A numerical design study of chaotic mixing of magnetic particles in a microfluidic bio-separator

Abstract

A two-dimensional numerical investigation into the mixing of magnetic microparticles with bio-cells in a chaotic micromixer is carried out by using a multiphysics finite element analysis package. Fluid and magnetic problems are simulated in steady-state and time-dependent modes, respectively. Intensity of segregation is utilized as the main index to examine the efficiency of the mixer. Trajectories of the particles are used in order to detect chaos in their motion and quantify its extent. Moreover, probability of the collision between particles and target bio-cells is examined as a supplemental index to study the effects of driving parameters on the mixing process. Simulation results reveal that while in some ranges of operating conditions all indices are in good agreement, there are some ranges where they appear to predict contradicting results which is discussed in details. It is found that optimum operating conditions for the system is obtained when the Strouhal number is less than 0.6, which corresponds to the efficiency of about 85% in a mixing length of 500 lm (The mixer design described here is patent pending).

Effects of Magnetic Particles Entrance Arrangements on Mixing Efficiency of a Magnetic Bead Micromixer

“…At limit, when the particle's volume fraction of dispersed phase is very small, particles are treated as "points". It is a very usual method that is used by many researchers such as [4,5,7]. In this situation particle's volume is assumed to be zero, therefore there is no angular velocity and the only equation that should be solved is the linear momentum equation.…”

“…In micro scale devices where the Reynolds number is often less than 1, mixing is not a trivial task due to the absence of turbulence. In such circumstances, mixing relies merely on molecular diffusion which is a very slow phenomenon [4]. To resolve this problem many researchers have proposed several different kinds of micromixers with various techniques for improving mixing.…”

“…One group of magnetic bead micromixer is designed to mix magnetic micro beads with a bio-fluidic solution to collect target cells or biomolecules (e.g. DNA, RNA and protein) by means of the special cover of the beads [4,8,11,12]. This active micromixer has some advantages over passive micromixer in magnetic bio-particle separation.…”

“…This active micromixer has some advantages over passive micromixer in magnetic bio-particle separation. For example by using lamination for mixing of particle laden fluids in a passive micromixer, clogging the narrow channels is quite probable [4].…”

“…Suzuki et al [8,12] presented a magnetic bead micromixer as a bio-particle separator and performed some numerical investigation based on one-way coupling assumption between particles and fluid by using the superposition numerical method. Zolgharni et al [4] proposed a magnetic bead micromixer which was similar to Suzuki's micromixer basically. They performed a 2D study on that by using the superposition numerical method based on one-way coupling assumption between particles and fluid flow and find the optimum range of micromixer function according to some important micromixer's properties.…”