Publications

Lipid nanoparticles, based on nanoemulsion templates, are interesting candidates for contrast agent and active ingredient transport and delivery due to their small size, biodegradable nature and high versatility. An optimized nanosystem for drug delivery should present an important encapsulation ratio, as well as controlled release kinetics. In this context, the influence of the lipid nanoparticle core composition on the encapsulation and release behavior of the Nile Red fluorophore, used as a model molecule of intermediate lipophilicity, is explored. For that purpose, the lipid nanoparticle physical state, the encapsulated molecule localization, and the encapsulation/release behavior are studied. Careful characterization of lipid nanoparticles is performed by DSC and 1H NMR analysis.Nile Red localization is evaluated by complementary fluorescence spectroscopy and 1H NMR techniques. The encapsulation of Nile Red is governed and limited by its solubility in the lipids. A double localization of the fluorophore at the membrane and in the particle core is observed, resulting in a two-phase release kinetics: a quick burst release, followed by a slow prolonged release. Adding wax to the formulation increases the lipid nanoparticle internal viscosity while favoring Nile Red localization in the core, which results in slower release kinetics.

Emulsions have been studied for a long time because of the richness of their related fundamental physicochemical phenomena and owing to their wide industrial applications. The development of microfluidics offers new opportunities to investigate emulsion features and behaviours. This review relates the use of microfluidic tools for probing the interfacial properties of emulsion droplets and the two main mechanisms of destabilisation, namely the coalescence of adjacent drops and the molecular transfer between neighbouring drops.

The incorporation of mineral particles into a polymer matrix leads to extra properties of the polymeric material that are linked to the homogeneity of the mixture. A fine homogeneity can be obtained by using a latex route where the two components are first dispersed in water and then dried. Here, we show a novel way to make an elastomeric composite material via a bulk destabilization of a binary colloidal dispersion. The mixture is composed of a natural rubber latex, which is naturally stabilized, and carbon black particles that are dispersed in water with the help of surfactants. We observe either a transition towards a weak gel, which is a reversible state, or a transition towards an irreversible elastic solid. These structural transitions are mainly controlled by the surfactant concentration that tunes the interaction between natural rubber and carbon black particles, the latter bridging polymer droplets together. We also show that the weak gel can become an irreversible elastic solid under a high shear. This shearinduced heteroaggregation phenomenon exhibits the features of a thermally activated process.

The search for novel organic molecules with biological activity on human, animal, and plant physiological systems has passed through many phases over the centuries. From first steps testing single molecules on whole living systems to fully automated high-throughput screening (HTS) testing tens or hundreds of thousands of molecules per day on purified protein targets, the search has become ever more complex (1, 2). However, the increase in success has not been proportional to the effort and expense entailed. In particular, when considering the screening of “small molecules” (molecular mass <1,000 Da), the results of contemporary HTS have been plagued with problems of false positives, false negatives (3), and the abnormal behavior of certain molecules resulting from their physicochemical properties rather than  their biological activity (4). In PNAS, Miller et al. (5) describe a significant evolution of current HTS technology that increases the confidence in the detection of truly active

Microorganisms are widely used to generate valuable products, and their efficiency is a major industrial focus. Bioreactors are typically composed of billions of cells, and available measurements only reflect the overall performance of the population. However, cells do not equally contribute, and process optimization would therefore benefit from monitoring this intrapopulation diversity. Such monitoring has so far remained difficult because of the inability to probe concentration changes at the single-cell level. Here, we unlock this limitation by taking advantage of the osmotically driven water flux between a droplet containing a living cell toward surrounding empty droplets, within a concentrated inverse emulsion. With proper formulation, excreted products are far more soluble within the continuous hydrophobic phase compared to initial nutrients (carbohydrates and salts). Fast diffusion of products induces an osmotic mismatch, which further relaxes due to slower diffusion of water through hydrophobic interfaces. By measuring droplet volume variations, we can deduce the metabolic activity down to isolated single cells. As a proof of concept, we present the first direct measurement of the maintenance energy of individual yeast cells. This method does not require any added probes and can in principle apply to any osmotically sensitive bioactivity, opening new routes for screening, and sorting large libraries of microorganisms and biomolecules.

Water drops dispersed in chloroform and stabilized with phospholipids become adhesive if a bad solvent for lipids, such as silicone oil, is added to the continuous phase. In this way, two sticking drops are separated by a bilayer of phospholipids. By using microfluidic technologies, we probe the stability and properties of such membranes likewise encountered in foams or vesicles. We first establish the stability diagram of adhering drop pairs as a function of the continuous phase composition. We found two regimes of destabilization of the bilayer. The first one concerns a competition between the dynamics of adhesion and the transport of surfactants toward the interfaces that leads to a dilute surfactant coverage. The second one corresponds to a dense surface coverage where the lifetime distribution of the bilayer exponentially decreases as a signature of a nucleation process. In the stable regime, we observe the propagation of adhesion among a concentrated collection of drops. This is another remarkable illustration of the suction consequence when two close deformable objects are pulled apart. Moreover, the present experimental strategy offers a novel way to study the phase diagrams of bilayers from a single phospholipid to a mixture of phospholipids. Indeed, we detect phase transitions at a liquid−liquid interface that are ruled by the amount of bad solvent. Finally, we probe the transport of water molecules through the bilayer and show that its permeability is linked to the adhesion energy that reflects its fluidity.

Superparamagnetic colloids are used in many studies to apply a force or a torque on biological systems such as cells or DNA molecules. The physical process by which magnetization appears in those beads, allowing them to exert forces, is still poorly understood. In a first part, with an original experimental setup based on optical anisotropy measurements, we show that the apparently magnetically isotropic
beads can orient themselves in a magnetic field. Equilibrium and out of equilibrium measurements allowed ,to develop a model explaining how a few big grains in the beads are responsible for the whole coupling. The robustness of this model lies in its generalization to several sizes of beads and its consistency with the properties of the ferrofluid used to make them. In a second part, the reaction of a few actin filaments to the pressure applied by superparamagnetic colloids is studied. This setup represents a direct way to probe the physical mechanism underlying the production of force by actin filaments polymerization in cellular motility. Controlling the filaments’ organization allows to study two ideal ideal situations. We experimentally show that in the former situation the polymerization velocity is independent of the applied force. This is no longer true in the latter situation where the filaments are verys ti. Thus, we experimentally show for the first time the eect of force on actin filaments polymerization. A Brownian ratchet based numerical model with no load sharing can describe the production of force in that case.