Bistable Spin Dynamics in Living Chiral Crystals

Starfish embryos of the species Patiria miniata exhibit a characteristic left-handed spin driven by ciliary motion. We investigate the spin dynamics of these embryos as they form a Living Chiral Crystal (LCC). Surprisingly, a transition to a bistable state occurs, where embryos exhibit both left- and right-handed spins. We attribute this bistability to mechanical and hydrodynamic interactions between neighboring embryos, creating a complex interplay between individual spin and collective motion. To capture this phenomenon, we develop a hydrodynamic model to explain the emergent phases of the LCC, including chaotic mixing. These findings can provide insight into a novel mechanism for the emergence of collective behavior in active biological systems, positioning the LCC as a paradigmatic model for exploring nonreciprocal active matter.