scholarly journals Direct measurement of the lamellipodial protrusive force in a migrating cell

2006 ◽  
Vol 174 (6) ◽  
pp. 767-772 ◽  
Author(s):  
Marcus Prass ◽  
Ken Jacobson ◽  
Alex Mogilner ◽  
Manfred Radmacher
Keyword(s):  
Actin Filaments ◽  
Actin Polymerization ◽  
Leading Edge ◽  
Theoretical Models ◽  
Force Generation ◽  
Direct Measure ◽  
Force Microscopy ◽  
Atomic Force ◽  
Force Velocity ◽  
Atomic Force Microscopy Cantilever

There has been a great deal of interest in the mechanism of lamellipodial protrusion (Pollard, T., and G. Borisy. 2003. Cell. 112:453–465). However, one of this mechanism's endpoints, the force of protrusion, has never been directly measured. We place an atomic force microscopy cantilever in the path of a migrating keratocyte. The deflection of the cantilever, which occurs over a period of ∼10 s, provides a direct measure of the force exerted by the lamellipodial leading edge. Stall forces are consistent with ∼100 polymerizing actin filaments per micrometer of the leading edge, each working as an elastic Brownian ratchet and generating a force of several piconewtons. However, the force-velocity curves obtained from this measurement, in which velocity drops sharply under very small loads, is not sensitive to low loading forces, and finally stalls rapidly at large loads, are not consistent with current theoretical models for the actin polymerization force. Rather, the curves indicate that the protrusive force generation is a complex multiphase process involving actin and adhesion dynamics.

scholarly journals Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

2020 ◽  
Author(s):  
Hongyu Gao ◽  
James Ewen ◽  
Remco Hartkamp ◽  
Martin H. Müser ◽  
Daniele Dini
Keyword(s):  
Surface Coverage ◽  
Leading Edge ◽  
Thermal Dissipation ◽  
Nonequilibrium Molecular Dynamics ◽  
Kinetic Friction ◽  
Surfactant Monolayers ◽  
Force Microscopy ◽  
Sliding Surfaces ◽  
Atomic Force ◽  
Afm Tips

<div>Surfactant molecules, known as organic friction modifiers (OFMs), are added to lubricants to reduce friction and wear between sliding surfaces. In macroscale experiments, friction generally decreases as the coverage of OFM molecules on the sliding surfaces increases. However, recent nanoscale experiments with sharp atomic force microscopy (AFM) tips have shown increasing friction. To elucidate the origin of these opposite trends, we use nonequilibrium molecular dynamics (NEMD) simulations and study kinetic friction between OFM monolayers and an indenting nanoscale asperity. For this purpose, we study various coverages of stearamide OFMs on iron oxide surfaces and silica AFM tips with different radii of curvature. For our small tip radii, the friction coefficient and indentation depth both have a non-monotonic dependence on OFM surface coverage, with maxima occurring at intermediate coverage. This suggests that friction is dominated by plowing. We rationalise the non-monotonic relations through a competition of two effects (confinement and packing density) that varying the surface coverage has on the effective stiffness of the OFM monolayers. We also show that kinetic friction is not very sensitive to the sliding velocity in the range studied, indicating that it originates from instabilities. Indeed, while friction predominately originates from the plowing action of the monolayers by the leading edge of the tip, thermal dissipation is mostly localised in molecules towards the trailing edge of the tip.</div>

3D05 Evaluation of binding between nucleus and actin filaments using atomic force microscopy

2013 ◽  
Vol 2013.25 (0) ◽  
pp. 561-562
Author(s):  
Shinya Chubachi ◽  
Toshiro Anno ◽  
Naoya Sakamoto ◽  
Shinji Deguchi ◽  
Masaaki Sato
Keyword(s):  
Atomic Force Microscopy ◽  
Actin Filaments ◽  
Force Microscopy ◽  
Atomic Force

scholarly journals Analysis of the Actin–Myosin II System in Fish Epidermal Keratocytes: Mechanism of Cell Body Translocation

1997 ◽  
Vol 139 (2) ◽  
pp. 397-415 ◽  
Author(s):  
Tatyana M. Svitkina ◽  
Alexander B. Verkhovsky ◽  
Kyle M. McQuade ◽  
Gary G. Borisy
Keyword(s):  
Cell Body ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Leading Edge ◽  
Time Lapse ◽  
Supramolecular Organization ◽  
Retrograde Flow ◽  
Body Boundary ◽  
Filament Bundles

While the protrusive event of cell locomotion is thought to be driven by actin polymerization, the mechanism of forward translocation of the cell body is unclear. To elucidate the mechanism of cell body translocation, we analyzed the supramolecular organization of the actin–myosin II system and the dynamics of myosin II in fish epidermal keratocytes. In lamellipodia, long actin filaments formed dense networks with numerous free ends in a brushlike manner near the leading edge. Shorter actin filaments often formed T junctions with longer filaments in the brushlike area, suggesting that new filaments could be nucleated at sides of preexisting filaments or linked to them immediately after nucleation. The polarity of actin filaments was almost uniform, with barbed ends forward throughout most of the lamellipodia but mixed in arc-shaped filament bundles at the lamellipodial/cell body boundary. Myosin II formed discrete clusters of bipolar minifilaments in lamellipodia that increased in size and density towards the cell body boundary and colocalized with actin in boundary bundles. Time-lapse observation demonstrated that myosin clusters appeared in the lamellipodia and remained stationary with respect to the substratum in locomoting cells, but they exhibited retrograde flow in cells tethered in epithelioid colonies. Consequently, both in locomoting and stationary cells, myosin clusters approached the cell body boundary, where they became compressed and aligned, resulting in the formation of boundary bundles. In locomoting cells, the compression was associated with forward displacement of myosin features. These data are not consistent with either sarcomeric or polarized transport mechanisms of cell body translocation. We propose that the forward translocation of the cell body and retrograde flow in the lamellipodia are both driven by contraction of an actin–myosin network in the lamellipodial/cell body transition zone.

scholarly journals Detection of atomic force microscopy cantilever displacement with a transmitted electron beam

2016 ◽  
Vol 109 (4) ◽  
pp. 043111 ◽  
Author(s):  
R. Wagner ◽  
T. J. Woehl ◽  
R. R. Keller ◽  
J. P. Killgore
Keyword(s):  
Atomic Force Microscopy ◽  
Electron Beam ◽  
Force Microscopy ◽  
Atomic Force ◽  
Atomic Force Microscopy Cantilever

scholarly journals T cell priming is enhanced by maturation-dependent stiffening of the dendritic cell cortex

2019 ◽  
Author(s):  
Daniel Blumenthal ◽  
Lyndsay Avery ◽  
Vidhi Chandra ◽  
Janis K. Burkhardt
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Actin Polymerization ◽  
Cell Activation ◽  
Cytoskeletal Proteins ◽  
Cell Cortex ◽  
Force Microscopy ◽  
Atomic Force ◽  
Cortical Cytoskeleton

ABSTRACTT cell activation by dendritic cells (DCs) involves forces exerted by the T cell actin cytoskeleton, which are opposed by the cortical cytoskeleton of the interacting APC. During an immune response, DCs undergo a maturation process that optimizes their ability to efficiently prime naïve T cells. Using atomic force microscopy, we find that during maturation, DC cortical stiffness increases via process that involves actin polymerization. Using stimulatory hydrogels and DCs expressing mutant cytoskeletal proteins, we find that increasing stiffness lowers the agonist dose needed for T cell activation. CD4+ T cells exhibit much more profound stiffness-dependency than CD8+ T cells. Finally, stiffness responses are most robust when T cells are stimulated with pMHC rather than anti-CD3ε, consistent with a mechanosensing mechanism involving receptor deformation. Taken together, our data reveal that maturation-associated cytoskeletal changes alter the biophysical properties of DCs, providing mechanical cues that costimulate T cell activation.

Conductive-AFM for Scan Logic Failure Analysis at Advanced Technology Nodes

2016 ◽  
Author(s):  
Chuan Zhang ◽  
Oh Chong Khiam ◽  
Esther P.Y. Chen
Keyword(s):  
Failure Analysis ◽  
Failure Modes ◽  
Leading Edge ◽  
Advanced Technology ◽  
The Novel ◽  
Conductive Atomic Force Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Technology Nodes ◽  
Process Structure

Abstract The increase in complexity of process, structure, and design not only increases the amount of failure analysis (FA) work significantly, but also leads to more complicated failure modes. To meet the need of high success rate and fast throughput FA operation at the leading-edge nodes, novel FA techniques have to be explored and incorporated into the routine FA flow. One of the novel techniques incorporated into the presented scan logic FA flow is the conductive-atomic force microscopy (CAFM) technique. This paper demonstrates CAFM technique as a powerful and efficient solution for scan logic failure analysis at advanced technology nodes. Several failure modes in scan logic FA are used as examples to illustrate how CAFM provides excellent solutions to some of the very challenging FA problems. The gate to active short in nFET devices, resistive contact, and open defect on gate contact are some modes used.

Two conductive mechanisms in LaMnO3 thin film: Adiabatic and nonadiabatic small polaronic hopping

2021 ◽  
pp. 2150310
Author(s):  
Weiyuan Wang ◽  
Jiyu Fan ◽  
Huan Zheng ◽  
Jing Wang ◽  
Hao Liu ◽  
...  
Keyword(s):  
Thin Films ◽  
Theoretical Models ◽  
Magnetic Phase Transitions ◽  
Epitaxial Thin Films ◽  
X Ray Diffraction ◽  
Epitaxial Relationship ◽  
Reciprocal Space Mapping ◽  
Force Microscopy ◽  
Atomic Force ◽  
Out Of Plane

We have presented the structural, surface morphology, magnetic and resistivity data for perovskite LaMnO3 epitaxial thin films which are fabricated on well-oriented (001) LaAlO3 substrates by pulsed laser deposition technique. X-ray diffraction [Formula: see text]–[Formula: see text] linear scans and reciprocal space mapping measurement confirm that the out-of-plane and in-plane epitaxial relationship are LMO(001)/LAO(001) and LMO(110)/LAO(110), respectively. Surface roughness determined by atomic force microscopy was no more than 0.3 nm. In the whole studied temperature range, all films only show a paramagnetic behavior instead of any magnetic phase transitions. Correspondingly, the electron transport behaviors always exhibit an insulting state as the temperature changes from high to low. However, we find that none of theoretical models can individually be used to understand their conductive mechanisms. Further studies indicated that charge carries of high and low temperature region obey adiabatic and nonadiabatic small polaronic hopping mechanisms, respectively. This finding offers new ways of exploiting the abnormal ferromagnetism in LaMnO3 multilayer thin films.

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