Fluctuating Elasticity Mode in Transient Molecular Networks

Nava, Giovanni; Rossi, M.L.; Biffi, Sofia; Sciortino, Francesco; Bellini, Tommaso

doi:10.1103/physrevlett.119.078002

Cited by 29 publications

(46 citation statements)

References 25 publications

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“…They have also been observed in passive colloidal gels, where they have been attributed to rearrangement events triggered by internal stress resulting from the rapid, disordered gelation process [71]. They have furthermore been found in DNA tetravalent networks, where they have been attributed to fluctuations in local elasticity and connectivity [87].…”

Section: Discussionmentioning

confidence: 95%

Uncovering the dynamic precursors to motor-driven contraction of active gels

2019

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Cells and tissues have the remarkable ability to actively generate the forces required to change their shape. This active mechanical behavior is largely mediated by the actin cytoskeleton, a crosslinked network of actin filaments that is contracted by myosin motors. Experiments and active gel theories have established that the length scale over which gel contraction occurs is governed by a balance between molecular motor activity and crosslink density. By contrast, the dynamics that govern the contractile activity of the cytoskeleton remain poorly understood. Here we investigate the microscopic dynamics of reconstituted actin-myosin networks using simultaneous real-space video microscopy and Fourier-space dynamic light scattering. Light scattering reveals rich and unanticipated microscopic dynamics that evolve with sample age. We uncover two dynamical precursors that precede macroscopic gel contraction. One is characterized by a progressive acceleration of stressinduced rearrangements, while the other consists of sudden rearrangements that depend on network adhesion to the boundaries and are highly heterogeneous. Our findings reveal an intriguing analogy between self-driven rupture and collapse of active gels to the delayed rupture of passive gels under external loads.

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Section: Discussionmentioning

confidence: 95%

Uncovering the dynamic precursors to motor-driven contraction of active gels

2019

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“…Despite these differences, the effect of such local decorrelations on the small q dynamics is system independent. The local changes of elasticity brought in by these local events possibly propagate via the vibrational modes of the system [31] resulting in the decay of the collective density (N/V ) fluctuations at large distances controlled by changes not in the number of particles N but in the volume V .…”

Section: Discussionmentioning

confidence: 99%

“…More recently, a q 0 mode has been reported for equilibrium gels of DNA tetrafunctional nanostars [30,31] in which a short self-complementary DNA sequence provides a temperature-controllable link between different particles. This q 0 relaxation dynamics has been interpreted as originating from local elasticity fluctuations propagating through the system [22,31]. A recent simulation study of a particle model for vitrimers, binary-mixture networks in which the microscopic dynamics is slaved to a bond-swapping process [32], has also reported a clear q 0 dependence for the collective dynamics extending over more than one order of magnitude in q.In this Letter we explore the possibility that a q 0 dependence of the collective relaxation time is much more common than previously thought, being a generic feature of systems with slow dynamics, including systems composed of atoms and molecules.…”

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confidence: 99%

q-Independent Slow Dynamics in Atomic and Molecular Systems

2019

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Investigating million-atom systems for very long simulation times, we demonstrate that the collective density-density correlation time (τα) in simulated supercooled water and silica becomes wavevector independent (q 0 ) when the probing wavelength is several times larger than the interparticle distance. The q-independence of the collective density-density correlation functions, a feature clearly observed in light-scattering studies of some soft-matter systems, is thus a genuine feature of many (but not all) slow-dynamics systems, either atomic, molecular or colloidal. Indeed, we show that when the dynamics of the density fluctuations is due to particle-type diffusion, as in the case of the Lennard Jones binary mixture model, the q 0 regime does not set in and the relaxation time continues to scale as τα ∼ q −2 even at small q.The wave-vector (q) dependence of the dynamics of atomic, molecular, and colloidal systems close to dynamic arrest has been the focus of intense research [1][2][3][4][5][6][7][8][9][10][11]. In particular, the q-region that corresponds to the nearest neighbour distance in glass-and gel-forming systems has revealed a series of interesting phenomena [12,13]: (1) a two-step relaxation for both self and collective density correlation functions, indicating a faster intra-cage motion and a slower structural relaxation (α-relaxation), respectively; (2) a significant stretching of the α-relaxation, which originates from the coupling between distinct modes [14,15]; (3) a deviation from the diffusive q −2 behavior of the self correlation time; (4) oscillations in the q-dependence of the collective relaxation time, often in phase with the oscillation of the structure factor; (5) a faster decay of the self dynamics compared to the collective one, indicating that relative particle displacements play an important role in the decorrelation of the system.The region at very small q, where the wavelength is much larger than the inter-particle distance, has also been thoroughly characterized. Here, conservation laws in one-component systems determine a three-mode decay of the collective correlation functions [16]: two modes associated with damped sound waves (the Brillouin peaks) and one to the damped decay of the heat diffusion (the Rayleigh peak). In all three cases, the damping time follows a q −2 dependence. In the case of glasses (where the α-relaxation time is longer than the experimental observation), a clear cross-over has been identified between the region where the system can be considered an elastic continuum and the region where an excess of vibrational states [17,18] is superimposed to the Debye density of states [19][20][21].In some colloidal systems, where the size of the particles provides access to smaller ratios between the wavelength of the probe radiation and the interparticle distance, a q-independent (q 0 ) relaxation mode has been reported. From the early measurements in polymer melts in which entanglement induces an effective transient network [22][23][24], evidence of a q 0 mode has be...

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“…However, viscoelastic materials can resist mechanical stress only for a limited time, after which the system suddenly loses its mechanical percolation, a process which is known as fracturing [8][9][10][11]. Crack initiation of viscoelastic materials occurs stochastically [1,11] due to fluctuations in the local density of bound linkers [12,13], which eventually results in fracture due to rapid crack propagation [14]. In order to understand the fracturing behavior of transient networks, one needs to understand the linker dynamics.…”

Section: Introductionmentioning

confidence: 99%

Crosslinker mobility weakens transient polymer networks

Mulla

Koenderink

2018

Phys. Rev. E

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Transient networks comprised of polymers connected by short-lived bonds are a common design theme for both biological and synthetic materials. Transient bonds can provide mechanical rigidity, while still allowing for visco-elastic flows on timescales longer than the bond lifetime. In many biological polymer networks such as the actin cytoskeleton, the short-lived bonds are formed by accessory proteins that diffuse away after unbinding. By contrast, bonds in synthetic networks, such as the pendant groups of telechelic polymers, can only rebind in the same location. Using a recently developed theoretical model of the fracturing of visco-elastic materials, we here investigate the effect of linker mobility on the bond dynamics of a network under stress. We find that although mean field properties such as the average bond linker lifetime are barely affected by bond mobility, networks cross linked by mobile bonds fracture more readily due to 'leaking' of linkers from crack areas to less stressed regions within the network. We propose a theoretical model to describe the redistribution of mobile linkers, which we validate by simulations. Our work offers insight into a potential trade-off that cells face, between fracture strength versus the modularity and tight dynamic control offered by mobile linkers. arXiv:1805.12431v1 [cond-mat.soft]

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Fluctuating Elasticity Mode in Transient Molecular Networks

Cited by 29 publications

References 25 publications

Uncovering the dynamic precursors to motor-driven contraction of active gels

Uncovering the dynamic precursors to motor-driven contraction of active gels

q-Independent Slow Dynamics in Atomic and Molecular Systems

Crosslinker mobility weakens transient polymer networks

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