Platelets production in microfluidic bioreactors

Platelets are small blood cells that prevent bleeding. They are formed by fragmentation of precursor cells called megakaryocytes (MK). In vivo, this process, called thrombopoiesis, starts in the bone marrow, where mature MK reside and extend long cytoplasmic branches into the sinusoidal blood capillaries. Aided by the bloodstream, the tips of these extensions are released in the circulation and undergo fissions that produce platelets. We developed a microfluidic bioreactor to produce platelets from MK in vitro. MK are trapped inside a microfluidic chamber. Then, a high shear stress is imposed to elongate and rupture the cells into platelets. This work is supported by Hauts de France region and the FEDER funds (2014-2020)

Particles-induced fingering instability

Interfacial two-phase flows are critical in many natural and industrial processes, including flows in porous media, petroleum extraction, and microfluidic two-phase flow. An instability of the interface, known as the Saffman-Taylor instability, can occur when a low viscosity fluid displaces one of higher viscosity. It results from the decrease of the flow resistance as the fluid of lower viscosity replaces the more viscous one. While the inverse situation is generally stable, we show in this study that the presence of microparticles on the walls can modify this equilibrium and leads to the generation of finger patterns. Such process might occur naturally in cleaning processes where bacteria, spores, dust or particles are present on surfaces and dramatically affect the underlying dynamics.

Flow focusing of two miscible fluids in a microfluidic junction

When a liquid is injected into another surrounding liquid, it is called flow focusing or co-flow. This can be used to create fibers, droplets or to align micro particles or cells. We experimentally investigate the influence of imposing pressure to generate co-flow in a cross-junction microfluidic device. A state diagram is constructed. Furthermore, we characterize the jet width as a function of the viscosity contrast, the inlet pressures, the flow rates and the channel aspect ratio. This study defines the conditions needed to create a co-flow regime with a specific jet width using a pressure driven flow.

Vibration of cylindrical armoured bubble

When a bubble is covered with a monolayer of particles, it is called armoured bubble. A microfluidic technique has been developed to create cylindrical bubbles covered by a monolayer of microparticles. We studied the dynamic response of bubbles to vertical mechanical vibration. A reduction of the bubble surface has been observed by the dissemination of the excess particles in the liquid. This study opens perspectives to the localized dissemination of pharmacological agents in the body.

Motion of an ellipsoid particle in the vicinity of a wall

The dynamics of an ellipsoid particle in the vicinity of a wall is of major interest for biological and industrial applications. For example, the motion of microorganisms like Bactria or Biofilms  before and after adhering to a wall, or the motion of platelets in our vessels. Therefore, we studied numerically this motion. Elongate ellipsoids (rugby ball) and flattened ellipsoids (platelets) were studied in a non-inertial flow at low concentrations. We developed a numerical code based on the Boundary Elements Method (BEM). Our results give a complete picture of the dynamics of an ellipsoid particle over a wide range of aspect ratio, orientation and wall distance.

Effect of drying on the resistance to detachment of Bacillus spores

The agro-food industry is facing recurring problems of bacteria and biofilm adhesion (e.g., Escherichia coli, Listeria, Bacillus cereus spores, Bacillus subtilis) at the walls of food production lines. These microorganisms are largely subject to a drying step prior to their adhesion. Thus, we studied the consequences of the drying conditions on the resistance of three types of spores (bacteria) as well as micro-beads. A drying step on glass slides at different temperatures and duration was made before flowing water in a microfluidic chip to detach them. We have shown in this study that there is an effect of the duration and the temperature of the drying on the resistance to detachment.

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