Continuous separation of microparticles in a microfluidic channel via the elasto-inertial effect of non-Newtonian fluid

Abstract

Pure separation and sorting of microparticles from complex fluids are essential for biochemical analyses and clinical diagnostics. However, conventional techniques require highly complex and expensive labeling processes for high purity separation. In this study, we present a simple and label-free method for separating microparticles with high purity using the elasto-inertial characteristic of a non-Newtonian fluid in microchannel flow. At the inlet, particle-containing sample flow was pushed toward the side walls by introducing sheath fluid from the center inlet. Particles of 1 μm and 5 μm in diameter, which were suspended in viscoelastic fluid, were successfully separated in the outlet channels: larger particles were notably focused on the centerline of the channel at the outlet, while smaller particles continued flowing along the side walls with minimal lateral migration towards the centerline. The same technique was further applied to separate platelets from diluted whole blood. Through cytometric analysis, we obtained a purity of collected platelets of close to 99.9%. Conclusively, our microparticle separation technique using elasto-inertial forces in non-Newtonian fluid is an effective method for separating and collecting microparticles on the basis of size differences with high purity.

Dynamics of particle migration in channel flow of viscoelastic fluids

“…the particle may move towards or away from the channel centreline depending on its initial position. The same behaviour is also observed in experiments (Nam et al 2012). The second normal stress difference leads to a secondary flow in a non-circular channel, which may also directly affect the particle motion by advection (Villone et al 2013).…”

“…The migration velocity of the particle is the most important measure of particle focusing, and its dependence on the particle size has been used for particle separation applications (Nam et al 2012;Kang et al 2014;Lim et al 2014b). In figures 5 (a) and (b), we plot the particle migration velocity V p as a function of particle position Y p in Oldroyd-B and Giesekus fluids, respectively.…”

Size-Based Separation of Particles and Cells Utilizing Viscoelastic Effects in Straight Microchannels

“…Still, the operating flow rate is one order magnitude higher than existing viscoelasticity-based separation. 35,42,55 Though the present throughput (3×10 8 cells/h at 3 ml/h with 1% hematocrit) is an order of magnitude lower than that of typical inertial microfluidic devices (≥10 9 cells/h), good parallelizability of straight geometry can offset the relatively low throughput of a single channel. Several groups have demonstrated the feasibility of parallelization of tens 29 or even hundreds 65 of channels for the high throughput.…”

“…In contrast to the 15 µm particles, 5 µm particles (κ = 0.1) were focused along the centerline as observed in previous works. 27,35,36,40,42,48,57 A large particle tends to migrate towards the wall when it displaces from the channel center. The major portion of fluid chooses to flow through the larger gap between the particle and the channel wall.…”

“…The off-center focusing has only been reported by numerical studies (κ ≥ 0.25) and macroscale experiments (κ = 0.6). 54,56 Most existing studies manipulate particles or cells with κ around 0.1 in square microchannels, 27,35,36,42,48,57,[59][60][61] and thus this off-center focusing was not discovered in these experiments. This off-center focusing is quite different from that in inertial flow Page 6 of 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 of Newtonian fluids.…”