Soft Lubrication

Skotheim, Jan M.; Mahadevan, L.

doi:10.1103/physrevlett.92.245509

Cited by 122 publications

(173 citation statements)

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“…This formalism accounts for the dynamics of cytoplasm by including the movement of liquid through a soft porous mesh. It has been previously applied in various forms to understand aspects of the mechanics of whole cells [9,10], and extracellular matrix gels such as collagen [11], and cartilage [12,13]. Here, we review its implications for motility of single cells that involves shape change, such as leading edge protrusion or cleavage furrow invagination.…”

Section: A Minimal Microstructural Model For Cytoplasm: Poroelasticitymentioning

confidence: 99%

“…Scale bar = 10 microns. From [12]. Protrusion of the leading edge (top row) is known to require actin polymerization.…”

Section: Figure 2 Towards a Microstructural Model For Cytoplasmmentioning

confidence: 99%

“…To understand the theory in a minimal setting, we consider a thought experiment in which a load is suddenly applied onto a very long, confined, hydrated, soft, porous gel via a porous plunger (figure 3), first introduced in [12] to explain and interpret some observations of cell blebbing. In a cellular situation, the porous plunger could, for example, represent the plasma membrane, and it could be depressed by a hypertonic shock, or contractile force.…”

Section: A Minimal Microstructural Model For Cytoplasm: Poroelasticitymentioning

confidence: 99%

“…We were drawn to consider poroelasticity by analysis of blebbing [12], a dramatic type of motility that many animal cells display when they divide [30,31] or undergo apoptosis [32]. Blebbing is typically a cyclic phenomenon where a bleb nucleates, expands, and contracts over 1-3 minutes without moving laterally ( figure 5 [33,34]).…”

Section: Exhibit 1: Blebbing As a Window Into Cell Hydraulicsmentioning

confidence: 99%

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Implications of a poroelastic cytoplasm for the dynamics of animal cell shape

Mitchison

Charras

Mahadevan

2008

Seminars in Cell & Developmental Biology

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Two views have dominated recent discussions of the physical basis of cell shape change during migration and division of animal cells: the cytoplasm can be modeled as a viscoelastic continuum, and the forces that change its shape are generated only by actin polymerization and actomyosin contractility in the cell cortex. Here, we question both views: we suggest that the cytoplasm is better described as poroelastic, and that hydrodynamic forces may be generally important for its shape dynamics. In the poroelastic view, the cytoplasm consists of a porous, elastic solid (cytoskeleton, organelles, ribosomes) penetrated by an interstitial fluid (cytosol) that moves through the pores in response to pressure gradients. If the pore size is small (30-60nm), as has been observed in some cells, pressure does not globally equilibrate on time and length scales relevant to cell motility. Pressure differences across the plasma membrane drive blebbing, and potentially other type of protrusive motility. In the poroelastic view, these pressures can be higher in one part of a cell than another, and can thus cause local shape change. Local pressure transients could be generated by actomyosin contractility, or by local activation of osmogenic ion transporters in the plasma membrane. We propose that local activation of Na+/H+ antiporters (NHE1) at the front of migrating cells promotes local swelling there to help drive protrusive motility, acting in combination with actin polymerization. Local shrinking at the equator of dividing cells may similarly help drive invagination during cytokinesis, acting in combination with actomyosin contractility. Testing these hypotheses is not easy, as water is a difficult analyte to track, and will require a joint effort of the cytoskeleton and ion physiology communities.

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Section: A Minimal Microstructural Model For Cytoplasm: Poroelasticitymentioning

confidence: 99%

“…Scale bar = 10 microns. From [12]. Protrusion of the leading edge (top row) is known to require actin polymerization.…”

Section: Figure 2 Towards a Microstructural Model For Cytoplasmmentioning

confidence: 99%

Section: A Minimal Microstructural Model For Cytoplasm: Poroelasticitymentioning

confidence: 99%

Section: Exhibit 1: Blebbing As a Window Into Cell Hydraulicsmentioning

confidence: 99%

See 2 more Smart Citations

Implications of a poroelastic cytoplasm for the dynamics of animal cell shape

Mitchison

Charras

Mahadevan

2008

Seminars in Cell & Developmental Biology

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143

113

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“…For motion parallel to the interface (Figs. 1c and d), surface deformation leads to a lift force on the sphere, perpendicular to its direction of motion and directed away from the interface [7,8], reminiscent of the lift force responsible for the migration of deformable bodies such as droplets [9], vesicles [10,11] and polymers [12] away from boundaries. These effects are due to the nonlinear (geometric) coupling between the moving sphere and the deformable interface, and they vanish when the interfaces do not deform.…”

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confidence: 99%

Soft Swimming: Exploiting Deformable Interfaces for Low Reynolds Number Locomotion

Trouilloud

Hosoi

et al. 2008

Phys. Rev. Lett.

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Reciprocal movement cannot be used for locomotion at low-Reynolds number in an infinite fluid or near a rigid surface. Here we show that this limitation is relaxed for a body performing reciprocal motions near a deformable interface. Using physical arguments and scaling relationships, we show that the nonlinearities arising from reciprocal flow-induced interfacial deformation rectify the periodic motion of the swimmer, leading to locomotion. Such a strategy can be used to move toward, away from, and parallel to any deformable interface as long as the length scales involved are smaller than intrinsic scales, which we identify. A macro-scale experiment of flapping motion near a free surface illustrates this new result.Swimming microorganisms inhabit a world quite different from the one we experience. Their motion through the surrounding fluid occurs at very low Reynolds numbers (Re), a fact with two important consequences: (a) the only physical force available to produce thrust is drag; (b) since the fluid equations (Stokes equations) are linear and time-reversible, swimming motions symmetric with respect to time reversal (reciprocal motion) cannot be used for locomotion (the scallop theorem [1]). Biological swimmers, such as bacteria and spermatozoa, overcome these two limitations by exploiting the anisotropic drag of slender filaments such as flagella and cilia, and actuating these filaments in a wave-like fashion [2,3].Motivated by the recent development of artificial swimmers [4], we pose here the following general question: are there any new low-Re swimming methods remaining to be discovered? In particular, can some simple reciprocal movements produce locomotion, thereby apparently violating the constraints of the scallop theorem?In this paper, we propose a new method for locomotion without inertia. Using theory and experiments, we show that a body performing a reciprocal movement is able to move near a soft interface: physically, the deformation of the interface provides the geometric nonlinearities necessary to escape the constraints of the scallop theorem. This strategy, which is relevant for sufficiently small systems, also implies that the time-reversible component of all swimmers (including biological organisms) can generate non-trivial flows and propulsive forces near soft interfaces.The physical picture for soft swimming arises from the asymmetries between different modes of motion near deformable interfaces, and can be illustrated by considering the motion of a rigid sphere slowly translating below a free surface ( Fig.

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‘Oral’ Tribology

Stokes

2012

Food Oral Processing

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Soft Lubrication

Cited by 122 publications

References 11 publications

Implications of a poroelastic cytoplasm for the dynamics of animal cell shape

Implications of a poroelastic cytoplasm for the dynamics of animal cell shape

Soft Swimming: Exploiting Deformable Interfaces for Low Reynolds Number Locomotion

‘Oral’ Tribology

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