K-Channel: A Multifunctional Architecture for Dynamically Reconfigurable Sample Processing in Droplet Microfluidics

Abstract

By rapidly creating libraries of thousands of unique, miniaturized reactors, droplet microfluidics provides a powerful method for automating high-throughput chemical analysis. In order to engineer in-droplet assays, microfluidic devices must add reagents into droplets, remove fluid from droplets, and perform other necessary operations, each typically provided by a unique, specialized geometry. Unfortunately, modifying device performance or changing operations usually requires re-engineering the device among these specialized geometries, a time-consuming and costly process when optimizing in-droplet assays. To address this challenge in implementing droplet chemistry, we have developed the “K-channel,” which couples a cross-channel flow to the segmented droplet flow to enable a range of operations on passing droplets. K-channels perform reagent injection (0–100% of droplet volume), fluid extraction (0–50% of droplet volume), and droplet splitting (1:1–1:5 daughter droplet ratio). Instead of modifying device dimensions or channel configuration, adjusting external conditions, such as applied pressure and electric field, selects the K-channel process and tunes its magnitude. Finally, interfacing a device-embedded magnet allows selective capture of 96% of droplet-encapsulated superparamagnetic beads during 1:1 droplet splitting events at ~400 Hz. Addition of a second K-channel for injection (after the droplet splitting K-channel) enables integrated washing of magnetic beads within rapidly-moving droplets. Ultimately, the K-channel provides an exciting opportunity to perform many useful droplet operations across a range of magnitudes without requiring architectural modifications. Therefore, we envision the K-channel as a versatile, easy to use microfluidic component enabling diverse, in-droplet (bio)chemical manipulations.

Microfluidics for Biosynthesizing: from Droplets and Vesicles to Artificial Cells

“…Furthermore, based on the principles of mechanical [129][130][131][132][133][134][135] or thermal [136] forces, the manipulation of droplets based on mechanical and thermal forces can also be achieved by designing the structures of the microfluidic chip.…”

Opto-acousto-fluidic microscopy for three-dimensional label-free detection of droplets and cells in microchannels

“…due to its highthroughput compartmentalization of nano or picoliter-sized environments for biochemical assays 1, 2 . To date, droplet manipulation techniques have been intensively investigated and developed, such as control of droplet size 3 , coalescence of droplet 4 , droplet splitting 5 , injection of droplet 6 and etc.…”

Droplet microfluidics in thermoplastics: device fabrication, droplet generation, and content manipulation using integrated electric and magnetic fields

“…1–4 Accordingly, droplets have found utility in a variety of integrated (bio)chemical analyses such as single-cell protein profiling, 5 genome sequencing, 6 chromatin digestion and nucleosome positioning determination, 7 enzyme-modulator screening, 8, 9 protease activity determination, 10 and polymerase chain reaction of single-copy DNA molecules. 11 Droplets are primarily generated using T-junction 12 and flow-focusing configurations, 13 and integrated downstream operations have been developed to add reagents, 14, 15 incubate reactions, 16 merge and split droplets, 15, 17, 18 or use electric and magnetic fields to sort droplets of interest. 19–21…”

“…Beyond droplet generation, 12, 13 the range of useful droplet manipulations includes direct reagent injection into droplets 14, 15 and droplet splitting to parallelize reactions or remove waste, 15, 43, 44 among others, 1 providing needed control over in-droplet chemistry. While these operations have been well characterized in PDMS, translation of droplet technologies into thermoplastics for mass fabrication depends on robustly demonstrating these processes in thermoplastic devices.…”

“…44, 45 More recently, we developed a multifunctional K-channel geometry for manipulating droplets and leveraged it for not only direct injections but also for selective droplet decanting and washing steps via integrated magnetic field that concentrated in-droplet magnetic beads during droplet splitting operations. 15 To realize these components in thermoplastics, it is critical to establish material compatibility with required electric and magnetic fields as well as to fundamentally replicate channel features with spatial resolution and fidelity comparable to PDMS. Ideally, droplet microfluidic device components would be tested both individually and as integrated devices to broadly demonstrate the applicability of thermoplastic materials for sophisticated droplet microfluidic analyses.…”