title: Synchronized reinjection and coalescence of droplets in microfluidics.
abstract: Coalescence 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.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA. vnm@seas.harvard.edu.
authors.forename: Manhee
authors.initials: M
authors.lastname: Lee
authors.forename: Jesse W
authors.initials: JW
authors.lastname: Collins
authors.forename: Donald M
authors.initials: DM
authors.lastname: Aubrecht
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Sperling
authors.forename: Laura
authors.initials: L
authors.lastname: Solomon
authors.forename: Jong-Wook
authors.initials: JW
authors.lastname: Ha
authors.forename: Gi-Ra
authors.initials: GR
authors.lastname: Yi
authors.forename: David A
authors.initials: DA
authors.lastname: Weitz
authors.forename: Vinothan N
authors.initials: VN
authors.lastname: Manoharan
mesh_terms: D006874:Hydrostatic Pressure; D044085:Microfluidics / Q000295:instrumentation / Q000379:methods*; D009821:Oils / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D009821:Oils; D013501:Surface-Active Agents; D014867:Water