  When objects are packed in a cluster, physical interactions are unavoidable.
Such interactions emerge because of the objects geometric features; some of
these features promote entanglement, while others create repulsion. When
entanglement occurs, the cluster exhibits a global, complex behaviour, which
arises from the stochastic interactions between objects. We hereby refer to
such a cluster as an entangled granular metamaterial. We investigate the
geometrical features of the objects which make up the cluster, henceforth
referred to as grains, that maximise entanglement. We hypothesise that a
cluster composed from grains with high propensity to tangle, will also show
propensity to interact with a second cluster of tangled objects. To demonstrate
this, we use the entangled granular metamaterials to perform complex robotic
picking tasks, where conventional grippers struggle. We employ an electromagnet
to attract the metamaterial (ferromagnetic) and drop it onto a second cluster
of objects (targets, non-ferromagnetic). When the electromagnet is
re-activated, the entanglement ensures that both the metamaterial and the
targets are picked, with varying degrees of physical engagement that strongly
depend on geometric features. Interestingly, although the metamaterials
structural arrangement is random, it creates repeatable and consistent
interactions with a second tangled media, enabling robust picking of the
latter.
