Poroelastic Couplings in Plants and Hydrogels: From Mechanoperception to Higher Crop Yields
Jean-François Louf, Ph.D.
Department of Chemical Engineering
Plants live quietly, but dangerously. This danger comes from their singular reliance on water. As a result, plants have become experts at manipulating water through varying environmental conditions. Such water flow is fine-tuned by poroelastic membranes, responsive hydrogel coatings, colloidal clogging cycles, and liquid phase changes. Thegoalof our labistouse biomimetic experiments to understand the physical mechanisms at play and improve our fundamental knowledge of plant function,and tocombine this knowledge with soft matter for applications in agriculture and soft robotics. In this presentation, we will investigate (1) how plants can feel without nerves, (2) how they can control water flow without pumps, and (3) how hydrogels can be used as water reservoir for agriculture.(1) Plants are sessile organisms without nerves. As such, they have developed specific methods for carrying information throughout their body in response to mechanical stimuli. However, the specific mechanisms at play are still debated. Motivated by experiments conducted on natural and biomimetic tree branches, we propose a new mechanism responsible for the generation of hydraulic pulses in response to bending as a way for long-distance signaling.Such signals can propagate rapidly throughout the vascular system of the plant, acting like a nervous system but based solely on physical attributes.(2) Despite the lack of actuators, plants are able to manipulate water exquisitely. Inspired by the shapes of membranes separating channels in the plant’s vasculature and in fungi -namely sieve plates, plasmodesmata, and septal nanopores-we investigated the effect of pores inside an elastic membrane to control flow. Our experiments reveal a mechanism where small deformations bend the membrane and constrict the pore, thus reducing flow, while larger deformations stretch the membrane, expand the pore, and enhance flow.Together, our results suggest that intercompartmental flow control in living systems can be encoded entirely in the physical attributes of soft materials. (3) According to the US Drought Monitor, Drought impacted US crops severely in 2021 with near-record lows in soil moisture content. A promising solution for modern agriculture to reduce drought stress in plants is to use hydrogels as water reservoirs. However, confinement in soil can markedly alter the ability of hydrogels to absorb water and swell, hindering their widespread adoption. Unfortunately, the underlying reason remains unknown. By combining measurements on an ideal transparent soil and polymer physics, we show that the extent of hydrogel swelling is determined by the competition between the force exerted by the hydrogel due to osmotic swelling and the confining force transmitted by the surrounding grains. We then confront our results to experiments done with hydrogels in real soil,confirming and providing quantitative principles to predict how hydrogels behave in crops.
Jean-François Louf received his Bachelor degree in Physics at University of Côte d’Azur (France), his master in Mechanical engineering at University of Lyon I (France), and was awarded a Laboratory of excellence PhD fellowship for his doctoral work at Aix-Marseille University(France). He did short postdocs in few different places: one year at Virginia Tech with Sunny Jung, one year with Philippe Marmottant at CNRS in France, one year with Kaare H. Jensen at the Technical University of Denmark, and two years with Sujit S. Datta at Princeton University. He started as an Assistant Professor in Chemical Engineering at Auburn Universityin August 2021. His research operates at the intersection of soft matter physics, fluid dynamics, and organismal plant biology,to tackle both fundamental and applied problems.
Hosts: Drs. David Hu and Saad Bhamla