cytoplasmic dissipation and active trafficking, we found that photosensitizers activation induced small changes in surrounding viscosity but a massive decrease in diffusion. These effects are the signature of a return to thermodynamic equilibrium of the system after photo-activation and correlated with depolymerization of the microtubule network, as shown in a reconstituted system. These mechanical measurements were performed with two intracellular photosensitizing chlorins having similar quantum yield of singlet oxygen production but different intracellular localizations (cytoplasmic for mTHPC, endosomal for TPCS2a). These two agents demonstrated different intracellular impact.
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Affiliation(s)
- Kelly Aubertin
- Laboratoire Matière et Systèmes Complexes (MSC), CNRS and Université Paris Diderot, Paris, France
| | - Stéphanie Bonneau
- Laboratoire Jean Perrin-CNRS, Université Pierre et Marie Curie, Paris 6, Paris, France
| | - Amanda K. A. Silva
- Laboratoire Matière et Systèmes Complexes (MSC), CNRS and Université Paris Diderot, Paris, France
| | - Jean-Claude Bacri
- Laboratoire Matière et Systèmes Complexes (MSC), CNRS and Université Paris Diderot, Paris, France
| | - François Gallet
- Laboratoire Matière et Systèmes Complexes (MSC), CNRS and Université Paris Diderot, Paris, France
| | - Claire Wilhelm
- Laboratoire Matière et Systèmes Complexes (MSC), CNRS and Université Paris Diderot, Paris, France
- * E-mail:
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12
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When size does matter: organelle size influences the properties of transport mediated by molecular motors. Biochim Biophys Acta Gen Subj 2013; 1830:5095-103. [DOI: 10.1016/j.bbagen.2013.06.043] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 05/07/2013] [Accepted: 06/29/2013] [Indexed: 12/18/2022]
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13
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Harrer CJ, Winter D, Horbach J, Fuchs M, Voigtmann T. Force-induced diffusion in microrheology. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:464105. [PMID: 23114229 DOI: 10.1088/0953-8984/24/46/464105] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We investigate the force-induced diffusive motion of a tracer particle inside a glass-forming suspension when a strong external force is applied to the probe (active nonlinear microrheology). A schematic model of mode-coupling theory introduced recently is extended to describe the transient dynamics of the probe particle, and used to analyze recent molecular-dynamics simulation data. The model describes non-trivial transient displacements of the probe before a steady-state velocity is reached. The external force also induces diffusive motion in the direction perpendicular to its axis. We address the relation between the transverse diffusion coefficient D(perpendicular) and the force-dependent nonlinear friction coefficient ζ. Non-diffusive fluctuations in the direction of the force are seen at long times in the MD simulation, while the model describes cross-over to long-time diffusion.
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Affiliation(s)
- Ch J Harrer
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
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