Tuning the Splitting Behavior of Droplet in a Bifurcating Channel through Wettability-Capillarity Interaction

Droplet Microfluidics for Current Cancer Research: From Single-Cell Analysis to 3D Cell Culture

Cancer is the second leading cause of death worldwide. Differences in drug resistance and treatment response caused by the heterogeneity of cancer cells are the primary reasons for poor cancer therapy outcomes in patients. In addition, current in vitro anticancer drug-screening methods rely on two-dimensional monolayer-cultured cancer cells, which cannot accurately predict drug behavior in vivo. Therefore, a powerful tool to study the heterogeneity of cancer cells and produce effective in vitro tumor models is warranted to leverage cancer research. Droplet microfluidics has become a powerful platform for the single-cell analysis of cancer cells and three-dimensional cell culture of in vitro tumor spheroids. In this review, we discuss the use of droplet microfluidics in cancer research. Droplet microfluidic technologies, including single- or double-emulsion droplet generation and passive- or active-droplet manipulation, are concisely discussed. Recent advances in droplet microfluidics for single-cell analysis of cancer cells, circulating tumor cells, and scaffold-free/based 3D cell culture of tumor spheroids have been systematically introduced. Finally, the challenges that must be overcome for the further application of droplet microfluidics in cancer research are discussed.

Computational and Analytical Investigation of Droplet Impingement and Spreading Dynamics around the Right Circular Cone

Numerical computations are performed to elucidate the water droplet impingement and spreading dynamics around a small right-angled circular cone suspended in the air. An axisymmetric model employing the volume of fluid approach describes the engrossing impact, spreading, and detachment behavior of droplets around the solid substrate. Influence of various dimensionless pertinent factors, like Weber number (We), contact angle (θ), Ohnesorge number (Oh), Bond number (Bo), and cone base-to-droplet diameter ratio (Dc/Do) on maximum deformation factor (β_f) is demonstrated thoroughly to understand droplets' hydrodynamic and morphological behavior. An increase in We shortens the droplet's interaction duration with the substrate for a particular value of θ, Oh, and D_c/D_o. Moreover, the interaction time reduces drastically with the increase of Oh when θ, We, and D_c/D_o remain constant. Moreover, correlations are developed for both free (We = 0) and forced (We ≠ 0) falling of the droplet to determine the deformation factor as a function of various relevant dimensionless parameters, which operates satisfactorily within 0.8% of the computational data. Lastly, the maximum deformation factor for the droplet is calculated analytically, and it demonstrates an extremely good matching with simulated data.

Numerical Investigation on the Symmetric Breakup of Bubble within a Heated Microfluidic Y-Junction

This study numerically investigated the symmetric breakup of bubble within a heated microfluidic Y-junction. The established three-dimensional model was verified with the results in the literature. Two crucial variables, Reynolds number (Re) and heat flux (q), were considered. Numerical results demonstrated that the bubble breakup was significantly affected by phase change under the heated environment. The “breakup with tunnel” and “breakup with obstruction” modes respectively occurred at the low and high q. The breakup rate in pinch-off stage was much larger than that in squeezing stage. As Re increased, the bubble broke more rapidly, and the critical neck thickness tended to decrease. The bubble annihilated the vortices existing in the divergence region and made the fluid flow more uniform. The heat transfer was enhanced more drastically as Re was decreased or q was increased, where the maximum Nusselt number under two-phase case was 6.53 times larger than single-phase case. The present study not only helps understanding of the physical mechanisms of bubble behaviors and heat transfer within microfluidic Y-junction, but also informs design of microfluidic devices.