# Air invasion in a biomimetic leaf-on-chip

François-Xavier Gauci, Celine Cohen, Ludovic Jami, Ludovic Keiser, Xavier Noblin, Virgile Thiévenaz, Eric Badel, Hervé Cochard, Jose Manuel Torres

Ruiz, Benjamin Dollet, et al.

► To cite this version:

François-Xavier Gauci, Celine Cohen, Ludovic Jami, Ludovic Keiser, Xavier Noblin, et al. Air invasion in a biomimetic leaf-on-chip. GDR PhyP - Biophysique et biomécanique des plantes, Mar 2024, Caryl-le-Rouet, France. hal-04882858

HAL Id: hal-04882858

https://hal.science/hal-04882858v1

Submitted on 13 Jan 2025

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# Air invasion in a biomimetic leaf-on-chip

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GDR PhyP

11th-13th March 2024

Carry-le-Rouet

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François-Xavier Gauci

Céline Cohen, Ludovic Jami, Ludovic Keiser
and Xavier Noblin

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UNIVERSITÉ
CÔTE D'AZUR

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# How does the sap climb from roots to leaves?

* The roots absorb water in soil

* Water is pulled to leaves by **evapotranspiration**

* An ascending **water column** is generated in the **xylem**

* Negative pressure (gravity, viscosity, soil effect)

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# Plant embolism, a global threat

> « soil moisture deficits are the main driver of xylem embolism, the primary cause of plant mortality »
> (Intergovernmental Panel on Climate Change, 2021)

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H. Cochard, INRAE

A bubble generated by cavitation or
air-seeding

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Brodribb et al., PNAS, 2016

Progression of embolism in a
natural leaf

* Intermittent dynamics

* Hierarchical
# Taking benefit from PDMS

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Side view

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Dollet et al., JRSI, 2019

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Top view

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Air

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Water

Entrance channel

Stop and Go
↑
Constriction

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Intermittent dynamics
Elasto-capillary coupling

Exit channel

Keiser et al., JFM, 2022

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Cross-section (confocal imaging)

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From a 1D

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to a 2D network

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Overcoming real leaves
complexity

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Biomimetism

**Microchannels** in PDMS to mimic
a leaf evapotranspiration

**Coupling**
between all the
channels
Leaf-like venation network

* Closer to a real leaf venation network

* Multi-order network (1, 2, 3...) of decreasing width

* 10 µm-width **constrictions** between channels

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# Embolism in artificial leaves

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PDMS membrane
made in clean room

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Water

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Air

Biomimetic leaf
(uman side view)

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Air invades the
system as water
evaporates through
the PDMS membrane

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Biomimetic chip vs real leaf

<figure><img src="image_33.png" /><figcaption>My experiment</figcaption></figure>

<figure><img src="image_34.png" /><figcaption>Brodribb et al., PNAS, 2016</figcaption></figure>

Presence of constrictions → **Intermittency**

**Hypothesis**: A single type of constriction equally distributed induces **no hierarchy**

→ **Reinforce biases** to recover hierarchical dynamics
Controlling embolism pathway via constrictions width

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Affine distribution of
constriction widths
from 10 to 50 µm

$$ \Delta P_{Laplace} = P_{air} - P_{water} = \frac{2\gamma}{R} $$

with $R_{max}$ about the constriction width
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Simulation

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Experiment

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Order 1

Order 2

Order 3

Order 4

0

Time
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For a given constriction width, the **probability** to embolize the order 1 increases
# Controlling embolism pathway via connectivity

## Simulation

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Increasing connectivity between order 1-channels increases the directivity of embolism

## Experiment

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In summary

Constriction **width** distribution

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**Number** of constrictions between different types of channels

Numerical
simulations

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* Valuable device because of the limits of observational methods on real leaves

* **Microfluidic platform** to perform experiments and investigate different leaf structural parameters

* Biomimetic device **qualitatively similar** to real leaves

* The key role of **xylem constrictions**
<figure><img src="image_54.png" /><figcaption>High-speed imaging of a
mulberry tree leaf</figcaption></figure>

V. Thievenaz, PIAF, Clermont-Ferrand

Relate embolism
dynamics in artificial
and real leaves

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V. Thievenaz

Towards biomimetic tissue

► PDMS too **compliant** and **hydrophobic** : no negative pressure

► Too **dry**: no bound water

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Develop **hydrogel** devices (Ludovic Jami)

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<figure><img src="image_58.png" /><figcaption>Benjamin Dollet
Philippe Marmottant</figcaption></figure>

<figure><img src="image_59.png" /><figcaption>Céline Cohen
François-Xavier Gauci
Ludovic Jami
Ludovic Keiser
Xavier Noblin</figcaption></figure>

<figure><img src="image_60.png" /><figcaption>Eric Badel
Hervé Cochard
Virgile Thiévenaz
José Torres-Ruiz</figcaption></figure>
# Conclusions

* Valuable device because of the limits of observational methods on real leaves

* A **microfluidic platform** to perform experiments and investigate different leaf structural parameters

* Biomimetic device **qualitatively similar** to real leaves

* The key role of **xylem constrictions**

## Towards biomimetic tissue

* PDMS too **compliant** and **hydrophobic** : no negative pressure

* Too **dry** : no bound water

<figure><img src="image_61.png" /></figure>

Develop **hydrogel** devices (L. Jami)

5 mm

<figure><img src="image_62.png" /></figure>