Soft microcapsules in flow

Microcapsules are promising soft microparticles to control the spatio-temporal delivery of drugs, nutrients or chemicals. These substances are encapsulated in micro-drops, protected from the external fluid by a thin elastic membrane and released by rupture, fusion or cyclic deformations of the membrane. Microcapsules have also the feature to be highly deformable under flow and are so considered as biomimetic models of living cells.

In our group, we work on the relationships between the interfacial rheological properties of their nanometric membrane (e.g. viscoelasticity), their dynamics in flow (e.g. tank treading) and their stability (e.g. wrinkling, folding, break-up).

To gain insigths on the physics of this system, we develop microfluidics methods to tune the size and the elasticity of microcapsules and orginal flow chambers to deform them under controlled stress.

Current collaborators: Marc Léonetti (LRP), Kaili Xie (PhD student), Marc Jaeger (M2P2), Frédéric Dubreuil (CERMAV)

Publications

image Break-up of a microcapsule in an extensional flow.
image Tank-treading of a microcapsule in shear flow. image Wrinkling instability observed with an original flow chamber, PhD Thesis of Kaili Xie.
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Gastrointestinal fluid mechanics

Controlling the spatio-temporal delivery of drugs or nutrients in the gastro-intestinal tract is of prime importance to improve pharmaceutical treatments or to control the nutritional properties of food products. The major constraints to such mixing are the high viscosity and the non-Newtonian characteristics of the gastro-intestinal content and the low velocity of the active mucosa, which together result in low Reynolds numbers. It is most likely that transfers in the lumen should limit biochemical reactions.

With the group of Pr. Roger Lentle in Massey University (NZ), we want to understand and model the mixing strategies developed by the digestive tract at different scales.

To identify the relevant biomechanical and rheological factors that limit mixing and absorption in the small intestinal lumen, we develop methods of high fidelity quantification of intestinal motility, coupled to realistic models of intestinal fluid dynamics as well at the scale of smooth muscle activity (1 mm), as at the one of villi, finger-like structures of around 500 μm length covering intestinal mucosa.

One of our major results has been to show that the intestinal mucosa can be considered as an active microfluidic mixer. Indeed, villous movement during longitudinal contractions is a major radial mixing mechanism that increases dispersion and absorption around the mucosa despite adverse rheological properties of the digesta.

Current collaborators: Roger Lentle (Massey University), Richard Love (Massey Univeristy), Nikhila Vijay (PhD student).

Publications

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Observation of villi (stained in black) movements during mechanical activity of the small intestine.Lattice-Boltzmann simulation of mass transfers generated by this action.

image image Lattice-Boltzmann simulation of mass transfers generated by the mechanical action of small intestine villi.

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Suspensions of soft particles

It is expected that suspensions of artificial deformable microcapsules share common physical features with the blood, especially strong migration and structuration under flow due to their deformability. Typically, soft particles are concentrated in the centre of the channel, leaving a depletion layer near the walls, where rigid particles are more likely to be found. Very recently, such suspensions were numerically studied as models of living fluids such as blood. These studies lead to mechanistic viewpoints of segregation for suspensions of soft microparticles. The salient physical ingredient is deformation induces individual normal forces on particles and migration normal to the flow direction.

In our group, we study experimentally the flow structuration of suspensions of soft microcapsules according to their geometrical and mechanical properties and the segregation in bi-disperse suspensions, i.e. the spatial organisation of the microcapsules.

We have developped a high throughput process of fabrication of suspension of uniform microcapsules in term of size and elastictiy. We can tune the interfacial rheological properties of microcapsules via the physico-chemical properties of the membrane and the process of fabrication in order to understand the processes of segregation in such suspensions.

Current collaborators: Marc Léonetti (LRP), Hugues Bodiguel (LRP), Mehdi Maleki (PhD student), Revaz Chachanidze (Post-Doc)

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Suspension of microcapsules with homogeneous size.