Jean-François Louf, Ph.D.
Department of Chemical Engineering
Auburn University

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ABSTRACT
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.

SPEAKER BIO
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.

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