Trapping microfluidic drops in wells of surface energy

International audienceA small hole etched in the top of a wide microchannel creates a well of surface energy for a confined drop. This produces an attractive force F ? equal to the energy gradient, which is estimated from geometric arguments. We use the drag Fd from an outer flow to probe the trapping mechanism. When Fd < F?, the drop deforms but remains anchored to the hole. Its shape provides information about the pressure field. At higher flow velocities, the drop detaches, defining a critical capillary number for which Fd=F?. The measured anchoring force agrees with the geometric model. © 2011 American Physical Society

Microfluidique de gouttes 2D par gradient de confinement

Over the last decade, the field of droplet microfluidics has built upon the concept of droplet microreactors, i.e. the idea that a drop can be used to collect, carry and characterize chemicals, biological systems or genetic material. Although droplet microfluidics promises to miniaturize and automate standard microtiter plates on-a-chip, the field has remained dominated by a serial mindset which contrasts with the inherent 2D format of the microtiter plate. This manuscript provides a novel strategy for droplet management that allows for droplet microfluidics to be implemented easily inside 2D chambers. To do so, it relies on confinement gradients to apply forces on the droplets.L'usage de gouttes comme microréacteurs movite le développement rapide de la microfluidique de gouttes. En effet, une goutte peut être utilisée pour collecter, transporter et analyser du matériel chimique, biologique ou génétique. Ainsi, la microfluidique de goutte porte la promesse d'une miniaturisation et d'une automatisation sur puce des process actuellement mis oeuvre sur microplaques. Toutefois, l'architecture des dispositifs reste essentiellement sérielle et en opposition avec le format intrinsèquement 2D des microplaques. Ce travail de thèse fournit une nouvelle stratégie de gestion de gouttes sur puce qui permet d'implémenter des procédés de microfluidiques de goutte au sein de chambres bidimensionnelles. Les méthodes mises au point emploient des gradients de confinement pour agir sur les gouttes

Microfluidique de gouttes 2D par gradient de confinement

L'usage de gouttes comme microréacteurs movite le développement rapide de la microfluidique de gouttes. En effet, une goutte peut être utilisée pour collecter, transporter et analyser du matériel chimique, biologique ou génétique. Ainsi, la microfluidique de goutte porte la promesse d'une miniaturisation et d'une automatisation sur puce des process actuellement mis oeuvre sur microplaques. Toutefois, l'architecture des dispositifs reste essentiellement sérielle et en opposition avec le format intrinsèquement 2D des microplaques. Ce travail de thèse fournit une nouvelle stratégie de gestion de gouttes sur puce qui permet d'implémenter des procédés de microfluidiques de goutte au sein de chambres bidimensionnelles. Les méthodes mises au point emploient des gradients de confinement pour agir sur les gouttesOver the last decade, the field of droplet microfluidics has built upon the concept of droplet microreactors, i.e. the idea that a drop can be used to collect, carry and characterize chemicals, biological systems or genetic material. Although droplet microfluidics promises to miniaturize and automate standard microtiter plates on-a-chip, the field has remained dominated by a serial mindset which contrasts with the inherent 2D format of the microtiter plate. This manuscript provides a novel strategy for droplet management that allows for droplet microfluidics to be implemented easily inside 2D chambers. To do so, it relies on confinement gradients to apply forces on the dropletsPALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Dynamics of microfluidic droplets

International audienceThis critical review discusses the current understanding of the formation, transport, and merging of drops in microfluidics. We focus on the physical ingredients which determine the flow of drops in microchannels and recall classical results of fluid dynamics which help explain the observed behaviour. We begin by introducing the main physical ingredients that differentiate droplet microfluidics from single-phase microfluidics, namely the modifications to the flow and pressure fields that are introduced by the presence of interfacial tension. Then three practical aspects are studied in detail: (i) The formation of drops and the dominant interactions depending on the geometry in which they are formed. (ii) The transport of drops, namely the evaluation of drop velocity, the pressure-velocity relationships, and the flow field induced by the presence of the drop. (iii) The fusion of two drops, including different methods of bridging the liquid film between them which enables their merging. © 2010 The Royal Society of Chemistry

Microchannel deformations due to solvent-induced PDMS swelling

International audienceThe compatibility of polydimethylsiloxane (PDMS) channels with certain solvents is a well known problem of soft lithography techniques, in particular when it leads to the swelling of the PDMS blocks. However, little is known about the modification of microchannel geometries when they are subjected to swelling solvents. Here, we experimentally measure the deformations of the roof of PDMS microchannels due to such solvents. The dynamics of impregnation of the solvents in PDMS and its relation to volume dilation are first addressed in a model experiment, allowing the precise measurement of the diffusion coefficients of oils in PDMS. When Hexadecane, a swelling solvent, fills a microchannel 1 mm in width and 50 µm in height, we measure that the channel roof bends inwards and takes a parabolic shape with a maximum deformation of 7 µm. The amplitude of the subsidence is found to increase with the channel width, reaching 28 µm for a 2 mm wide test section. On the other hand, perfluorinated oils do not swell the PDMS and the microchannel geometry is not affected by the presence of perfluorodecalin. Finally, we observe that the trajectories of droplets flowing in this microchannel are strongly affected by the deformations: drops carried by swelling oils are pushed towards the edges of the channel while those carried by non-swelling oils remain in the channel center. © The Royal Society of Chemistry 2010

Droplet microfluidics driven by gradients of confinement

International audienceThe miniaturization of droplet manipulation methods has led to drops being proposed as microreactors in many applications of biology and chemistry. In parallel, microfluidic methods have been applied to generate monodisperse emulsions for applications in the pharmaceuticals, cosmetics, and food industries. To date, microfluidic droplet production has been dominated by a few designs that use hydrodynamic forces, resulting from the flowing fluids, to break drops at a junction. Here we present a platform for droplet generation and manipulation that does not depend on the fluid flows. Instead, we use devices that incorporate height variations to subject the immiscible interfaces to gradients of confinement. The resulting curvature imbalance along the interface causes the detachment of monodisperse droplets, without the need for a flow of the external phase. Once detached, the drops are self-propelled due to the gradient of surface energy. We show that the size of the drops is determined by the device geometry; it is insensitive to the physical fluid properties and depends very weakly on the flow rate of the dispersed phase. This allows us to propose a geometric theoretical model that predicts the dependence of droplet size on the geometric parameters, which is in agreement with experimental measurements. The approach presented here can be applied in a wide range of standard applications, while simplifying the device operations. We demonstrate examples for single-droplet operations and high-throughput generation of emulsions, all of which are performed in simple and inexpensive devices

Rails and anchors: Guiding and trapping droplet microreactors in two dimensions

International audienceThis paper presents a method to control the motion of nanolitre drops in a wide and thin microchannel, by etching fine patterns into the channel's top surface. Such control is possible for drops that are squeezed by the channel roof, by allowing them to reduce their surface energy as they enter into a local depression. The resulting gain in surface energy pulls a drop into the groove such that localized holes can be used as anchors for holding drops, while linear patterns can be used as rails to guide them along complex trajectories. An anchored drop can remain stationary indefinitely, as long as the driving flow rate is below a critical value which depends on the hole and drop sizes. By micro-fabricating holes into a grid pattern, drops can be arrayed and held in the observation field of a microscope against the mean carrier flow. Their contents can then be modulated by gas exchange with the flowing carrier oil. We demonstrate in particular how the pH or the oxygen levels within the drops can be controlled spatially and temporally, either by exposing rows of drops to two streams of oil at different gas concentrations or by periodically switching oil inputs to vary the gas concentration of drops as a function of time. Oxygen control is used to selectively deoxygenate droplets that encapsulate red blood cells from patients suffering from sickle cell disease, in order to study the polymerization of intracellular hemoglobin. Cycles of oxygenation and deoxygenation of anchored droplets induce depolymerization and polymerization of the hemoglobin, thus providing a method to simulate the cycling that takes place in physiological flows. Cop. 2011 The Royal Society of Chemistry

Procédé microfluidique de traitement et d'analyse d'une solution contenant un matériel biologique, et circuit microfluidique correspondant

La présente invention a pour objet un procédé microfluidique de traitement et d'analyse d'une solution contenant un matériel biologique, comprend une étape d'introduction de la solution dans des microcanaux d'un circuit microfluidique (1), une étape de formation de gouttes de cette solution, sous l'effet de modifications de la tension de surface de la solution, une étape de déplacement des gouttes vers une ou plusieurs zone de stockage de gouttes (130), sous l'effet de modifications de la tension de surface des gouttes, une étape de traitement des gouttes et une étape d'analyse des gouttes