Dynamics of Passive and Active Microtubules in Entangled Actin Networks

Rigid rods placed in a viscoelastic network exhibit caged dynamics. They escape their effective cage by passive diffusion along their long axis. We study these escape dynamics by visualizing 3D trajectories of individual microtubules confined in a network of semiflexible actin filaments. The network viscoelasticity is controlled by adjusting the mean actin filament length. Due to their rod-like diffusive properties, longer microtubules are caged on longer timescales than shorter microtubules. To overcome this diffusion-limited escape timescale, we actively drive the microtubules with molecular motors coupled to the background network. Active rods within a network exhibit fundamentally different dynamics. In contrast to the passive case, driven microtubules with longer contour length move through the network more efficiently than shorter microtubules.