Mother Nature has already developed an intricate and awesome system for moving biological fluids around inside of organisms. Exploiting the physics of these biological situations is inspiring for further research, so that physics and biomicrofluidics can one day (hopefully) expand beyond natural bounds.
In an article in the August 30, 2007 Physics of Fluids Khatavkar and friends (sounds better than et al, doesn't it?) propose a design for a micromixer inspired by the cilia of bacteria like E. coli The article presents an outline for this bio-inspired scheme. The cilia can sit unobtrusively in a microchannel andpowered by an electromagnetic fieldnicely stir up a heterogeneous mixture.
Also taking a nod from human biological process, Yoon and friends published this article in the 2007 SPIE Proceedings of Nanosensors, Microsensors, and Biosensors and Systems.The researchers discuss and build artificial cilia that measure flow rate, direction, and other flow properties at microscopic levels. Once they take these measurements, the researchers can change the geometry of the flow channel to better accommodate or dissipate unwanted flow patterns. The researchers note that the idea came from observing how cilia are used in the kidney to measure how fluids are flowing. If there is an electrochemical or other change in the flow, the cilia can then give feedback, and the body will regulate tubule diameter. All of this is crucial for proper kidney function.
Biomimicry, as this type of bio-inspired design is sometimes called, has a lot of room to expand. An interesting related website is the Biomimicry Database, an open-source tool sponsored by the Rocky Mountain Institute, a non-profit in Boulder, Colorado. The database touts itself as: "A tool to cross-pollinate biological knowledge across discipline boundaries." Browsing their database is sort of amazing, and there's plenty of significant information, including a list of challenges and strategies for researchers, organisms with interesting and inspiring biological processes, and lots more. Although the information is not geared towards micro- or nano-processes, it still offers insight into physical systems that sometimes go unnoticed in the animal kingdom.
Even further from microfluidics: Daimler-Chrysler looked to the boxfisha funky fish known for it's boxy shape and thick skinfor inspiration on automotive design, claiming that "the boxfish is... an ideal example of rigidity and aerodynamics." The result is a little odd looking. Regardless of the car's peculiar look, it purportedly performed remarkably well in the wind tunnel, as well as in fuel efficiency and emissions. Here nature proves that this counter-intuitive structure actually provides a useful product. It's remarkable to see biological processes like these inspiring researchers.