J. Gómez-Pastora, I.H. Karampelas, E. Bringas, E.P. Furlani, I. Ortiz*University of Cantabria,Spain*

Keywords: magnetic bead separation, two-phase liquid-liquid microfluidic systems, fluid-particle coupling, CFD modeling, J number, blood detoxification

Summary:

The use of magnetic particles has recently expanded for a process known as detoxification in which different toxins and microorganisms are captured from the bloodstream of septic patients. Magnetic particle-based detoxification has been successfully applied for the removal of different toxins and microorganisms from living animals. Due to the magnetic properties of the particles, once the capture of the pathogens is complete, their separation from the patient’s blood can be performed in a continuous process using an external magnetic field provided by rare-earth magnets. Among the many microfluidic magnetic separators that have been proposed in this decade for recovering beads from biological fluids, continuous-flow systems are the most efficient due to their high separation efficacy and throughput. Due to the laminar flow regime developed in microfluidic devices, the separation of particles can be carried out in a continuous operation mode by using two colaminar streams flowing in parallel branches inside the device. Nevertheless, their optimization has been relatively less studied and rational design is often lacking because of the complexity associated to their mathematical description. In this work, we introduce a design for a two-phase continuous-flow microseparator and present an optimization study for the separation of magnetic beads using state-of-the-art computational modeling. The developed numerical method includes a combination of magnetic and fluidic computational models that accurately describe the bead magnetophoretic motion. The model was solved using the finite-volume method with the FLOW-3D solver which was linked to a Fortran code that calculated the magnetic fields and forces. To the best of our knowledge, this is the first computational study of the interaction between two different fluids flowing simultaneously in the device that takes into account two-way coupled particle-fluid interactions in the flow field as well as the effects of the particle motion as they cross the interface between the fluids under various magnetic field intensities. For optimization purposes, a dimensionless number J that describes the ratio between magnetic and fluidic forces is introduced. Finally, the experimental validation of the model is evaluated by fluorescence microscopy with aqueous solutions of fluorescein and magnetic particles functionalized with fluorophores. Theoretical and experimental results are accordingly compared and discussed.