Mechanical response of active gels

Abstract

Abstract. -We study a model of an active gel of cross-linked semiflexible filaments with additional active linkers such as myosin II clusters. We show that the coupling of the elasticity of the semiflexible filaments to the mechanical properties of the motors leads to contractile behavior of the gel, in qualitative agreement with experimental observations. The motors, however, soften the zero frequency elastic constant of the gel. When the collective motor dynamics is incorporated in the model, a stiffening of the network at high frequencies is obtained. The frequency controlling the crossover between low and high frequency network elasticity is estimated in terms of microscopic properties of motors and filaments, and can be as low as 10 −3 Hz.

Molecular motors stiffen non-affine semiflexible polymer networks

“…So far, this correspondence has been understood in the context of stretchingdominated networks, with nonlinear filaments [18][19][20]. The present work shows that this analogy is more general.…”

“…This nonlinear response can be exploited using molecular motors [4,7]; the network stiffness can be varied by orders of magnitude, depending on motor activity. A quantitative understanding of such active biological matter poses a challenge for theoretical modeling [3,[16][17][18][19][20][21].The nonlinear mechanical response of reconstituted biopolymer networks in many cases reflects the nonlinear force-extension behavior of the constituting cross-links or filaments [9-11, 14, 22]. For such networks, there is both theoretical and experimental evidence that internal stress generation by molecular motors can result in network stiffening in direct analogy to an externally applied uniform stress [4,7,[18][19][20]23].…”

“…A quantitative understanding of such active biological matter poses a challenge for theoretical modeling [3,[16][17][18][19][20][21].…”

Inherently unstable networks collapse to a critical point

“…Taken together, these cellular proteins form an elastic network with contractility induced by nonequilibrium motor stresses [16,18]. The motors generate forces that propagate through the network, changing the viscoelastic properties, structure, and fluctuations in living systems [16,17,[19][20][21][22][23][24][25][26][27][28][29][30].…”

Hydrodynamic Theories for Flows of Active Liquid Crystals and the Generalized Onsager Principle

“…More generally, active liquid crystals are described by kinetic theories, generalizing the Doi-Edwards-Hess formalism for passive liquid crystals, cf. studies by Marchetti and Liverpool, Shelley, Saintillan et al and Forest et al [1,[24][25][26][27][28][29][30]. In this formulation, microscopic symmetry is tacitly incorporated through the interaction potential, self-propelling velocity, as well as phenomenologically modeled active forces [31].…”