Hydrodynamic interactions significantly alter the dynamics of actin networks and result in a length scale dependent loss modulus.

Actin, the primary component of the cytoskeleton, is the most studied semiflexible filament. Yet, the dynamics of actin filamentous network is still a subject of debate. Here we show that hydrodynamic interactions may significantly alter the time scale of actin network deformation. The alteration may be easily in the range of 2-20 fold depending on the structural conformations and scales of interest. We show that for a single fiber, hydrodynamic interactions between the cytoskeletal mesh-sized segments can change the net force by up to 7 folds. We also demonstrate that cytoskeletal relaxation times are underestimated if hydrodynamic interaction effects are ignored, but bending mode shapes are not appreciably influenced. Ignoring hydrodynamic interactions can result in up to 20-fold overestimation of shear loss modulus in the 2 μm range we investigated. Moreover, in agreement with experimental studies, our models explain a highly length scale dependent loss modulus. Taken together, our data suggest that including hydrodynamic interactions is key to proper modeling and analysis of actin dynamics at any scales and dimensions, and therefore must not be neglected in future models and experimental analyses of cytoskeletal dynamics.