Abstract
Droplet microfluidics offers a wide range of applications, including high-throughput drug screening and single-cell DNA amplification. However, these platforms are often limited to single-input conditions that prevent them from analyzing multiple input parameters (e.g., combined cellular treatments) in a single experiment. Droplet multiplexing will result in higher overall throughput, lowering cost of fabrication, and cutting down the hands-on time in number of applications such as single-cell analysis. Additionally, while lab-on-a-chip fabrication costs have decreased in recent years, the syringe pumps required for generating droplets of uniform shape and size remain cost-prohibitive for researchers interested in utilizing droplet microfluidics. This work investigates the potential of simultaneously generating droplets from a series of three in-line T-junctions utilizing gravity-driven flow to produce consistent, well-defined droplets. Implementing reservoirs with equal heights produced inconsistent flow rates that increased as a function of the distance between the aqueous inlets and the oil inlet. Optimizing the three reservoir heights identified that taller reservoirs were needed for aqueous inlets closer to the oil inlet. Studying the relationship between the ratio of oil-to-water flow rates (Φ) found that increasing Φ resulted in smaller droplets and an enhanced droplet generation rate. An ANOVA was performed on droplet diameter to confirm no significant difference in droplet size from the three different aqueous inlets. The work described here offers an alternative approach to multiplexed droplet microfluidic devices allowing for the high-throughput interrogation of three sample conditions in a single device. It also has provided an alternative method to induce droplet formation that does not require multiple syringe pumps.
Highlights
Droplet microfluidic devices have been demonstrated for a broad range of applications including nanoparticle synthesis [1,2], chemical reactions [3], protein crystallization [4], biological assays, and cellular analysis [5,6,7,8]
The commonly used flow-focusing generators can deliver monodisperse droplets at low capillary numbers (Ca) when droplets are produced in a highly stable breakup process [11]; a complex velocity field and several key parameters defining the geometry have made it challenging to model flow-focusing geometries analytically [12]
Theflow fluid flowfrom rates from each inlet werebased tunedonbased on a developed model that accurately predicted the relationship betweenbetween reservoirreservoir height and aqueous empirical model that accurately predicted the relationship height and flow rate
Summary
Droplet microfluidic devices have been demonstrated for a broad range of applications including nanoparticle synthesis [1,2], chemical reactions [3], protein crystallization [4], biological assays, and cellular analysis [5,6,7,8]. Uniform droplets are desired to ensure constant, controlled, and predictable outcomes. Some applications require a wide range of tunable droplet volumes, typically femtoliters to nanolitres. It is critical to have a deep and systematic understanding of microfluidic droplet formation. Microfluidic droplet production has been primarily achieved through T-junctions [9] or flow-focusing junctions [10]. The commonly used flow-focusing generators can deliver monodisperse droplets at low capillary numbers (Ca) when droplets are produced in a highly stable breakup process (e.g., dripping regime) [11]; a complex velocity field and several key parameters defining the geometry (e.g., oil and water channel width and height) have made it challenging to model flow-focusing geometries analytically [12]
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