Wound repair is a key feature distinguishing living from nonliving matter. Single cells are increasingly recognized to be capable of healing wounds. The lack of reproducible, high-throughput wounding methods has hindered single-cell wound repair studies. This work describes a microfluidic guillotine for bisecting single Stentor coeruleus cells in a continuous-flow manner. Stentor is used as a model due to its robust repair capacity and the ability to perform gene knockdown in a high-throughput manner. Local cutting dynamics reveals two regimes under which cells are bisected, one at low viscous stress where cells are cut with small membrane ruptures and high viability and one at high viscous stress where cells are cut with extended membrane ruptures and decreased viability. A cutting throughput up to 64 cells per minute-more than 200 times faster than current methods-is achieved. The method allows the generation of more than 100 cells in a synchronized stage of their repair process. This capacity, combined with high-throughput gene knockdown in Stentor, enables time-course mechanistic studies impossible with current wounding methods.
This paper describes the dimensionless groups that determine the break-up probability of droplets in a concentrated emulsion during its flow in a tapered microchannel consisting of a narrow constriction. Such channel geometry is commonly used in droplet microfluidics to investigate the content of droplets from a concentrated emulsion. In contrast to solid wells in multi-well plates, drops are metastable, and are prone to break-up which compromises the accuracy and the throughput of the assay. Unlike single drops, the break-up process in a concentrated emulsion is stochastic. Analysis of the behavior of a large number of drops (N > 5000) shows that the probability of break-up increases with applied flow rate, the size of the drops relative to the size of the constriction, and the viscosity ratio of the emulsion. This paper shows that the break-up probability collapses into a single curve when plotted as a function of the product of capillary number, viscosity ratio, and confinement factor defined as the un-deformed radius of the drop relative to the hydraulic radius of the constriction. Fundamentally, the results represent a critical step towards the understanding of the physics governing instability in concentrated emulsions. Practically, the results provide a direct guide for the rational design of microchannels and the choice of operation parameters to increase the throughput of the droplet interrogation step while preserving droplet integrity and assay accuracy.
droplet generating system, the top side of the channel is exposed to air, rather than being enclosed by a ceiling, which gives access to the channel where conventional droplet microfluidics with enclosed channels does not. Open channels are advantageous because a researcher can directly pipette into the channel or add/retrieve droplets, solid objects such as magnetic beads, or tissue samples as they wish. We demonstrate downstream manipulations such as sorting, splitting, and mixing that are uniquely enabled by the open nature of the system and the ability to access droplets with simple tools such as styli, tweezers, and a needle. The ability to move and manipulate droplets with simple tools through the open surface allows our method to be used in chemistry and biology labs without microfluidics experience and allows faster prototypingthat is, it is easy to add in new processing steps or workflows that require droplets to be relocated to a different space on-or off chip. Prior methods for moving droplets within microfluidic devices such as electrowetting on dielectric [1][2][3] optical tweezers, [4,5] and complex valving systems [6,7] require significant expertise; our system provides a "plug and play" approach for prototyping and executing new experimental workflows. This work has potential to open new avenues in droplet microfluidics, a field which has grown immensely in the past decade. [8][9][10][11][12][13][14][15][16][17][18] Droplet microfluidics is an attractive technology because it miniaturizes and compartmentalizes chemical and biological processes, reduces reagent waste, and enables the use of precious or expensive reagents. The microliter to picoliter droplets act as chambers to conduct biological or chemical analyses and have many important applications in DNA sequencing, directed evolution, materials chemistry, and chemical reactions. [8][9][10][11][12][13][14][15][16][17][18] Additionally, droplet manipulations such as sorting, mixing, and splitting are empowering for expanding the versatility and potential applications of droplet microfluidics. [8,9,[12][13][14][15][16][17][18] Our open channel droplet generator presented here is distinct from prior work in that it shows autonomous generation of droplets from an open capillary flow without the direct actuation of a pipette to generate each droplet. In our system, we autonomously generate droplets in an open channel without pumps or tubing by leveraging spontaneous capillary flow (SCF -flow induced by capillary action), [19][20][21][22][23][24] capillary pressure, and the hydrostatic pressure difference between two immiscible fluids (the fluorinated carrier phase and aqueous phase). Previous work in open droplet microfluidics includes the analysis of different modes of immiscible fluid plug flow in anDroplet microfluidics enables compartmentalized reactions in small scales and is utilized for a variety of applications across chemical analysis, material science, and biology. While droplet microfluidics is a successful technology, barriers include h...
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