An integrated detection method for flow viscosity measurements in microdevices

Angeles Ivon Rodriguez-Villarreal, Laura Ortega Taña, Joan Cid, Aurora Hernández-Machado, Tomas Alarcon, Pere Miribel-Catala, Jordi Colomer-Farrarons


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Normalization of blood viscosity according to the hematocrit and the biomechanical properties of red blood cells

C. Trejo-Soto, A. Hernández-Machado


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The long cross-over dynamics of capillary imbibition

E. Ruiz-Gutierrez, S. Armstrong, S. Leveque, C. Michel, I. Pagonabarraga, G. G. Wells, A. Hernández-Machado, R. Ledesma-Aguilar


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A biomechanical strategy to control bacterial proliferation

S. Salinas-Almaguer, M. Mell, V.G. Almenro-Vedia, J.C. Ruiz-Suarez, F. Monroy, T. Alarcon, R. A. Barrio, A. Hernández-Machado


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Fluid front advance in hydrophilic structured micro channels

I.Domínguez-Roman, R.A. Barrio A. Hernández-Machado


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The dynamics of shapes of vesicles membranes with time dependent spontaneous curvature

R.A. Barrio, T. Alarcon, A. Hernández-Machado

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We study the time evolution of the shape of a vesicle membrane under time-dependent spontaneous curvature by means of phase-field model. We introduce the variation in time of the spontaneous curvature via a second field which represents the concentration of a substance that anchors with the lipid bilayer thus changing the local curvature and producing constriction. This constriction is mediated by the action on the membrane of an structure resembling the role of a Z ring. Our phase-field model is able to reproduce a number of different shapes that have been experimentally observed. Different shapes are associated with different constraints imposed upon the model regarding conservation of membrane area. In particular, we show that if area is conserved our model reproduces the so-called L-form shape. By contrast, if the area of the membrane is allowed to grow, our model reproduces the formation of a septum in the vicinity of the constriction. Furthermore, we propose a new term in the free energy which allows the membrane to evolve towards eventual pinching.

Coaxial flow focusing microfluidic devices: Experiments and theory

R. Rodriguez-Trujillo, Y-H. Kim-Im, A. Hernández-Machado

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A coaxial flow focusing PDMS (polydimethylsiloxane) microfluidic device has been designed and manufactured by soft lithography in order to experimentally study a miscible inner flow. We studied a coaxially focused inner flow (formed by an aqueous fluorescein solution) which was fully isolated from all microchannel surfaces by an additional water outer flow. Different flow rates were used to produce a variety of flow ratios and a 3D reconstruction of the cross-section was performed using confocal microscope images. The results showed an elliptical section of the coaxially focused inner flow that changes in shape depending on the flow rate ratio applied. We have also developed a mathematical model that allows us to predict and control the geometry of the coaxially focused inner flow.

Enhanced imbibitions from cooperation between wetting and inertia via pulsatile forcing

J. Flores Gerónimo , A. Hernández-Machado E. Corvera Poire

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We study the dynamics of microfluidic interfaces driven by pulsatile pressures in the presence of neutral and hydrophilic walls. For this, we propose a new phase field model that takes inertia into account. For neutral wetting, the interface dynamics is characterized by a response function that depends on a non-dimensional frequency, which involves the time scale associated with inertia. We have found a regime, for large values of this non-dimensional frequency, in which inertia is relevant, and our model is necessary for a correct description of the dynamics. For hydrophilic walls, the dynamics of the contact line with pulsatile forcing is basically undistinguishable to the dynamics of imbibition solely due to wetting. However, we observe that the presence of inertia causes the interface to advance faster than in the absence of pulsatile forcing. This is because pulsatile forcing induces inertia at the bulk to cooperate with wetting creating an enhancement of the imbibition process. We characterize this complex dynamics with transitory exponents that, at early times, are larger than the Washburn ones, and tend to the Washburn exponent at long times, when the interface feels less and less the driving force applied at the entrance of the microchannel, and the dynamics is dominated solely by wetting.

Collective behavior of red blood cells in confined channels

G.R. Lazaro, A. Hernández-Machado, I. Pagonabarraga

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We study the flow properties of red blood cells in confined channels, when the channel width is comparable to the cell size. We focus on the case of intermediate concentrations when hydrodynamic interactions between cells play a dominant role. This regime is different to the case of low concentration in which the cells behave as hydrodynamically isolated. In this last case, the dynamic behavior is entirely controlled by the interplay between the interaction with the wall and the elastic response of the cell membrane. Our results highlight the different fluid properties when collective flow is present. The cells acquire a characteristic slipper shape, and parachute shapes are only observed at very large capillary numbers. We have characterized the spatial ordering and the layering by means of a pairwise correlation function. Focusing effects are observed at the core of the channel instead of at the lateral position typical of the single-train case. These results indicate that at these intermediate concentrations we observed at the microscale the first steps of the well-known macroscopic Fahraeus-Lindqvist effect. The rheological properties of the suspension are studied by means of the effective viscosity, with an expected shear-thinning behavior. Two main differences are obtained with respect to the single-train case. First, a large magnitude of the viscosity is obtained indicating a high resistance to flow. Secondly, the shear-thinning behavior is obtained at larger values of the capillary number respect to the single-train case. These results suggest that the phenomena of ordering in space and orientation occur at higher values of the capillary number.

Front Microrheology of Biological Fluids

C. Trejo-Soto, E. Costa-Miracle, I. Rodríguez-Villarreal, J. Cid, M. Castro, T. Alarcón, A. Hernández-Machado

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We present a study of front microrheology through the development of a microfluidic device and method that describes accurately the non-linear rheology of blood, by means of a simple optical detection method based on tracking the fluid-air interface moving inside a microchannel. We study the behavior of Newtonian fluids of different viscosities and densities, as well, we performed measures for blood at different red blood cells concentration and at different days from its extraction. We have developed a scaling method which allows us to determine a relation between the red blood cell properties at different days from its extraction, according to the agreggation properties of red blood cell. Our results have been compared with theoretical and bibliographical results, which shows realiable results with an error around 6%. In general, our device and method is usefull as a viscometer and rheometer, as well as, it enables to establish a relation between blood viscosity and its red blood cells characteristics.