# Increasing Fluid Viscosity Ensures Consistent Single-Cell Encapsulation

## TL;DR

Increasing fluid viscosity improves consistent single-cell isolation in microfluidic systems, reducing biases caused by cell variability.

## Contribution

A novel method using increased fluid viscosity to ensure uniform single-cell encapsulation in microfluidics.

## Key findings

- Increasing fluid viscosity to 40–50 cP reduces cell sedimentation and improves encapsulation consistency.
- High-viscosity fluid enables uniform cell isolation regardless of cell type or properties.
- This method outperforms traditional density-based approaches for single-cell isolation.

## Abstract

High-throughput single-cell analysis typically relies
on the isolation
of cells of interest in separate compartments for subsequent phenotypic
or genotypic characterization. Using microfluidics, this is achieved
by isolating individual cells in microdroplets or microwells. However,
due to cell-to-cell variability in size, shape, and density, the cell
capture efficiencies may vary significantly. This variability can
negatively impact the measurements and introduce undesirable artifacts
when trying to isolate and characterize heterogeneous cell populations.
In this study, we show that single-cell isolation biases in microfluidics
can be circumvented by increasing the viscosity of fluids in which
cells are dispersed. At a viscosity of 40–50 cP (cP), the cell
sedimentation is effectively reduced, resulting in a steady cell flow
inside the microfluidics chip and consistent encapsulation in water-in-oil
droplets over extended periods of time. This approach allows nearly
all cells in a sample to be isolated with the same efficiency, irrespective
of their type. Our results show that increased fluid viscosity, rather
than cell-adjusted density, provides a more reliable approach to mitigate
single-cell isolation biases.