Phase diagram of microtubule and end-directed motor proteins

Extensive efforts over the past few years have focused on understanding the non-equilibrium
macroscale behaviors of filamentous biopolymers such as microtubules and actin filaments that
are driven by associated molecular motors. Previously studied systems exhibited either robust
contractions or extensile stresses that powered turbulent flows. Despite these effort our
understanding of how various microscopic parameters determine the symmetries of the emergent
active stresses remains incomplete. To connect microscopic dynamics to macroscale behaviors
we measured the phase diagram of a new system of microtubule filaments and end-accumulating
kinesin molecular motors. Our results demonstrate mechanisms that can be used to switch
between extensile and contractile stresses, as well as a range of new dynamical pathways and
structures that are reminiscent of those observed in equilibrium amphiphilic systems.