  We study the dynamics of pattern formation in a minimal model for active
mixtures made of microtubules and molecular motors. We monitor the evolution of
the (conserved) microtubule density and of the (non-conserved) nematic order
parameter, focusing on the effects of an "anchoring" term that provides a
direct coupling between the preferred microtubule direction and their density
gradient. The key control parameter is the ratio between activity and
elasticity. When elasticity dominates, the interplay between activity and
anchoring leads to formation of banded structures that can undergo additional
bending or rotational instabilities. When activity dominates, the nature of
anchoring instead gives rise to a range of active cellular solids, including
aster-like networks, disordered foams and spindle-like patterns. We speculate
that the introduced "active model C" with anchoring is a minimal model to
describe pattern formation in a biomimetic analogue of the microtubule
cytoskeleton.
