Physics of Colloids and Interfaces

The actin cytoskeleton is a complex and dynamic network of proteic filaments. By polymerizing against the cell membrane, it generates a force allowing the cell to move forward. In order to elucidate the physical origin of this phenomenon, we study the reaction of a population of growing actin filaments when a force is applied on it with superparamagnetic beads. We are able to probe the physical mechanism of force generation, along with the influence of the filaments’ geometry on this mechanism.

Superparamagnetic beads are widely used for biochemistry applications in our group and in many others. The physics of these objects is yet complex to grasp. From the observation that the beads are optically anisotropic, we developed an optical setup to characterize how they rotate to orient themselves in an external magnetic field. This movement is a direct consequence of the coupling between beads and field. A model has been established to link the coupling strength to the iron oxide grain polydispersity inside beads.
 

The fragmentation of a compound jet can lead to the creation of liquid core hydrogel capsules having a submillimetric size. We are investigating the destabilization process of this complex jet having an outer liquid layer  characterized by viscoelastic properties. We are also studying the underlying shear layer instability that may occur inside the injector when two miscible liquids are used. Controlling the various interfacial instabilities would allow to generate calibrated liquid core capsules at a high throughput for biotechnology applications.

Funding: ANR CAPCELL

Emulsions have been studied for a long time because of the richness of fundamental related physichochemical phenomena and owing to their wide industrial applications. The development of microfluidics offers new opportunities to investigate emulsion features and behaviors. We are using such a microfluidic route for investigating the  two main mechanisms of destabilization, namely the coalescence of adjacent drops and the molecular transfer between neighboring drops. For example, this approach allowed us to propose the first possible scenario for explaining the well known phase inversion ability of emulsions in presence of shear, a scenario that relies on the coalescent nature of the coalescence. We also probed the stability and the properties of model biological membranes by creating calibrated adhesive droplet pairs separated by a bilayer of phospholipids.