Wrinkling-dewrinkling transitions in stretched soft spherical shells

Soft shells undergoing intricate buckling and morphological evolutions can serve as a model system for understanding the morphogenesis of organs, tissues, cells, and nuclei. In this paper, we combine experiments, simulations, and theoretical analysis to investigate the wrinkling and subsequent morphological transitions in a soft spherical shell subjected to an outward concentrated force. During loading, the spherical shell first buckles into many shallow radial wrinkles, which soon merge into a single crater-like deep wrinkle, and then the number of wrinkles increases with loading. Surprisingly, after a critical point, all wrinkles disappear and the shell regains an axisymmetric, smooth shape, referred to as dewrinkling. We show how this anomalous wrinkling-dewrinkling transition stems from the interplay between surface curvature and large deformations. Material-independent scaling laws are established from an energy analysis to predict the surface wrinkling pattern, which depends on the loading force. This work provides physical insights into how local forces can regulate the shape evolutions of soft shells, which can take place in, for example, the morphogenesis of developing organisms.