Programmable microrobot reveals odd rheology in sea urchin chiral fluids

Sea urchin embryos break time-reversal and chiral symmetry and display strong shape anisotropy during early development. When densely packed, their geometric frustration and chiral motion generate living chiral fluids that exhibit edge currents and propagating chiral waves. To test for signatures of odd viscosity and control their collective dynamics, we embed nanofabricated magnetic microrobots within these fluids. Programmed microrobot motion excites long-range vortices in the bulk, and the measured misalignment between applied force and resulting velocity quantifies the fluid’s odd viscosity. This work integrates living and synthetic components to actively control the nonequilibrium behavior of living metamaterials.