Morpho-mechanics of pressurized cellular sheets: From moss leaves to soft robotics.

Everyday experience shows that cellular sheets are stiffened by the presence of a pressurized gas: from bicycle inner tubes to bubble wrap, the presence of an internal pressure increases the stiffness of otherwise floppy structures. The same is true for plants, with turgor pressure (due to the presence of water) taking the place of gas. However, simple attempts to rationalize this mechanical stiffening suggest that the stiffness should be independent of the pressure, at odds with everyday experience. We will present a model of single-cell-thick sheets and show how a pressure-dependent bending stiffness may arise. We will demonstrate how our model rationalizes observations of turgor-driven mechanisms in plant cells and suggests that turgor is unlikely to provide significant structural support in many monolayer leaves. However, we will show that turgor does provide a way to control the shape of the sheet, in accordance with observations of curling upon drying of moss leaves. Finally, we will present a pneumatically inflated device inspired by our model, whose cell-level asymmetry creates a curvature which mimics that of moss leaves: curved at low pressures, while flat at high pressures.