Interfacial tension driven open droplet microfluidics.

Droplet microfluidics enables compartmentalized reactions in small scales and has been utilized for a variety of applications across chemical analysis, material science, and biology. While droplet microfluidics is a successful technology, barriers include high "activation energy" to develop custom applications and complex peripheral equipment. These barriers limit the adoption of droplet microfluidics in labs or prototyping environments. We demonstrate for the first time an open channel droplet microfluidic system that autonomously generates droplets at low Capillary numbers. Hundreds of droplets are produced in a run using only an open channel, pipettes, and a commercially available carrier fluid. Conceptual applications that showcase the process of droplet generation, splitting, transport, incubation, mixing, and sorting are demonstrated. The open nature of the device enables the use of physical tools such as tweezers and styli to directly access the system; with this, a new method of droplet sorting and transfer unique to open systems is demonstrated. This platform offers enhanced usability, direct access to the droplet contents, easy manufacturability, compact footprint, and high customizability. This design is a first step in exploring the space of power-free open droplet microfluidic systems and provides design rules for similar channel designs.