Trapping a moving droplet train by bubble guidance in microfluidic networks

Abstract

Trapping a train of moving droplets into preset positions within a microfluidic device facilitates the longterm observation of biochemical reactions inside the droplets. In this paper, a new bubble-guided trapping method, which can remarkably improve the limited narrow two-phase flow rate range of uniform trapping, was proposed by taking advantage of the unique physical property that bubbles do not coalescence with two-phase fluids and the hydrodynamic characteristic of large flow resistance of bubbles. The flow behaviors of bubble-free and bubble-guided droplet trains were compared and analyzed under the same two-phase flow rates. The experimental results show that the droplets trapped by bubble-free guided trapping exhibit the four trapping modes of sequentially uniform trapping, nonuniform trapping induced by break-up and collision, and failed trapping due to squeezing through, and the droplets exhibit the desired uniform trapping in a relatively small two-phase flow rate range.Compared with bubble-free guided droplets, bubble-guided droplets also show four trapping modes.However, the two-phase flow rate range in which uniform trapping occurs is increased significantly and the uniformity of the trapped droplet array is improved. This investigation is beneficial to enhance the applicability of microfluidic chips for storing droplets in a passive way.

Multiple interactions between microfluidic droplets and on-chip pneumatic valves

“…In either case, the order of the droplets cannot be preserved, the emulsion may be subjected to stability issues, and the addition of reagents to each droplet after incubation requires nontrivial synchronisation (Kaminski and Garstecki (2017)). By contrast, when the assay can be limited to a few hundreds of droplets, the latter can be trapped and incubated on-chip in droplet arrays, which alleviates much of the aforementioned challenges (Amselem et al (2016); Sart et al (2017); Zhang et al (2018a)). Droplet arrays have been successfully used to assemble cells in spheroids (Sart et al (2017)).…”