Fig. 3. Examples of droplet manipulation.
We divide droplet manipulation techniques into four categories that are typically used in droplet systems and are important for downstream applications. a, Droplet generation. Left: a schematic of acoustophoretic printing in which droplet generation is controlled by balancing the capillary force, gravity, acoustic force and radiation pressure. Right: a large-area image made from droplets produced by rasterized acoustophoretic printing. b, Droplet transportation and sorting. The use of magnetic beads to transport (orange), split (green), release (blue) and rotate (yellow) 250-μl droplets. The images show the state of the system at different times, t, into the process. The grey arrows indicate the direction that the robots are travelling in. c, Droplet splitting. The schematic for parallel plate droplet splitting. Droplets containing cells are first spotted onto a glass plate and allowed to incubate. Samples of the cell culture supernatants are extracted by applying a separate plate from above to which the droplets adhere, which is then removed to split the droplets while the cells remain in the droplets on the bottom plate owing to the effect of gravity. d, Droplet extraction. Images (top) and schematics (bottom) of the extraction of a single droplet using pipette aspiration. Part a is adapted from ref. 25, AAAS. Part b is reprinted with permission from ref. 35, AAAS. Part c is adapted with permission from ref. 20, American Chemical Society. Part d is adapted with permission from ref. 64, PNAS.