  We present a scheme for generating shape-dependent, specific bonds between
millimeter scale particles, using acoustic levitation. We levitate particles in
an ultrasonic standing wave, allowing for substrate-free assembly. Secondary
scattering generates shape-dependent attractive forces between particles, while
driving the acoustic trap above its resonance frequency produces active
fluctuations that mimic an effective temperature. We 3D print planar particles,
and show that the local curvature of their binding sites controls the
selectivity for attaching a matching particle. We find that the bound-state
probability and bound-state lifetime can be independently tuned via the binding
site depth and height respectively. Finally, we show that these principles can
be used to design particles that assemble into complex structures.
