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Flow–wave coupling synchronizes oscillations in growing active matter
Oscillatory biochemical signals and mechanical forces must coordinate robustly during development, yet the principles governing their mutual coupling remain poorly understood. In syncytial embryos and cell-free extracts, mitotic waves propagate across millimeter scales while simultaneously generating cytoplasmic flows, suggesting a two-way interaction between chemical oscillators and mechanics. Here, we combine experiments in Xenopu Laevis cytoplasmic extracts with a minimal particle-based model to uncover a mechanochemical feedback that stabilizes wave propagation. Particles grow slowly and shrink rapidly under cell-cycle control ; this asymmetric size cycle, together with size-dependent mechanical interactions, generates flows aligned with the phase gradient. These flows mix particles, promote neighbor exchange, and enhance phase synchronization. As a result, asynchrony generates flows, and these flows eliminate asynchrony, producing a robust transition from a flowing, disordered state to a synchronized, mechanically quiescent one. Our results show that mechanical forces do not merely perturb biochemical wave, but actively maintain their coherence, providing a general mechanism for long-range order in oscillating active matter.