Single-Cell Biophysics: Measurement, Modulation, and Modeling

Single-Cell Biophysics: Measurement, Modulation, and Modeling

Poster Abstracts

145

94-POS

Board 47

Rheological Behavior of Filamentous Networks Governed by the Binding Kinetics of the

Cross-Linking Molecules

Xi Wei

, Vivek B. Shenoy

, Yuan Lin

The University of Hong Kong, Hong Kong, Hong Kong,

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.