Single-Cell Biophysics: Measurement, Modulation, and Modeling

Single-Cell Biophysics: Measurement, Modulation, and Modeling

Poster Abstracts

94-POS Board 47 Rheological Behavior of Filamentous Networks Governed by the Binding Kinetics of the Cross-Linking Molecules Xi Wei 1 , Vivek B. Shenoy 2 , Yuan Lin 1 . 1 The University of Hong Kong, Hong Kong, Hong Kong, 2 University of Pennsylvania, Philadelphia, PA, USA. Cells employ the actin cytoskeleton, a highly dynamic and complex network of actin filaments inter-connected by various cross-linking proteins, to withstand mechanical load. Although accumulating evidence has shown that the binding kinetics of cross-linkers can significantly influence the rheology of such biopolymer networks, the underlying mechanisms remain poorly understood. Here we present a computational study to address this important issue. Specifically, the rheological behavior of randomly cross-linked actin networks was examined via a combined finite element – Langevin dynamics (FEM-LD) approach where, besides bending and stretching, thermal fluctuations of individual filament have also been taken into account. Each crosslinking molecule was modeled as a combination of linear and rotational springs, resisting both separation and relative rotation between two filaments, whose association/dissociation was assumed to take place in a stochastic yet strain energy – dependent manner. Interestingly, the frequency spectrum of a random network was found to exhibit three distinct regimes. The high-frequency response is dominated by the behavior of independent filaments while the crosslinks can be treated as “static”. At intermediate and low frequencies, unbinding of individual cross-linkers starts to contribute significantly to energy dissipation. In particular, we showed that, under such circumstance, the elasticity of the network mainly depends on the unbroken cross-links while the viscous dissipation is largely determined by the continuous unbinding and rebinding events occurring during the deformation process. Furthermore, we demonstrated that the interplay between the rate of loading and how fast a cross-linker can rupture/reform dictate whether such networks will undergo strain hardening or softening, in good agreement with experimental observations.

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