Active polymer hydrodynamics

Recent spectroscopy experiments on interphase chromatin have uncovered the existence of long-ranged coherent motions on the scale of microns and persisting for seconds. These motions were found to be ATP-dependent suggesting the involvement of molecular motors. Motivated by these observations, we use Brownian dynamics simulations to elucidate the effects of microscale activity on the behavior of long flexible polymer chains in viscous solvents. We develop a coarse-grained model where active events are modeled as stochastic force dipoles, which affect chain dynamics and also drive long-ranged fluid flows. Numerical simulations in unconfined environments demonstrate the key role played by hydrodynamic interactions, where extensile dipolar activity is shown to result in chain stretching and nematic alignment whereas contractile activity effectively enhances fluctuations. The stretching of the polymer in extensile systems is accompanied by an increase in its persistence length or effective bending rigidity. We characterize the transition to stretching as a function of dimensionless dipole strength and probability of motor attachment.