Job offers

2023 – Master 2 Internship and/or PhD thesis « transport of phospholipidic vesicles in temperature and concentration gradients »

In collaboration with D. Cuvelier at Institut Curie

The cryoperservation of living cells ie the preservation of living cells by freezing them is crucial for medecine and biology from blood storage to clinical studies. During freezing, cells are often damaged either because they are squeezed between growing ice crystals or because they undergo strong osmotic pressure gradients due to rejection of solutes by the ice which lead to volume variations of the cells leading to their rupture.

Our project aims at understanding the mechanisms at play during the freezing of cells. To this end, our global strategy is to mimic the freezing process by studying the behaviour of model soft and permeable particles of increasing complexity during freezing.

In the past, we have already studied the behaviour of simple emulsion droplets during freezing and showed that the shape and velocity of the drops is controlled by the solute concentration in the solution. Indeed the solute is rejected by the ice crystals and segregates at the ice/solution interfacecreating a strong concentration gradient inducing a phoretic motion of the drops [1-4].

Our goal is now to study permeable particles such as phospholipidic vesicles which mimick cells. In this case, the internal core of the vesicles may freeze and exchange of solute may occur between the core and the solution leading to volume variations.

[1] Dedovets, D., Monteux, C., & Deville, S. Five-dimensional imaging of freezing emulsions with solute effects. Science, 2018

[2] Dedovets, D., Monteux, C., & Deville, S. A temperature-controlled stage for laser scanning confocal microscopy and case studies in materials science. Ultramicroscopy, 195, 1-11, 2018

[3] S Tyagi, C Monteux, S Deville, Objects interacting with solidifying fronts : thermal and solute effecs, Materialia, 2019

[4] S Tyagi, C Monteux, S Deville, Solute effects on dynamics and deformation of emulsion droplets during freezing, Soft Matter, 2022

Reference on dead end pore geometry to produce controlled concentration gradients

[5] Shin, S. Stone, H.A et al., Size-dependent control of colloid transport via solute gradients in dead-end channels. Proc. Natl. Acad. Sci. U.S.A. 113, 257–261 (2016)

2023 – Master 2 Internship « stabilization of Water in Water emulsions by complex core coacervate « 

In collaboration with Theo Merland at SIMM

Water-in-water (W/W) emulsions form when aqueous solutions of two incompatible polymers are mixed, leading to two phases rich in one or the other polymer. They attract more and more interest due to their potential use for encapsulation or compartmentalization, but also in food science. However, contrary to oil/water emulsions, the interface between the two phases is large (few nanometers) and the interfacial tension is much weaker. For these reasons, their stabilization is challenging as it cannot be carried out by the addition of molecular stabilizers such as surfactants. The Pickering effect, consisting of the adsorption of particles at the interface that prevent coalescence, has been proved to be the most efficient way of stabilizing W/W emulsions.1 The particles must be big enough to adsorb at the interface and stabilization is enhanced when they display affinity with at least one of the two phases.2,3

In this context, complex coacervate core micelles (C3Ms) appear as excellent candidates. C3Ms are obtained by co-assembly of polyelectrolytes of opposite charge, forming a nanoscopic complex corresponding to a nanoscopically confined coacervate phase. Their stabilization is ensured by the attachment of a neutral hydrophilic block on at least one of the two polyelectrolytes to form a shell around the coacervate core. The final structures are similar to micelles from amphiphilic block copolymers, however their core is hydrophilic, therefore it is swollen by water. The size and morphology of C3Ms can be tuned by the ratio of neutral to charged units in the diblock copolymer(s), but also by parameters such as pH, salt concentration or temperature.5

We propose the use of these hydrophilic particles as stabilizers in W/W emulsions. They can cover the interface even at low concentration, because of their low density. Additionally, their affinity for both phases can be tuned by a careful choice of repeating units. The ability to tune the morphology of these particles is of great interest, as it is well known that worm-like or lamellar micelles cover the interface more efficiently than spherical micelles. The emulsions will then be destabilized on-demand by applying a trigger that disassembles the C3Ms such as pH or ionic strength.4 The stability of W/W emulsions will be studied by macroscopic observations and Turbiscan® and their microstructure will be studied by confocal microscopy.

Techniques : DLS, Turbiscan®, confocal laser scanning microscopy

3. Références / References

1.         Balakrishnan, G.; Nicolai, T.; Benyahia, L.; Durand, D., Particles Trapped at the Droplet Interface in Water-in-Water Emulsions. Langmuir 2012, 28 (14), 5921-5926.

2. Keal, L., Collosqui, C., Tromp, H., Monteux, C., Physical Review Letters, 2018

3.         Merland, T.; Waldmann, L.; Guignard, O.; Tatry, M.-C.; Wirotius, A.-L.; Lapeyre, V.; Garrigue, P.; Nicolai, T.; Benyahia, L.; Ravaine, V., Thermo-induced inversion of water-in-water emulsion stability by bis-hydrophilic microgels. Journal of Colloid and Interface Science 2022, 608, 1191-1201.

4.         Voets, I. K.; de Keizer, A.; Cohen Stuart, M. A., Complex coacervate core micelles. Advances in Colloid and Interface Science 2009, 147-148, 300-318.

5.         Es Sayed, J.; Brummer, H.; Stuart, M. C. A.; Sanson, N.; Perrin, P.; Kamperman, M., Responsive Pickering Emulsions Stabilized by Frozen Complex Coacervate Core Micelles. ACS Macro Letters 2022, 11 (1), 20-25.