  We study the dynamics of quasi-two-dimensional concentrated suspensions of
colloidal particles in active gels by computer simulations. Remarkably, we find
that activity induces a dynamic clustering of colloids even in the absence of
any preferential anchoring of the active nematic director at the particle
surface. When such an anchoring is present, active stresses instead compete
with elastic forces and re-disperse the aggregates observed in passive
colloid-liquid crystal composites. Our quasi-two-dimensional "inverse"
dispersions of passive particles in active fluids (as opposed to the more
common "direct" suspensions of active particles in passive fluids) provide a
promising route towards the self-assembly of new soft materials.
