Mechanochemical coupling regulates defect dynamics in active nematics

Active nematics offer a versatile continuum framework for nonequilibrium collective phenomena, such as collective cell migration and tissue morphogenesis. However, the dynamic evolution of active nematics under complex multiphysics fields and the potential mechanism of how the defect dynamics control the distributions of field quantities remain elusive. Here, we establish a mechanochemical model that explicitly couples the orientational order with both morphogen concentration and hydrodynamic flow fields. By solving the active nematohydrodynamic equations, we successfully reproduce the collective motility behavior and topological defects dynamic behavior of the nematic phase that have been widely discovered in experiments, such as quiescent phase, defect generation and annihilation, as well as active turbulence. We find that the morphogen concentration exhibits a robust nonmonotonic relation with the local vorticity magnitude and a linear relation with the flow velocity at relatively low concentration. The viscosity and activity primarily rescale evolution rates and regulate defect density and mean velocity, whereas the gradient alignment strength tunes the balance between defect separation and annihilation, yielding a maximal annihilation efficiency at an intermediate concentration gradient alignment strength. Our results identify the viscosity, activity, and alignment strength as key tunable factors governing the defect-mediated transport and pattern selection in soft active materials, offering new mechanistic insights for reconfigurable microfluidics and tissue-scale morphogenesis.