Publications

Studies of the dynamics of the antibody-mediated immune response have been hampered by the absence of quantitative, high-throughput systems to analyze individual antibody-secreting cells. Here we describe a simple microfluidic system, DropMap, in which single cells are compartmentalized in tens of thousands of 40-pL droplets and analyzed in two-dimensional droplet arrays using a fluorescence relocation-based immunoassay. Using DropMap, we characterized antibody-secreting cells in mice immunized with tetanus toxoid (TT) over a 7-week protocol, simultaneously analyzing the secretion rate and affinity of IgG from over 0.5 million individual cells enriched from spleen and bone marrow. Immunization resulted in dramatic increases in the range of both single-cell secretion rates and affinities, which spanned at maximum 3 and 4 logs, respectively. We observed differences over time in dynamics of secretion rate and affinity within and between anatomical compartments. This system will not only enable immune monitoring and optimization of immunization and vaccination protocols but also potentiate antibody screening

doi:10.1038/nbt.3964

access to a view-only version  http://rdcu.be/vKeI

We report on the impact of surface hydrophobization on the structure of aqueous silica dispersions and how this structure resists drying stress. Hydrophilic silica particles were hydrophobized directly in water using a range of organosilane precursors, with a precise control of the grafting density. The resulting nanostructure was precisely analyzed by a combination of small-angle X-ray scattering (SAXS) and cryo-microscopy (cryo-TEM). Then, the dispersion was progressively concentrated by drying, and the evolution of the nanostructures as a function of the grafting density was followed by SAXS. At the fundamental level, because the hydrophobic character of the silica surfaces could be varied continuously through a precise control of the grafting density, we were able to observe how the hydrophobic interactions change particles interactions and aggregates structures. Practically, this opened a new route to tailor the final structure, the residual porosity, and the damp-proof properties of the fully dried silica. For example, regardless of the nature of the hydrophobic precursor, a grafting density of 1 grafter per nm² optimized the interparticle interactions in solution in view to maximize the residual porosity in the dried material (0.9 cm³/g) and reduced the water uptake to less than 4% in weight compared to the typical value of 13% for hydrophilic particles (at T = 25 °C and relative humidity = 80%).

DOI: 10.1021/acs.langmuir.6b04505

Aluminium salts are widely used to control sweating for personal hygiene purposes. Their mechanism of
action as antiperspirants was previously thought to be a superficial plugging of eccrine sweat pores by
the aluminium hydroxide gel. Here we present a microfluidic T junction device that mimics sweat ducts,
and is designed for the real time study of interactions between sweat and ACH (Aluminium Chloro
Hydrate) under conditions that lead to plug formation. We used this device to image and measure the
diffusion of aluminium polycationic species in sweat counter flow. We report the results of small angle
X-ray scattering experiments performed to determine the structure and composition of the plug, using
BSA (Bovine Serum Albumin) as a model of sweat proteins. Our results show that pore occlusion occurs
as a result of the aggregation of sweat proteins by aluminium polycations. Mapping of the device shows
that this aggregation is initiated in the T junction at the location where the flow of aluminium
polycations joins the flow of BSA. The mechanism involves two stages: (1) a nucleation stage in which
aggregates of protein and polycations bind to the wall of the sweat duct and form a tenuous
membrane, which extends across the junction; (2) a growth stage in which this membrane collects
proteins that are carried by hydrodynamic flow in the sweat channel and polycations that diffuse into
this channel. These results could open up perspectives to find new antiperspirant agents with an
improved efficacy.

DOI: 10.1039/c6sm02510b

We report on a measurement of forces between particles adsorbed at a water–oil interface in the presence of an oil-soluble polymer. The cationic polymer interacts electrostatically with the negatively charged particles, thereby modulating the particle contact angle and the magnitude of capillary attraction between the particles. However, polymer adsorption to the interface also generates an increase in the apparent interfacial viscosity over several orders of magnitude in a time span of a few hours. We have designed an experiment in which repeated motion trajectories are measured on pairs of particles. The experiment gives an independent quantification of the interfacial drag coefficient (10–7–10–4 Ns/m) and of the interparticle capillary forces (0.1–10 pN). We observed that the attractive capillary force depends on the amount of polymer in the oil phase and on the particle pair. However, the attraction appears to be independent of the surface rheology, with changes over a wide range of apparent viscosity values due to aging. Given the direction (attraction), the range (∼μm), and the distance dependence (∼1/S5) of the observed interparticle force, we interpret the force as being caused by quadrupolar deformations of the fluid–fluid interface induced by particle surface roughness. The results suggest that capillary forces are equilibrated in the early stages of interface aging and thereafter do not change anymore, even though strong changes in surface rheology still occur. The described experimental approach is powerful for studying dissipative as well as conservative forces of micro- and nanoparticles at fluid–fluid interfaces for systems out of equilibrium.

DOI: 10.1021/acs.langmuir.6b03910

Liquid core capsules having a hydrogel membrane are becoming a versatile tool for three- dimensional culture of micro-organisms and mammalian cells. Making sub-millimeter capsules at a high rate, via the breakup of a compound jet in air, opens the way to high throughput screen- ing applications. However, a control of the capsule size monodispersity, especially required for quantitative bioassays, was still lacking. Here, we report how the understanding of the underlying hydrodynamic instabilities that occur during the process can lead to calibrated core-shell biore- actors. This implies: i) to damp the shear layer instability that develops inside the injector arising from the co-annular flow configuration of liquid phases having contrasted viscoelastic properties; ii) to control the capillary instability of the compound jet by superposing a harmonic perturbation to the shell flow; iii) to avoid coalescence of drop during jet fragmentation as well as during drop flight towards the gelling bath, and iv) to ensure a proper engulfment of the compound drops into the gelling bath for building a closed hydrogel shell. We end up with the creation of numerous identical compartments in which cells are able to form mutlicellular aggregates, namely spheroids. In addition, we implement an intermediate composite hydrogel layer, composed of alginate and collagen, allowing cell adhesion and thus the formation of epithelia or monolayers of cells.