Surface roughening and pulsatility of self-assembling microtubule-kinesin active foams

Reconstituted cytoskeletal suspensions serve as quintessential model systems in the study of active materials, due in part to their tunable dynamics and mimicry of hierarchically-assembled structures within living cells. We report on the morphological dynamics and far-from-equilibrium steady-state of one such suspension composed of microtubules and microtubule-tip-adhering kinesin-4 motors. The intrinsic asymmetry of these building blocks leads to an active foam composed of bilayers, reminiscent of passive amphiphilic self-assembly. Under high microtubule concentrations, filaments are recruited via global contraction to the interface of high-density protein encapsulations before roughening into an actively rearranging foam. We describe kinetic roughening of these surfaces in terms of local curvature and dilatational flows to quantify their growth. We also explore the pulsatile nature of this suspension’s foam-like steady state. Together, these descriptions yield insights into a new class of biologically inspired active systems.