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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2018)

Droplet microfluidics offers a unique liquid-handling capability for various applications, such as single cell analysis and sorting, chemical synthesis and development of biochemical assays, diagnostics, drug screening, DNA sequencing and directed evolution. Producing highly monodisperse pico-liter to nano-liter droplets enables quantitative control of solute concentration, while compartmentalizing samples into droplets provides a precise chemical and bio-chemical environment. Small volume and high concentration of encapsulated samples allows for rapid processing and analysis of the thousands to millions of cells that must be screened to find a heterogenous population of interest. Being able to effectively sort droplets is in high demand.

A limiting factor for active sorting of droplets is the real time sensing and control mechanism that they require. The control components of active systems lead to a complex and expensive sorting device. On the other hand, passive methods of droplet sorting which operate based on intrinsic properties of droplets, are especially important to reduce the complexity and cost. Many biological reactions that occur inside droplets can alter droplet properties, such as viscosity, interfacial tension and viscoelasticity. In this study we focus on non-Newtonian fluids which exhibit viscoelastic properties. A need to passively sort droplets based on intrinsic properties, in an inertial flow regime, is of an immense importance.

Viscoelastic solutions possess unique properties such as shear rate dependence viscosity, and relaxation time. We developed an integrated microfluidics platform to generate, incubate, and sort droplet based on viscoelastic properties on-chip.

One approach to achieve this is by tuning the timescale of flow compare to relaxation time of viscoelastic droplets, where we engineered our platform to pre-deformed droplet, and the droplet retains its deformed shape within the relaxation time. This results in a significant enhancement in viscoelastic-based droplet sorting.

Viscoelastic solutions possess unique properties such as shear rate dependence viscosity, and relaxation time, which is an inherent property of a viscoelastic solutions. In this work we have developed an integrated microfluidics platform to generate, incubate and sort viscoelastic droplets of interest without the need for active sensing components.

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    Cover page: High Throughput Passive Inertial Separation of Viscoelastic Droplets in Microchannels
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2015)
    Circulating tumor cells (CTCs) are important biomarkers for monitoring tumor dynamics and efficacy of cancer therapy. Several technologies have been demonstrated to isolate CTCs with high efficiency but achieve a low purity from a large background of blood cells. We have previously shown the ability to enrich CTCs with high purity from large volumes of blood through selective capture in microvortices using the Vortex Chip. The device consists of a narrow channel followed by a series of expansion regions called reservoirs. Fast flow in the narrow entry channel gives rise to inertial forces, which direct larger cells into trapping vortices in the reservoirs where they remain circulating in orbits. By studying the entry and stability of particles following entry into reservoirs, we discover that channel cross sectional area plays an important role in controlling the size of trapped particles, not just the orbital trajectories. Using these design modifications, we demonstrate a new device that is able to capture a wider size range of CTCs from clinical samples, uncovering further heterogeneity. This simple biophysical method opens doors for a range of downstream interventions, including genetic analysis, cell culture, and ultimately personalized cancer therapy.
      Cover page: High efficiency vortex trapping of circulating tumor cells.
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