I like interfaces, especially soft ones. Looking at their shape and motion, understanding how they developped ... and crossing them.
The same is true about geographics frontiers and scientific disciplines. I was trained as a physicist, but I had the chance to collaborate with people from many countries, with backgrounds in mechanics, biology, mathematics ... I thank all of them for introducing me to many mysterious other sides.
Blood platelet formation in biomimetic channels (video here)
with Mathilde Reyssat (ESPCI), Antoine Blin, Aurélie Magniez and Dominique Baruch (PlatOD)
Post-doc : Ilyesse Bihi
Platelets are small enucleated blood cells, that are responsible for the healing of wounds. Because of a genetic disease of after a treatment against cancer, many patients require platelet transfusion. Producting platelets concentrate meeting these requirement is challenging due to the increasing needs and to the short lifetime of platelet, that makes their conservation uneasy. We produce microchannels that mimic the blood vessels in which blood platelets are created in vivo, with the objective of producing platelets concentrates in vitro.
Cells like platelets or white blood cells circulate in the blood flow, but they are also able to interact with the vessel walls and keep moving forward by rolling. I am also interested in the competition between these two mechanisms. How are cells caught by the wall at the right time and place ? What does it take to stop them ?
Dynamics of flowing capsules
with Badr Kaoui, Anne-Virginie Salsac and Dominique Barthès-Biesel (BMBI, UTC)
PhD student : Doriane Vesperini
We study the shape, dynamics and trajectory of capsules in diverse microfluidic devices in order to characterize their mechanical properties or sort them according to their size or rigidity. We work with artificial capsules or different sizes as well as with living cells.
Myco-fluidics for bioremediation
with Antoine Fayeulle and Isabelle Pezron (TIMR, UTC)
PhD student : Claire Baranger
We use microfluidic chambers as transparent models of soil to study fungal growth and understand how fungi degrade persistent organic pollutants.
Surface waves in a liquid foam
with Pablo Cobelli and Guillaume Lagubeau at Philippe Petitjeans' team in ESPCI
We use a fringe projection technique to image the deformation of the free surface of a liquid foam around a site of impact. Foam is a complex fluid, and therefore behaves either like a solid or like a liquid. We evidenced the propagation of solid-like Rayleigh waves after impact, some of them travelling at unusually high speed. These supershear soft Rayleigh waves are a laboratory-scale analogue of the supershear cracks that are sometimes observed by geophysicists.
Life and death of bacteriophages in liquid environment
INSERM U 1001, Paris, France
A bacteriophage, or phage, is a virus that infects bacteria. Like all viruses, it depends on its host's cell machinery to perform all the tasks required for its propagation, like protein synthesis and assembly. Outside the host, in spite of its total lack of activity, the phage changes and loses its infectious properties. Phage inactivation, like radioactive decay, is an exponential process, and the mortality rate of phages depends on temperature. The goal of this study is to investigate the variation of this mortality rate with the solvent used to store the phages. We worked with phages that infect E. coli, a bacteria present in mammals' guts. In their life cycle, they spend time both in the digestive system of animals - a warm and crowded environment - and outside, for example in soil or in rivers. What is the best strategy for them ? Optimizing their infection efficiency in the well-controlled conditions encountered in the gut ? Or keeping the ability to survive in the highly variable, sometimes hostile, wild world ?
Surfactant liquid-crystalline organization in microfluidic device
Department of Complex Fluids, Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany
Surfactants are molecules which are partly hydrophilic and partly hydrophobic. When put in solution in water, they self-arrange into structures that allow them to hide their hydrophobic regions. One way to achieve this is forming bilayers. When these sandwich-like structures, formed by non-ionic surfactant at low water concentration, are soaked in water, they start swelling and growing fingers.
Impacts on a liquid bath
PMMH, ESPCI, Paris - in collaboration with Guillaume Dupeux
Advisors : David Quéré, Christophe Clanet
Having a high speed camera allows one to observe the many things that happen when a solid sphere hits the surface of a liquid bath at large velocity. The sphere decelerates, and by measuring this deceleration we can deduce the friction force exerted on the sphere by the fluid. We have discovered that a liquid foam, a shaving cream that usually has weird flowing properties, behaves like a simple viscous fluid when it is highly sheared. Such violent impacts also cause air entrapment. We describe the shape of the cavity created in the liquid : tunnel-like in foam, vase-shaped in a viscous oil, it can look like a spiral in water if the projectile is spinning.
Capillary capture
PMMH, ESPCI, Paris - in collaboration with Guillaume Dupeux and Laust Tophøj (Denmark Technical University)
Advisors : David Quéré, Christophe Clanet
Wet surfaces are sticky. When falling on a wet floor, a solid particle can bounce it it has enough kinetic energy. Otherwise, it stays glued in the liquid film. Existing theories rely on lubrication approximation and predict a capture threshold depending mostly on the viscosity of the fluid. We show that by tuning the wettability of a falling sphere, we can significantly modify this threshold.
Self-healing and capture in bamboo foam
PMMH, ESPCI, Paris - in collaboration with Laurent Courbin and Howard Stone at Harvard University
Advisors : David Quéré, Christophe Clanet
Soap films are famous for being fragile objects. And still, it happens that an object crosses a film without breaking it ! We studied this surprising self-healing mechanism and realised that a part of the incoming body's energy was dissipated in the process. It is even possible, with many soap films, to stop it completely. This happens in a tube filled with a bamboo foam (large bubbles separated by parallel films). This constitues another example of capillary capture, and it is limited to the case of small and light spheres, whose weight can be compensated for by capillary forces.
Bubble-powered micromixing
Northwestern University, Evanston, USA
Advisor : Sascha Hilgenfeldt
Mixing fluids at small scale is a classical challenge in microfluidics. The purpose of this project was to investigate the mixing efficiency of ultrasound-driven oscillating microbubbles. Such bubbles have been shown to create shear in the neighbouring fluid, so much so that they can break open cells and vesicles. At microscopic scale, stirring is not enough to achieve successfull mixing: the motion has to be non-reversible. Asymmetry can be introduced in microbubble chips by patterning channel walls, adding bumps next to the bubbles. This allows passive particles to be transported by the flow. A numerical analysis allowed to map the flow in such chips, providing evidence of efficient mixing in some regions of the channel.