Continuous Inertial Focusing and Separation of Particles by Shape

Abstract

An effective approach to separating shaped particles is needed to isolate disease-causing cells for diagnostics or to aid in purifying nonspherical particles in applications ranging from food science to drug delivery. However, the separation of shaped particles is generally challenging, since nonspherical particles can freely rotate and present different faces while being sorted. We experimentally and numerically show that inertial fluid-dynamic effects allow for shape-dependent separation of flowing particles. (Spheres and rods with aspect ratios of $3:1$ and $5:1$ have all been separable.) Particle rotation around a conserved axis following Jeffery orbits is found to be a necessary component in producing different equilibrium positions across the channel that depend on particle rotational diameter. These differences are large enough to enable passive, continuous, high-purity, high-throughput, and shape-based separation downstream. Furthermore, we show that this shape-based separation can be applied to a large range of particle sizes and types, including small, artificially made $3\mathrm{\text{−}}\mu \mathrm{m}$ particles as well as bioparticles such as yeast. This practical approach for sorting particles by a previously inaccessible geometric parameter opens up a new capability that should find use in a range of fields.

• Received 20 March 2012

DOI: https://doi.org/10.1103/PhysRevX.2.031017

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Authors & Affiliations

Mahdokht Masaeli^1,2,*, Elodie Sollier^1,2,†, Hamed Amini^1,2, Wenbin Mao³, Kathryn Camacho⁴, Nishit Doshi⁴, Samir Mitragotri⁴, Alexander Alexeev³, and Dino Di Carlo^1,2,‡

• ¹Department of Bioengineering, University of California, Los Angeles, 410 Westwood Plaza, Los Angeles 90095, California, USA
• ²California NanoSystems Institute, University of California, Los Angeles 90095, California, USA
• ³Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 771 Ferst Drive Northwest, Atlanta 30332, Georgia, USA
• ⁴Department of Chemical Engineering, University of California, Santa Barbara,, Mail Code 5080, Santa Barbara 93106, California, USA

• ^*Corresponding author. mahdokhtm@ucla.edu
• ^†Corresponding author. esollier@ucla.edu
• ^‡Corresponding author. dicarlo@seas.ucla.edu

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Popular Summary

Separation of both natural and manmade particles from a background of other particles is essential in a variety of applications: It helps researchers isolate cells that cause disease and allows collection of particles with specific geometric properties in industrial processes. Filter separation using barriers with selected pore sizes is not effective for nonspherical particles, however, since they present different faces while passing through the openings. In our paper, we show with experiments and numerical simulations that inertial effects of a fluid flowing in a channel offer a way to achieve shape-dependent separation of particles with a variety of sizes and shapes.

When microparticles are placed in a channel containing moving liquid, the momentum of the fluid causes the particles to rotate and migrate across stream lines as they move along the channel. In this situation, rotating particles of different shapes eventually occupy different stable positions in the channel cross section. Rod-like particles stay closer to the center of the channel, while spherical particles tend to stay near the walls. These focusing effects are large enough to enable high-purity shape-based separation of large quantities of particles into separate outlets.

We have applied this technique to a large range of particle sizes and types, including spherical and ellipsoidal particles as small as 3 microns as well as biological particles such as budding yeast with different shapes during the cell life cycle. Our calculations predict stable focusing positions that depend on the particle's largest cross-sectional dimension, and this prediction is confirmed by our imaging studies. This simple and practical approach for sorting particles opens up a new capability that should find use in a range of fields from preparing standardized anisotropic particles for composite materials to synchronizing the life cycles of yeast and bacteria populations for controlled experiments.

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References

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Source: https://link.aps.org/doi/10.1103/PhysRevX.2.031017

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