Lee, ManheeCollins, Jesse KenasAubrecht, Donald MichaelSperling, Ralph A.Solomon, LauraHa, Jong-WookYi, Gi-RaWeitz, DavidManoharan, Vinothan2016-01-262014Lee, Manhee, Jesse W. Collins, Donald M. Aubrecht, Ralph A. Sperling, Laura Solomon, Jong-Wook Ha, Gi-Ra Yi, David A. Weitz, and Vinothan N. Manoharan. 2014. “Synchronized Reinjection and Coalescence of Droplets in Microfluidics.” Lab Chip 14 (3): 509–513. doi:10.1039/c3lc51214b.1473-0197http://nrs.harvard.edu/urn-3:HUL.InstRepos:24902771Coalescence of two kinds of pre-processed droplets is necessary to perform chemical and biological assays in droplet-based microfluidics. However, a robust technique to accomplish this does not exist. Here we present a microfluidic device to synchronize the reinjection of two different kinds of droplets and coalesce them, using hydrostatic pressure in conjunction with a conventional syringe pump. We use a device consisting of two opposing T-junctions for reinjecting two kinds of droplets and control the flows of the droplets by applying gravity-driven hydrostatic pressure. The hydrostatic-pressure operation facilitates balancing the droplet reinjection rates and allows us to synchronize the reinjection. Furthermore, we present a simple but robust module to coalesce two droplets that sequentially come into the module, regardless of their arrival times. These re-injection and coalescence techniques might be used in lab-on-chip applications requiring droplets with controlled numbers of solid materials, which can be made by coalescing two pre-processed droplets that are formed and sorted in devices.en-USJournal Article2015-12-26Manhee Lee, Jesse W. Collins, Donald M. Aubrecht, Ralph A. Sperling, Laura Solomon, Jong-wook Ha, Gi-Ra Yi, David A. Weitz, and Vinothan N. Manoharan2016-01-2610.1039/c3lc51214b