In the interest of learning more about biomicrofludics, there will be occasional posts exploring some basics about the subject. Hopefully, these posts will be as useful to non-specialists as they are to me.
One interesting thing about microfluidics (or even nanofluidics) is the method by which small-scale structures are constructed. Even more impressive are some of the images of these structures. At Cornell's Nanofabrication Facility, you'll find a popular example of intricacy and detail. Building three-dimensional microstructures is a bit of art mixed with remarkable technical skills.
To build structures whose vertical dimensions are much larger than their lateral dimensionscalled "high-aspect-ratio micromachining"there are two common tools: X-ray lithography (LIGA, or in German: Lithographi Glvanoformung Abformung) and Deep Reactive Ion Etching (DRIE).
LIGA relies on X-ray lithography and electroplating. Because of the short wavelength of X-rays, they can penetrate a thick photoresist layer while avoiding scattering. LIGA can give an aspect ratio of about 100:1 for vertical to lateral dimensions, and defined features as small as 0.2 micrometers. It might be helpful in this type of description to link to a recent article that uses LIGA. In the Proceedings of SPIE, a recent talk was published from the conference, Device and Process Technologies for Microelectronics, MEMS, Photonics, and Nanotechnology IV, where the authors fabricated a needle array of polycarbonate by using a three-dimensional LIGA process. The needles were 135 μm tall and 50 μm in diameter, and the authors conclude the abstract with: "Thus, we succeeded in extending the LIGA process to a three-dimensional process capability by employing X-ray gray mask." I'd suggest checking out the article if you're interested (maybe even just for the cool SEM images).
Since this post is fairly lengthy already, I'll talk about DRIE in a future post.
A final unrelated comment: It turns out that I may be a little naïve in matters of open-access. After mentioning the apparent successes of the Public Library of Science (PLoS) in my previous post, I stumbled upon some interesting information. It turns out that PLoS isn't sustaining its business model as well as they would like.
PLoS apparently just recently (and without much fanfare) increased their publication rates—again. In 2006, they had pumped up fees from $1500 to $2500 (for their flagship journals PLoS Biology and PLoS Medicine) and to $2000 (for PLoS Computational Biology, PLoS Genetics, and PLoS Pathogens). And now, those journals are apparently getting another bump to $2750 and $2100, respectively. This probably isn't much of a surprise to those within the journal publishing world, but since I’m new you'll have to forgive my naïveté.