On the Density and Structure Formation in Gels and Clusters of Colloidal Rods and Fibers

Philipse, Albert P.; Wierenga, Anieke M.

doi:10.1021/la9703757

Cited by 112 publications

(95 citation statements)

References 25 publications

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“…The maximum filament length observed in fibers was only 1.5 m, and the average length was 0.67 m. Thus, to a first approximation, the filaments can be considered rigid or at least relatively inflexible. The decrease in packing density in fibers associated with MSP filament elongation is consistent with the packing behavior of rigid (15)(16)(17) or semiflexible (18) rods, in which the maximum packing density decreases with increasing aspect ratio (length/diameter), so that longer rods pack less densely than shorter ones (15)(16)(17).…”

Section: Electron Tomography Indicates That Msp Filaments Pack Like Rsupporting

confidence: 73%

“…The organization of MSP filaments in fibers resembles that produced by random packing of rigid rods on both macro-and microscales (15)(16)(17)(18). The MSP filament persistence length, measured from electron micrographs of negatively stained filaments assembled from purified protein, was Ϸ9 m (SI Text).…”

Section: Electron Tomography Indicates That Msp Filaments Pack Like Rmentioning

confidence: 99%

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The role of filament-packing dynamics in powering amoeboid cell motility

Liu¹,

Vanderlinde²,

et al. 2008

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

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Although several models have been proposed to account for how cytoskeleton polymerization drives protrusion in cell motility, the precise mechanism remains controversial. Here, we show that, in addition to force exerted directly against the membrane by growing filaments, the way elongating filaments pack also contributes to protrusion by generating an expansion of the cytoskeleton gel. Tomography shows that filament packing in the major sperm protein (MSP) -based nematode sperm-motility machinery resembles that observed with rigid rods. Maximum rod-packing density decreases dramatically as the rods lengthen. Therefore, as filaments elongate, the cytoskeleton gel expands to accommodate their packing less densely. This volume expansion combines with polymerization to drive protrusion. Consistent with this hypothesis, an engineered MSP mutant that generates shorter filaments shows higher filament-packing density and slower movement.leading edge ͉ major sperm protein ͉ protrusion T he crawling movement of eukaryotic cells depends on directed lamellipod protrusion, a process linked to actin filament assembly that expands the cytoskeleton gel at the cell's leading edge (1-5). Although several models have been proposed to account for how polymerization drives protrusion, the precise mechanism remains controversial (6). The Brownian ratchet model (4, 6, 7), for example, proposes that addition of new subunits to cytoskeleton filaments in contact with the membrane generates a protrusive force that drives the membrane forward. However, in addition to pushing against the membrane, filaments can also push against one another. Here, we use the motile machinery of amoeboid sperm of Ascaris suum to illustrate how the packing of elongating filaments can make a complementary contribution to protrusion by expanding the cytoskeleton gel.Ascaris sperm motility is remarkably similar to that of other crawling cells and involves extension of a filament-packed lamellipod that attaches to the substrate and pulls the trailing cell body forward (8), even though the motility of these cells is based on the assembly dynamics of filaments formed from major sperm protein (MSP) rather than actin. In nematode sperm, lamellipodial protrusion is powered by assembly of MSP filament networks along the leading-edge membrane (8) that is closely analogous to how actin assembly powers protrusion in other cells (1-4). MSP motility is based on a small number of proteins, and this simplicity offers advantages in studying the basic principles of amoeboid motility (8-10). Moreover, leading-edge protrusion can be reconstituted in sperm extracts, where vesicles derived from the leading edge of the lamellipod trigger assembly of a cylindrical meshwork of MSP filaments, called fibers, that exhibit the same organization and dynamics as the MSP cytoskeleton in sperm (11). As each fiber elongates, it pushes its vesicle forward [supporting information (SI) Movie S1] in the same way that localized assembly of the cytoskeleton pushes the leading edge ahead in crawling ...

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Section: Electron Tomography Indicates That Msp Filaments Pack Like Rsupporting

confidence: 73%

Section: Electron Tomography Indicates That Msp Filaments Pack Like Rmentioning

confidence: 99%

The role of filament-packing dynamics in powering amoeboid cell motility

Liu¹,

Vanderlinde²,

et al. 2008

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

View full text Add to dashboard Cite

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“…There are three possible scenarios: (i) the formation of bundles of average size N ; (ii) chain formation, where N aligned nanotubes overlap minimally at their ends; and (iii) the formation of a heterogeneous network of fractal aggregates. 57,62,67 In our system, all three effects presumably exist. Bundle formation reduces the aspect ratio to λ ′ = λ/ √ N in Eq.…”

Section: B Scaling Electronic Type and Film Durabilitymentioning

confidence: 87%

“…The packing of such rods can be modeled by assuming independent and pair-wise additive contacts. 56,57 This works for large-aspect-ratio rods (> 15), colloidal rods, and macroscopic (> 1 cm) fibers. 56 The orientational average of the excluded volume of a pair of randomly oriented rods gives the so-called 'random-contact' equation of state…”

Section: B Scaling Electronic Type and Film Durabilitymentioning

confidence: 99%

Empirical evaluation of attractive van der Waals potentials for type-purified single-walled carbon nanotubes

et al. 2012

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Van der Waals forces play a critical role in the structure and stability of single-wall carbon nanotube (SWCNT) materials. Thin films assembled from SWCNTs purified by electronic type show particular promise for flexible electronics applications, but mechanical durability remains an unresolved issue. Using transition resonances determined from spectroscopic measurements of typepurified SWCNTs deposited on quartz, coupled with analogous spectroscopic characterization of polydimethylsiloxane (PDMS) substrates, we use the Lifshitz theory of van der Waals dispersion interactions developed by Rajter and co-workers [R. F. Rajter et. al., Phys. Rev. B 76, 045417 (2007)] to examine the influence of electronic type on van der Waals contact potentials in polymer supported nanotube networks. Our results suggest a significantly stronger nanotube-nanotube and nanotube-polymer attraction for the semiconducting SWCNT fractions, consistent with recent measurements of the electronic durability of flexible transparent SWCNT coatings.PACS numbers: 61.48. De, 78.67.Ch, 82.35.Np, 78.20.Bh 2 I. INTRODUCTIONVan der Waals (vdW) forces play a significant role in the structural stability of matter across a broad range of chemistry, physics, and biology. 1-6 They also play a particularly important role in nanotechnology, where they dominate the short-range attraction between nanoparticles and can hinder their dispersion and manipulation. [7][8][9][10][11] For particles lacking a permanent dipole moment, vdW dispersion forces arise solely from small fluctuations in the electromagnetic field -or more precisely, the dielectric permittivity -across the space between the particles, 12,13 which is dominated by the zero-point energy of quantum vacuum fluctuations. The quantum-field nature of such a mundane, ubiquitous and sometimes macroscopic force is quite remarkable, if on occasion not fully appreciated.Single-wall carbon nanotubes (SWCNTs) are nanometer thick tubes of graphene 100 nm to 100 µm in length. They can be either metallic or semiconducting, depending on the chiral vector (n, m) that characterizes the symmetry of rolling a 2D graphene sheet into a hollow tube. 14 They are one of the most studied materials within the realm of modern nanotechnology, with exceptional physical properties that herald the possibility of significant technological potential. 15 The importance of vdW forces in SWCNT materials cannot be overstated. The high aspect ratio and strong anisotropy create potential wells thousands of k B T in depth, but SWCNTs have yet to realize their full potential as mechanical reinforcing agents. This is primarily due to the mechanical failure of interfacial contacts, which are largely governed by vdW forces. Although chemical crosslinking can help mitigate such effects, this often occurs at the expense of the intrinsic SWCNT properties of interest, 16 which can limit the potential impact of applications.Raw nanotube materials typically contain a broad distribution of lengths and a mixture of the two distinct electronic species...

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“…An example of such a shape effect is the formation of spacefilling gels of randomly oriented rodlike particles at very low solid contents. 1 This space-filling efficiency is exploited by biological cells, which possess a tough elastic framework of rodlike macromolecules, called the cytoskeleton, which provides structural stability while also providing sufficient porosity to allow transport of proteins and organelles within the cell cytoplasm. Another striking shape anisotropy effect is the large viscosity of rod 2 and plate 3 suspensions at very low volume fractions, which makes anisometric particles and macromolecules widely applied additives to control the flow properties of industrial and commercial particle suspensions.…”

Section: Introductionmentioning

confidence: 99%

Rotational dynamics of colloidal tracer spheres in suspensions of charged rigid rods

Koenderink

Aarts

Philipse

2003

The Journal of Chemical Physics

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The short-time rotational dynamics of colloidal silica tracer spheres in suspensions of rigid silica rods is investigated, using time-resolved phosphorescence anisotropy, as a function of tracer radius a T , rod volume fraction , and the range Ϫ1 of the double-layer repulsions between the like-charged rods and tracer spheres. A large tracer size a T and a small screening length Ϫ1 appear to maximize hydrodynamic hindrance of tracer diffusion for given . The marked -dependence of the rotational dynamics is primarily determined by the large excluded volumes of the high-aspect ratio rods. Stokes-Einstein-Debye ͑SED͒ scaling of the rotational diffusion coefficients with the inverse viscosity of the rod suspensions holds fairly well, expect for small a T and large Ϫ1 . The ionic strength dependence of deviations from SED scaling is rationalized in terms of an effective hard-rod model with the bare length L replaced by an effective length Lϩ4 Ϫ1 .

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On the Density and Structure Formation in Gels and Clusters of Colloidal Rods and Fibers

Cited by 112 publications

References 25 publications

The role of filament-packing dynamics in powering amoeboid cell motility

The role of filament-packing dynamics in powering amoeboid cell motility

Empirical evaluation of attractive van der Waals potentials for type-purified single-walled carbon nanotubes

Rotational dynamics of colloidal tracer spheres in suspensions of charged rigid rods

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