Swelling of a Non-Vascular-Plant-Inspired Soft Composite

Abstract

Even without the aid of muscle, plant tissue drives large, forceful motion via osmosis-driven fluid flow. Hydrogels are well-known synthetic materials that mimic this osmotic mechanism to achieve large swelling deformations. Yet hydrogels can be limited by a loss of stiffness as their swelling increases. Here we demonstrate that a synthetic, plant tissue analog (PTA) can mimic the closed-cell structure and osmotic actuation of non-vascular plant tissue, enabling the emergence of turgor-pressure-induced stiffness and leading to more forceful swelling deformations. PTAs consist of micron-sized saltwater droplets embedded within thin, highly stretchable, selectively-permeable polydimethylsiloxane PDMS walls. When immersed in water, PTAs reach a state of equilibrium governed by the initial osmolyte concentration (higher produces more swelling) and cell wall mechanical response (stiffer and less stretchable yields less swelling). Given these behaviors, PTAs represent an alternate class of aqueous, autonomous synthetic materials that, like hydrogels, may benefit biomedical applications.