Continuous particle separation in spiral microchannels using dean flows and differential migration

Abstract

Microparticle separation and concentration based on size has become indispensable in many biomedical and environmental applications. In this paper we describe a passive microfluidic device with spiral microchannel geometry for complete separation of particles. The design takes advantage of the inertial lift and viscous drag forces acting on particles of various sizes to achieve differential migration, and hence separation, of microparticles. The dominant inertial forces and the Dean rotation force due to the spiral microchannel geometry cause the larger particles to occupy a single equilibrium position near the inner microchannel wall. The smaller particles migrate to the outer half of the channel under the influence of Dean forces resulting in the formation of two distinct particle streams which are collected in two separate outputs. This is the first demonstration that takes advantage of the dual role of Dean forces for focusing larger particles in a single equilibrium position and transposing the smaller particles from the inner half to the outer half of the microchannel cross-section. The 5-loop spiral microchannel 100 microm wide and 50 microm high was used to successfully demonstrate a complete separation of 7.32 microm and 1.9 microm particles at Dean number De = 0.47. Analytical analysis supporting the experiments and models is also presented. The simple planar structure of the separator offers simple fabrication and makes it ideal for integration with on-chip microfluidic systems, such as micro total analysis systems (muTAS) or lab-on-a-chip (LOC) for continuous filtration and separation applications.

Particle Focusing in Curved Microfluidic Channels

“…Several of these empirical studies have been completed about curved inertial focusing channels investigating different curve designs 21,26 , scalability 28,29 and dynamics of the focusing behavior 9,25 . The majority of these studies incorporated some method of varying the balance of inertial lift and Dean drag forces, most often accomplished by changing flow rate 19,23,24,27,28,30,31 but also by changing the cross section 24,22,25 , and investigating multiple lanes of a spiral with different curvature values 9,25 . However, every one of these previous studies have varied both important non-dimensional parameters (Re C and De) simultaneously or measured the particle behavior for different residence times at a given flow rate, which has been shown to affect eventual focusing behavior 25 .…”

Dean flow focusing and separation of small microspheres within a narrow size range

“…Firstly, in terms of its ability to concentrate and separate to individual fluid output ports, small, closely sized 2.1 and 3.2 lm microspheres. These microspheres are approximately five times smaller in diameter than the most closely ratiometrically spaced microparticle sizes previously reported as separated by Dean flow (10, 15 and 20 lm) (Kuntaegowdanahalli et al 2009) and significantly more closely ratiometrically spaced by size than the smallest separated particle sizes previously reported (1.9 and 7.32 lm) (Bhagat et al 2008a). Secondly, we examine its ability to clean-up and direct to an individual output port, 1.0 lm microspheres simulating assay target materials cleaned from 2.1 to 3.2 lm microspheres that represent contamination in the context of the 1.0 lm microspheres output port.…”

“…Dean flow, inertial focusing of spherical microparticles with diameters ranging between 5 and 20 lm has demonstrated the promise of efficient separation as well as increased throughput (Russom et al 2009;Kuntaegowdanahalli et al 2009;Xiang et al 2012;Bhagat et al 2008a). High throughput separation of 10 lm microparticles has also been performed using the Dean flow effect within 'U'-and 'S'-shaped channels (Ardabili et al 2010).…”

Lateral migration of dual droplet trains in a double spiral microchannel

“…Moreover, introduction of asymmetrical channel structure can also produce lift forces in simple systems [20]. Curved structures like serpentine or spiral have been frequently employed to improve the performance of inertial manipulation of rigid particles [16,35,36]. For droplets in low Re flows, curved channels would also influence the migration behaviour, which is rarely addressed in existing studies.…”