Fluid pumping and active flexoelectricity can promote lumen nucleation in cell assemblies

Significance
The presence of fluid-filled cavities is a common feature of multicellular structures. Nucleation and growth of such lumens typically involve the pumping of fluid by cells, which relies on active ion transport. In this paper, we use a continuum description of a spherical cell assembly that takes into account fluid pumping, electric currents, and electric fields to explore the physical mechanisms of lumen formation. We highlight the role of the coupling between tissue bending and electric fields, called tissue flexoelectricity, in the lumen-nucleation process. We show, in particular, that understanding lumen formation requires one to consider the combined effects of mechanical, electrical, and hydraulic mechanisms.