Living tissues are active materials that continuously generate, transmit, and dissipate mechanical stresses across scales. Yet how these stresses give rise to robust three-dimensional shapes remains incompletely understood. In this talk, I will present recent work exploring two complementary physical mechanisms by which cellular monolayers undergo shape transformations: active viscoelastic buckling and nematic-guided morphogenesis.

In the first part, I will delineate the mechanical rules governing epithelial buckling by combining an experimental system that allows us to sculpt epithelial shells and subject them to controlled deflation with a 3D computational model linking cytoskeletal dynamics to tissue mechanics. We show that epithelial buckling emerges from the interplay between the applied loading rate, the viscoelasticity of the actin cortex, and active contractility. We find that epithelial buckling is a multiscale phenomenon involving long-lived supracellular folds as well as short-lived subcellular wrinkles in the actin cortex. By forming epithelial shells with anisotropic curvature, we explore symmetry breaking and direct buckling into predictable wrinkle patterns.

In the second part, I will present a strategy to program tissue shape transformations through the nematic organization of cellular forces. By controlling nematic order and topological defects, we generate tissues programmed with specific stress fields. Using a theoretical framework coupling contractile nematics with thin-sheet mechanics, we show that nematically guided active stresses can drive morphogenesis through Gaussian morphing. Experimentally, detachment of nematic tissues triggers out-of-plane deformations, generating reproducible three-dimensional shapes.

Together, these studies establish a unifying physical framework in which tissue shape emerges from active stresses, viscoelasticity, nematicity, and geometric frustration. Beyond advancing our understanding of morphogenesis, this framework enables the design of synthetic shape-programmable living surfaces.