A new way to measure viscosity in droplet-based microfluidics for high throughput analysis.

In this work, we propose a new way to measure the viscosity of samples in a microfluidic device. By analysing the shape of droplets after an expansion, we can measure the viscosity of the phase inside the droplet knowing the surface tension between the two liquids, the flow rate, the geometry of the channel and the viscosity of the continuous phase. This work paves the way for future high throughput studies in the framework of digital microfluidics.

Ultralow Interfacial Tension Measurement through Jetting/Dripping Transition.

In this paper, we present a dynamic microfluidic tensiometer able to perform measurements over more than four decades and which is suitable for high throughput experimentations. This tensiometer is able to withstand hard conditions such as high pressure, high temperature, high salinity, and crude oil. It is made of two coaxial capillaries in which two immiscible fluids are injected. Depending on the flow rate of each phase, either droplets or jetting will be obtained. The transition between these two regimes relies on the Rayleigh-Plateau instability. This transition can be theoretically computed thanks to a linear analysis based on the convective and absolute instabilities theory. From this model, the interfacial tension between the two phases can be calculated.

Surface photografting of acrylic acid on poly(dimethylsiloxane). Experimental and dissipative particle dynamics studies.

This work includes both experimental and theoretical studies of the wetting property changes of water on a surface of poly(dimethylsiloxane) (PDMS) modified with different amounts of acrylic acid (AA). The default surface properties of PDMS were changed from hydrophobic to hydrophilic behavior which was characterized with contact angle measurements by two approaches: (i) experimental tests of samples subjected to a photografting polymerization procedure to obtain a functionalized surface and (ii) DPD (dissipative particle dynamics) simulations which also involve the calculation of sets of repulsive parameters determined following two methods: the use of the "Blends" module in the Materials Studio software and the calculation of cohesive energy density with molecular simulations. Changes of contact angle values observed from both experimental and numerical simulation results provide qualitative and quantitative information on the wetting behavior of photografted surfaces.

Ultrasound internal tattooing.

PURPOSE: The ability of remotely tagging tissues in a controlled and three-dimensional manner during preoperative imaging could greatly help surgeons to identify targets for resection. The authors' objective is to selectively and noninvasively deposit markers under image guidance for such internal tattooing. METHODS: This study describes the production of new ultrasound-inducible droplets carrying large payloads of fluorescent markers and the in vivo proof of concept of their remote and controlled deposition via focused ultrasound. The droplets are monodispersed multiple emulsions produced in a microfluidic system, consisting of aqueous fluorescein in perfluorocarbon in water. Their conversion (either by vaporization or cavitation) is performed remotely using a clinical ultrasonic imaging probe. RESULTS: When submitted to 5 MHz imaging pulses, the droplets vaporize in vitro at 1.4 MPa peak-negative pressure and eject their content. After several seconds, a brightly fluorescent spot (0.5 mm diameter) is observed at the focus of the transducer. Experiments in the chorioallantoique membrane of chicken eggs and chicken embryo demonstrate that the spot is stable and is easily seen by naked eye. CONCLUSIONS: These ultrasound-inducible multiple emulsions could be used to deliver large amounts of contrast agents, chemotherapy, and genetic materials in vivo using a conventional ultrasound scanner.

Monodisperse colloids synthesized with nanofluidic technology.

Limitations in the methods employed to generate micrometric colloidal droplets hinder the emergence of key applications in the fields of material science and drug delivery. Through the use of dedicated nanofluidic devices and by taking advantage of an original physical effect called capillary focusing, we could circumvent some of these limitations. The nanofluidic (i.e., submicrometric) devices introduced herein are made of soft materials, and their fabrication relies upon rapid technologies. The objects that we have generated are simple droplets, multiple droplets, particles, and Janus particles whose sizes lie between 900 nm and 3 microm (i.e., within the colloidal range). Colloidal droplets have been assembled on-chip into clusters and crystals, yielding discrete diffraction patterns. We illustrate potential applications in the field of drug delivery by demonstrating the ability of multiple droplets to be phagocytosed by murine macrophage-type cells.

Synthesizing microcapsules with controlled geometrical and mechanical properties with microfluidic double emulsion technology.

Using lithography-based microfluidic technology, we produce monodisperse single-core microcapsules with UV-cured TPGDA (triprophylene glycol diacrylate) shells. We show that the geometrical and mechanical characteristics of the microcapsules can be predicted on a quantitative basis and tuned by varying the flow conditions. Shell thicknesses are varied by changing the flow rates of the inner or intermediate phases, according to mass conservation constraint. Off-centering of the core with respect to the shell is controlled by varying the shell phase viscosity. The mechanical properties of the capsules can be varied by changing the flow conditions and are quantitatively predicted by a numerical simulation. The simulation moreover provides a correct qualitative description of their rupture. As a whole, the work carried out in the present paper shows, on a quantitative basis, that microfluidic technology allows to finely control the geometrical and mechanical properties of microcapsules generated on chip. The level of control we reach here is not accessible, by far, to conventional technologies. Combined with parallelization, the present work opens routes toward the production of novel families of monodisperse microcapsules with tunable properties.

Equilibrium and nonequilibrium states in microfluidic double emulsions.

We describe experimental and theoretical studies dedicated to establishing the physics of formation of double droplets in microfluidic systems. We show that the morphologies (complete engulfing, partial engulfing, and nonengulfing) obtained at late times minimize the interfacial energy of the system. We explain that nonequilibrium morphologies generated in the system can have long lifetimes. Remarkably, the physics of formation of the double droplets with microfluidics allows the synthesis of particles with new morphologies.