Education & Certifications


  • M.S, Stanford University, Aeronautics and Astronautics (2014)
  • B.S, University of Michigan, Aerospace Engineering (2012)

Stanford Advisors


Current Research and Scholarly Interests


My research interests focus on droplet-based microfluidics and related complex fluid problems.

Lab Affiliations


All Publications


  • Microfluidic guillotine for single-cell wound repair studies. Proceedings of the National Academy of Sciences of the United States of America Blauch, L. R., Gai, Y., Khor, J. W., Sood, P., Marshall, W. F., Tang, S. K. 2017; 114 (28): 7283–88

    Abstract

    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.

    View details for DOI 10.1073/pnas.1705059114

    View details for PubMedID 28652371

    View details for PubMedCentralID PMC5514750

  • Amphiphilic nanoparticles suppress droplet break-up in a concentrated emulsion flowing through a narrow constriction. Biomicrofluidics Gai, Y., Kim, M., Pan, M., Tang, S. K. 2017; 11 (3): 034117

    Abstract

    This paper describes the break-up behavior of a concentrated emulsion comprising drops stabilized by amphiphilic silica nanoparticles flowing in a tapered microchannel. Such geometry is often used in serial droplet interrogation and sorting processes in droplet microfluidics applications. When exposed to high viscous stresses, drops can undergo break-up and compromise their physical integrity. As these drops are used as micro-reactors, such compromise leads to a loss in the accuracy of droplet-based assays. Here, we show droplet break-up is suppressed by replacing the fluoro-surfactant similar to the one commonly used in current droplet microfluidics applications with amphiphilic nanoparticles as droplet stabilizer. We identify parameters that influence the break-up of these drops and demonstrate that break-up probability increases with increasing capillary number and confinement, decreasing nanoparticle size, and is insensitive to viscosity ratio within the range tested. Practically, our results reveal two key advantages of nanoparticles with direct applications to droplet microfluidics. First, replacing surfactants with nanoparticles suppresses break-up and increases the throughput of the serial interrogation process to 3 times higher than that in surfactant system under similar flow conditions. Second, the insensitivity of break-up to droplet viscosity makes it possible to process samples having different composition and viscosities without having to change the channel and droplet geometry in order to maintain the same degree of break-up and corresponding assay accuracy.

    View details for DOI 10.1063/1.4985158

    View details for PubMedID 28652887

    View details for PubMedCentralID PMC5466449

  • Internal flow in droplets within a concentrated emulsion flowing in a microchannel PHYSICS OF FLUIDS Leong, C. M., Gai, Y., Tang, S. K. 2016; 28 (11)

    View details for DOI 10.1063/1.4968526

    View details for Web of Science ID 000390237300004

  • Spatiotemporal periodicity of dislocation dynamics in a two-dimensional microfluidic crystal flowing in a tapered channel. Proceedings of the National Academy of Sciences of the United States of America Gai, Y., Leong, C. M., Cai, W., Tang, S. K. 2016; 113 (43): 12082-12087

    Abstract

    When a many-body system is driven away from equilibrium, order can spontaneously emerge in places where disorder might be expected. Here we report an unexpected order in the flow of a concentrated emulsion in a tapered microfluidic channel. The velocity profiles of individual drops in the emulsion show periodic patterns in both space and time. Such periodic patterns appear surprising from both a fluid and a solid mechanics point of view. In particular, when the emulsion is considered as a soft crystal under extrusion, a disordered scenario might be expected based on the stochastic nature of dislocation dynamics in microscopic crystals. However, an orchestrated sequence of dislocation nucleation and migration is observed to give rise to a highly ordered deformation mode. This discovery suggests that nanocrystals can be made to deform more controllably than previously thought. It can also lead to novel flow control and mixing strategies in droplet microfluidics.

    View details for PubMedID 27790994

    View details for PubMedCentralID PMC5087054

  • Confinement and viscosity ratio effect on droplet break-up in a concentrated emulsion flowing through a narrow constriction. Lab on a chip Gai, Y., Khor, J. W., Tang, S. K. 2016; 16 (16): 3058-3064

    Abstract

    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.

    View details for DOI 10.1039/c6lc00478d

    View details for PubMedID 27194099

  • Optofluidic ultrahigh-throughput detection of fluorescent drops. Lab on a chip Kim, M., Pan, M., Gai, Y., Pang, S., Han, C., Yang, C., Tang, S. K. 2015; 15 (6): 1417-1423

    View details for DOI 10.1039/c4lc01465k

    View details for PubMedID 25588522