Bio-mimetic soft filters: when thickness tunes the flow

In plants, energy-rich sap flows through tiny living vessels called phloem. Each element of this hydraulic network is separated from its neighbor by a perforated filter-like element called a sieve-plate (SP). SP filters are believed to play a role in wound-response by blocking the flow when the tissue is damaged. However, it is unknown how the filter is occluded. Recently, we have been able to observe a pronounced bending of SP following injury. The origin and effects of this deformation is not well understood, but we suggest it could help blocking the flow almost immediately. To address this issue, we investigate the poroelastic response to sudden bending of both natural and artificial SP made of a polymer membrane with a small central hole. In the artificial systems we observe that depending on the membrane thickness/hole diameter ratio, the bending of SP either increases or reduces the hole diameter, subsequently increasing or reducing the flow. We propose a simple energetic model to explain the observed flow variations and discuss our results in the context of plant hydraulics.