  Cluster formation of microscopic swimmers is key to the formation of biofilms
and colonies, efficient motion and nutrient uptake, but, in the absence of
other interactions, requires high swimmer concentrations to occur. Here we
experimentally and numerically show that cluster formation can be dramatically
enhanced by an anisotropic swimmer shape. We analyze a class of model
microswimmers with a shape that can be continuously tuned from spherical to
bent and straight rods. In all cases, clustering can be described by
Michaelis-Menten kinetics governed by a single scaling parameter that depends
on particle density and shape only. We rationalize these shape-dependent
dynamics from the interplay between interlocking probability and cluster
stability. The bent rod shape promotes assembly even at vanishingly low
particle densities and we identify the most efficient shape to be a semicircle.
Our work provides key insights into how shape can be used to rationally design
out-of-equilibrium self-organization, key to creating active functional
materials and designing targeted two-component drug delivery.
