Droplet Production of Biological non-Newtonian Fluids and Bioassay Applications in a Microfluidic Network
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Date
2020-08-31
Authors
Marcali, Merve
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Droplet-based microfluidics has been developed over the last two decades and presented
as a promising platform for biochemical assay. This promise relies on the system’s ability to
quantify the reagents accurately with high throughput. In addition, since each droplet act
as a micro-reactor, faster reaction time and reduced reagent consumption can be achieved.
Most of these biochemical assays require biological samples to be handled, which is nonNewtonian in nature. However, there is little information on droplet formation dynamics of
biological non-Newtonian fluids. Therefore, this thesis investigates the formation dynamics
of the droplet of red blood cells as a non-Newtonian fluid. Then, a bio-assay to quantify the
viruses in red blood cell solution is developed by using droplet based microfluidic system
to show the system’s sensitivity and precision.
The first part of the thesis focuses on the droplet formation of biological non-Newtonian
fluids in a T-junction generator under the squeezing regime. In this regime, droplet formation with Newtonian fluids depends on T-junction geometry; however, the formation
depends on the aspect ratio and width ratio of the channel, the flow rate ratio of fluids,
and the viscosity ratio of the phases in the presence of the shear-thinning biological nonNewtonian fluids such as red blood cells. In addition, we analyze the impact of the red
blood cell concentration on the formation cycle. In the first part, we presented the experimental data of the red blood cell droplet evolution through the analysis of high-speed
videos. During this analysis, we tracked several operational parameters such as droplet
volume, the spacing between droplets, generation frequency by varying the flow conditions
of fluids, and the geometrical designs of the T-junction. Our analysis reveals that unlike
other non-Newtonian fluids, where the fourth stage exists (stretching stage), the formation
cycle consists of only three stages: lag, filling and necking stages. Based on the detailed
analysis of each stage, a mathematical model is developed to predict the final volume of the
red blood cell droplets in the second part, which can be utilized in sensitive biochemical
assay applications for future studies.
In the second part, we analyzed the three stages of single cycle of the droplet formation
and developed a mathematical model that describes the performance of the T-junction
generators for biological non-Newtonian fluids (i.e., red blood cells - (RBCs)). The model
integrated with a detailed analysis of the geometrical shape of the droplet during the
formation process and combined with analysis of a force balance and a Laplace pressure
balance to define the penetration depth and the critical neck thickness of the droplet. This
analysis captures the influence of the governing dimensionless parameters (i.e., channel
width and height, flow rate ratios, and fluid viscosities). The performance of the model was
validated by comparing the operational parameters (droplet volume, the spacing between the droplets and the generation frequency) with the experimental data across the range of
these dimensionless parameters. The model matches well with the experimental results as
data falls within 20% of the predicted values of the droplet volume.
The third part of this study focuses on the development of the biochemical assay using
a droplet-based microfluidic system. This study presents Influenza A virus/virus-like particles (VLPs) quantification by running hemagglutination assay (HA Assay) in a dropletbased microfluidic system. VLPs are genetically engineered non-infectious particles, which
have proteins to mimic the original virus but lack of genetic material to infect host organisms. Therefore, VLPs are good candidates for vaccine production. To determine the final
dosage of VLPs in the vaccine, HA assay is done using 96-well plates. In this assay, diluted
particles mixed with the target RBCs and the aggregation takes 4 hours to finalize. Although this method is a common procedure, longer reaction time, cross-contamination and
human errors are the major drawbacks of this system. To eliminate these disadvantages, a
droplet-based HA assay was developed. In this study, it was shown that the reaction time
dropped to 4-10 seconds due to small diffusion length in droplets, the cross-contamination
was prevented due to the compartmentalization nature of droplets, and the aggregation
reaction was detected by the image analysis to eliminate human error.
Description
Keywords
Droplet microfluidics, non-Newtonian fluid, red blood cells, hydrodynamics, virus quantification, Influenza virus, Hemagglutination assay