CFD analysis and experimental validation of magnetic droplet generation and deflection across multilaminar flow streams

J. Gómez-Pastora, I.H. Karampelas, M.D. Tarn, E. Bringas, A. Iles, N. Pamme, E.P. Furlani, I. Ortiz
University of Cantabria,

Keywords: magnetic droplets, multilaminar flow microfluidic systems, CFD modeling, droplet generation, droplet deflection, J number


The use of droplet-based microfluidic systems has increased in the last decade due to the advantages these systems present, such as compatibility with many chemical and biological reagents, capability of performing a variety of “digital fluidic” operations that can be rendered programmable and reconfigurable, decreased reaction times and large interfacial areas, repeatability of operations, etc. However, with the maturity of this platform technology, sophisticated and delicate control of droplet generation and manipulation is needed to address increasingly complex applications. Magnetic separation has proven a useful and elegant method for manipulating magnetic materials in microfluidic devices. In this work, we demonstrate that multilaminar flow droplet processing using magnetic fields is a versatile high throughput platform for biomedical research. In this work, we present a CFD model to study the continuous processing of droplets by deflecting ferrofluid-based templates through multilaminar flow streams. We introduce different chip designs and an optimization study for the generation and manipulation of droplets by applying magnetic fields generated by a permanent magnet. The numerical method includes the integration of magnetic and fluidic computational models that accurately describe the droplet generation and motion under different magnetic field and flow conditions. The CFD is performed using the volume-of-fluid (VOF) method as implemented in FLOW-3D. The flow solver was linked to a FORTRAN subroutine that calculates the magnetic field due to the magnet and the corresponding magnetic force exerted on the droplets. For optimization purposes, a dimensionless number J that describes the ratio between magnetic and fluidic forces is introduced. The impact of different process variables and parameters - flowrates, magnet location and chip design - on both droplet size and trajectory, is quantified. Finally, experimental validation of the model is carried out with oil-based ferrofluid droplets and ink aqueous solutions. Theoretical and experimental results are accordingly compared and discussed. Due to the unique advantages of integrating magnetic materials within droplet microfluidics, this technology has the potential to provide novel solutions to different biomedical engineering challenges for advanced diagnostics and therapeutics.