Dehydration-induced corrugated folding in shape-morphing leaves

Plant leaf morphogenesis, giving rise to vast varieties of flower and leaf shapes, has been of interest to researchers in both biology and engineering. Leaves also demonstrate intriguing shape-morphing behaviors upon changes in the environment. For example, the leaves of Rhapis excelsa fold into a corrugated structure with the loss of water. To understand this interesting phenomenon, we explore the mechanical basis and the cellular mechanism of the corrugated leaf folding. We experimentally examine the cellular structures in the leaf that induce folding - the ‘hinge’ cells that undergo higher volume shrinkage than the others, which introduce the strain-mismatch within the leaf - and investigate the mechanism by numerical simulations. Additionally, we develop a mathematical model for describing the dynamics of the water loss, as well as predicting the folding angle. These findings provide insights of how plant leaves in nature change their shapes by mechanical principles in response to environment change, which may have biological functions for plant survival. To further explore its potential applications, the mechanism of leaf folding we observed is implemented into the design of biomimetic soft machines that made of hydrogels and show self-folding ability with water loss.