Diamagnetic droplet microfluidics applied to single-cell sorting

Abstract

The heterogeneity of diseased tissue causes major challenges in the detection and treatment of disease. Such challenges have motivated the development of tools for single-cell isolation and analysis. However, many cell isolation methods in microfluidics rely on the use of cell-labeling steps or expose cells to potentially harmful forces. Here, we present a microfluidic method for label-free control of cell-encapsulating biocompatible droplets using negative magnetophoresis. Our system is distinguished from previous microfluidic diamagnetic sorting approaches by the encapsulation of the cells inside droplets, which isolates the cells from the magnetic continuous phase. The droplet phase is comprised of cells suspended in their growth culture medium, and all of the magnetic content is contained in the oil-based continuous phase. At a flow-focusing junction, empty droplets and cell-encapsulating droplets are both generated and surrounded by the magnetic continuous phase. Cell encapsulation produces a size distinction between empty droplets and cell-encapsulated droplets. Through the application of a permanent magnet to the system, diamagnetic size-based sorting of empty droplets from cell-encapsulated droplets is achieved with a purity of ∼84% in a single pass. Additionally, since the encapsulated cells are completely isolated from the magnetic content in the continuous phase, 88% cell-viability is observed after a two-hour incubation period. If combined with a single-cell assay, this system can provide label-free isolation of viable cells at a high purity for subsequent downstream analysis.

Cell Separations and Sorting

“…Buryk-Iggers et al 123 demonstrated a diamagnetic droplet microfluidic method in which cell-encapsulating droplets were precisely controlled based on magnetophoresis, a phenomenon where particles migrate in a magnetic field. The droplet phase was comprised of cells suspended in culture medium, and the magnetic content was contained in the continuous phase.…”

Cell Culture in Microfluidic Droplets

“…The application of a magnetic field on droplets rendered diamagnetic by the addition of ferromagnetic fluids (e.g., loaded with paramagnetic beads) can be used to place them into specific areas on chips . As an example, this method has been applied to separate empty droplets from cell-containing drops. , Other protocols have used acoustophoresis for droplet sorting, where piezoelectric transducers produce acoustic waves that can generate a pressure capable to modify the direction of the droplet movement in a flow . This method was applied for isolating cancer cells (HeLa) or for separating live and fixed cells from a mixed population (MCF-7). , …”

Numerical Investigation of Double Emulsion Droplets using Modified Flow Focusing Microfluidic Device for Drug Delivery

“…Microfluidics is able to control fluid flow precisely in the microchannel that usually presents in multiphase flow [1]. This technology has been successfully implemented in several fields as follows: lab on a chip [2], drug delivery [3], bio-medical [4], digital polymerase chain reaction (ddPCR) procedure [5], cell sorting [6], food industry [7] and chemical [8]. Although microfluidics plays an essential role in many sectors, the current development of this technology focuses on drug delivery since the world has been impinged by the Covid-19 pandemic for the last two years.…”