Active gas-to-solid phase transitions ruled by responsive active pumping

The rich collective dynamics of living organisms emerge from the interplay between individual activity and local interactions. While the self-assembly of different active phases from local interaction rules and symmetries is well understood, how and when active agents pump their internal energy and the consequences of their strategies on self-assembly are still underexplored.

Here, we demonstrate the crucial role of responsive active pumping in collective dynamics by introducing a synthetic active material assembled from non-motile isotropic active particles, realized as self-sustained oscillators activated through contact-charge electrophoresis. By controlling the active pumping mechanism from internal to spatial degrees of freedom, we demonstrate the guiding of self-assembly and the triggering of a transition from an active gas to an active crystal.

Our work highlights the importance of responsive active pumping in dictating the collective behaviors of active agents. These findings underscore the need to unify active pumping strategies with activity-induced interactions in designing self-assembled smart active materials or accounting for complex biological emergent behaviors.