Mobile superstructures with switchable behavior via redistribution of vibrated particle clusters*

Confining active particles in a free-to-move scaffold is an emerging strategy to create superstructures capable of directed motion and shape change. Many active particle ensembles with a low number density have been proposed, which can deform by internal stress or external stimuli; however, structures with particles close to the jamming condition have been rarely studied. Such densely packed systems are structurally robust and thus advantageous to operate in high-stress environments. Here, we present rigid particle structures consisting of a mobile boundary enclosing a few active polar particles and randomly vibrated nonpolar particles. By tuning the shape and number of polar particles, the superstructures exhibit diverse behaviors ranging from random, rotational to directional motion. We show that particle packing density and mechanical properties of the scaffold additionally modulate dynamic properties – the magnitudes of polarity and chirality – of these structures. Our study paves the way for significant regulation of cluster behavior with small changes in the components of dense systems.