The manipulation of reagents and samples for multiple purposes including reactions and analysis for biotechnology, nanotechnology, and chemistry applications requires reproducibility and simplicity to be useful in practice. As microfluidic devices transition from a research project in and of themselves to a platform utilized by scientists investigating problems in a wide variety of fields, the ability to reproducibly control fluid and flow profiles for predictable results becomes as important as the device itself. The two most common types of fluid flow generation are hydrodynamic or pressure driven flow and electroosmotic flow. Both have advantages and disadvantages. The chief advantage of electroosmotic flow is the plug like flow profile that prevents dispersion in downstream analysis. However, generating a linear electric field in a small channel is fraught with challenges including preventing bubbles formed at the electrode or gas in the solution from interfering with the application of a uniform electric field. To solve this problem a combination of pressure driven flow and electroosmotic flow has been harnessed.
