In this study, we explore and model the behavior of a prototype microfluidic device which employs two nonmixing fluids (sheath and inlet fluids) displaying an asymmetric focused flow, in the presence of a fluorescent dye. Fluorescence correlation spectroscopy is employed, allowing the precise measure of flow speeds across the channels and of the concentration profile of the central focused flux along the flow direction. The system is modeled via a standard Navier-Stokes finite-element approach, coupled to convection-diffusion equations for the solute. Simulations reproduce accurately the shape, the position, and the width of the velocity and concentration profiles along the central channel and across the transversal and vertical sections of the microfluidic device. The observed asymmetric flow with respect to the center of the channel is reproduced numerically with an error in the position determination smaller than 1%.
"The internal dimensions of the device, suitable for cell culture, were 4 cm length, 2 mm width and 150 µm height. They were determined through the 3D reconstruction of confocal z-stack images of the channel filled with a fluorescein solution.15 "
[Show abstract][Hide abstract] ABSTRACT: Microfluidic, the technology that manipulates small amount of fluids in microscale complex devices, has undergone a remarkable development during the last decade, by targeting a significant range of applications, including biological tests and single-cell analysis, and by displaying many advantages such as reduced reagent consumption, decreased costs and faster analysis. Furthermore, the introduction of microfluidic tools has revolutionized the study of vascular functions, because the controlled three-dimensional environment and the continuous perfusion provided by the microdevice allow simulating the physiological characteristics of the circulatory system. Researchers interested in the study of vascular physiology, however, are often hampered by the difficulty in handling reduced number of cells after growth in these devices. This work shows how to apply different protocols commonly used in biology, such as the immunofluorescence technique, to cells grown in reversibly-bound microfluidic devices, obtaining results comparable to those retrieved under static conditions in multiwells. In this way, we are able to combine the advantages of microfluidic, i.e., application of continuous flow and shear stress, with classical protocols for the study of endothelial cells.
European journal of histochemistry: EJH 04/2014; 58(2):2360. DOI:10.4081/ejh.2014.2360 · 2.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: One of the most promising way to exploit microfluidic systems is as microreactors. A microreactor can be considered as a microchamber where chemical reactions take place, aimed at the synthesis of novel materials with controlled experimental conditions. The main goal is to reach the highest efficiency towards the desired output product. Mixing is usually very slow in microchannels, when laminar flow conditions characterized by low Reynolds numbers (below 3000) are applied. Many different strategies can be proposed to enhance mixing. In this work we explore and model the behavior of microreactor prototypes having different geometry and aimed at the improvement of mixing efficiency. These prototypes exploit either the hydrodynamic focusing effect or the presence of microstructuration inside the microchannel. In the first case, the focusing effect is used to reduce the diffusion distance between the molecules flowing in the reactors. In the second approach, we explore the influence of lateral steps fabricated inside the channels on the mixing efficiency. The behavior of fluid features is numerically modeled via Navier-Stokes equations coupled to convection-diffusion equations. Moreover, fluorescence based techniques are used to characterize the mixing efficiency in the experimental devices.
La Houille Blanche 09/2011; DOI:10.1051/lhb/2011044 · 0.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Microreactors experience significant deviations from plug flow due to the no-slip boundary condition at the walls of the chamber. The development of stagnation zones leads to widening of the residence time distribution at the outlet of the reactor. A hybrid design optimization process that combines modeling and experiments has been utilized to minimize the width of the residence time distribution in a microreactor. The process was used to optimize the design of a microfluidic system for an in vitro model of the lung alveolus. Circular chambers to accommodate commercial membrane supported cell constructs are a particularly challenging geometry in which to achieve a uniform residence time distribution. Iterative computational fluid dynamics (CFD) simulations were performed to optimize the microfluidic structures for two different types of chambers. The residence time distributions of the optimized chambers were significantly narrower than those of non-optimized chambers, indicating that the final chambers better approximate plug flow. Qualitative and quantitative visualization experiments with dye indicators demonstrated that the CFD results accurately predicted the residence time distributions within the bioreactors. The results demonstrate that such a hybrid optimization process can be used to design microreactors that approximate plug flow for in vitro tissue engineered systems. This technique has broad application for optimization of microfluidic body-on-a-chip systems for drug and toxin studies.
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