  Fluid-structure interactions between active and passive components are
important for many biological systems to function. A particular example is
chromatin in the cell nucleus, where ATP-powered processes drive coherent
motions of the chromatin fiber over micron lengths. Motivated by this system,
we develop a multiscale model of a long flexible polymer immersed in a
suspension of active force dipoles as an analog to a chromatin fiber in an
active fluid -- the nucleoplasm. Linear analysis identifies an orientational
instability driven by hydrodynamic and alignment interactions between the fiber
and the suspension, and numerical simulations show activity can drive coherent
motions and structured conformations. These results demonstrate how active and
passive components, connected through fluid-structure interactions, can
generate coherent structures and self-organize on large scales.
