  We have developed several distinct model systems of microtubule-based 3D
active isotropic fluids and have compared their dynamical and structural
properties. The non-equilibrium dynamics of these fluids is powered by three
different types of kinesin motors: a processive motor, a non-processive motor,
and a motor which is permanently linked to a microtubule backbone. The fourth
modification uses specific microtubule crosslinkers to induce bundle formation
instead of a non-specific depletant. In comparison to the formerly developed
systems, each new active fluid formulation has certain enhanced properties.
Firstly, linking motors to the microtubule backbone enhances the fluid lifetime
from hours to several days. Furthermore, switching to the non-processive motors
significantly increases the temporal stability of the active dynamics, while
using specific cross-linkers yields systems that can incorporate other passive
soft materials, such as, polymer gels or liquid crystals. These novel developed
model systems will significantly aid and improve our ability to quantify
diverse phenomena observed in microtubule based active matter.
