(513a) Analysis of Magnetic Bead Separation in Continuous-Flow Magnetophoretic Microsystems for Biomedical Applications

In recent years, there has been a growing interest in the removal of blood-borne toxins through the use of magnetic nanocomposites. These toxins circulate in the bloodstream and can have a detrimental impact on health. Blood detoxification using magnetic beads comprised of an extracorporeal process where the patientâ??s blood is mixed with the magnetic materials with the ultimate goal of selectively removing the toxin while maintaining normal functionality of blood constituents. Once the adsorption of the toxins by the beads surface is completed, the magnetic separation stage takes place and the toxins are removed along with the material, leading to a toxin-free blood solution that returns to the circulatory system of the patient. Selective sequestration of these toxins from the patientâ??s blood using functionalized magnetic particles can improve the effectiveness of treatment while reducing side effects compared to conventional methods [1]. The aim of this work is to contribute to the design of continuous-flow magnetic separators and discuss their application for the recovery of magnetic beads from flowing blood streams.

Numerous microfluidic magnetic separator designs have been proposed in the last few years to recover magnetic beads from fluids; however, the application of continuous-flow systems offers numerous advantages such as higher separation efficacy and greater throughput as compared to batch separators. When using continuous microdevices, the magnetic beads and the adsorbed toxin are continuously injected through one inlet, deflected from the original blood stream and collected into a flowing buffer stream by a magnetic gradient applied perpendicular to the flow direction. In order to employ this separator, two fundamental requirements must be met, i.e. the complete recovery of the magnetic beads from the blood solution and the minimization of intermixing between the blood and buffer streams inside the device.

With regard to the evaluation of using continuous-flow systems for this application, we introduce a combination of magnetic and fluidic computational modelling that describes the bead trajectory inside a continuous microchannel under the influence of an external magnetic field (due to a permanent magnet) and the potential mixing between fluid streams. The model reported here represents a rational design guide for experimentalists in this field of research since it can be used to predict the separator efficacy taking into account key operating variables and impact parameters, such as bead and fluid properties, the characteristics of the magnets employed, the dimension of the microchannel and the selected flow rates.

Additionally, the experimental performance of a microfluidic magnetic separator was evaluated. Aqueous solutions of fluorescein and magnetic particles functionalized with fluorophores have been used in order to quantify both the mixing of both fluids inside the device and the particle separation efficacy according to the analysis of the images taken using an epi-fluorescent microscope. The theoretical and experimental results are compared and discussed.

Finally, it should be noted that although the fundamentals of continuous-flow magnetic separators have been previously discussed in the literature [2,3], a key distinguishing feature of this research is that we study, for the first time, the interaction between two fluids flowing simultaneously in the device while taking into account the effects of particle-fluid interactions in the flow field and potential diffusion between both streams.

ACKNOWLEDGEMENTS

Financial support from the Spanish Ministry of Economy and Competitiveness under the project CTQ2015-66078 is gratefully acknowledged. Jenifer Gómez-Pastora also thanks the FPI postgraduate research grant (BES-2013-064415).

REFERENCES:

1. â??Magnetic separation-based blood purification: A promising new approach for the removal of disease-causing compounds?â?, I.K. Herrmann, A.A Schlegel, R. Graf, W.J. Stark, and B. Beck-Schimmer, J. Nanobiotechnology 2015, 13(1), 49â??52.
2. â??Magnetic biotransport: analysis and applicationsâ?, E.P. Furlani, Materials 2010, 3, 2412â??2446.
3. â??Scalability analysis of magnetic bead separation in a microchannel with an array of soft magnetic elements in a uniform magnetic fieldâ?, S.A. Khashan, E.P. Furlani, Sep. Purif. Technol. 2014, 125, 311â??318.