Reentrant Rigidity Transition in Planar Epithelia with Volume- and Area Elasticity

We recover a rigidity transition in 3D epithelial monolayers, described by cell Volume- and Area Elasticity (VAE). An in-plane isotropic strain drives a reentrant columnar-to-sqamous rigidity transition, with a critical point near the unit cell aspect ratio. In addition to the vanishing shear modulus, the phase diagram also features floppy states with zero in-plane bulk modulus and a discontinuous columnar-squamous transition, controlled by the lateral tension. Our results provide a 3D context to the rigidity transition of the well-studied 2D Area- and Perimeter-Elasticity (APE) model of epithelia, offering a resolution to a counterintuitive compression-induced tissue softening predicted by the 2D model.