Gait induced self-organization in shape changing active matter

In a recent study [Vardhan et al. (arxiv: 2206.04782)], we reported the discovery of “gliders”, which are dynamically bound, locomoting excitations that emerge spontaneously from stochastic rigid-body collisions in a shape-changing, programmable active matter system known as “smarticles”. In dense ensembles, these gliders self-assemble into chain-like structures by spontaneously linking with other robots in their vicinity. This results in a long-range spatial order with a characteristic lifetime of 8-10 periods. We study how initially compressed collectives expand to lower density configurations using simulations and experiments and analyze the degree of self-organization for various gaits (i.e., closed loops in the shape space). We measure instantaneous contact and construct a graph where the vertices are the spatial coordinates of each particle and the edges represent the pairwise contacts, hence obtaining the average number of neighbors per gait period for each smarticle. We observe that time-irreversible gaits responsible for producing gliders also give rise to chains with closed loops having 4 neighbors on average. Further, we observe a time-reversible gait produces long, aligned chains with most agents having 2 neighbors on average. The emergent order is thus found to be controlled by gait dynamics.