In recent years microfabricated devices have been developed for cell culture applications (El-Ali et al., 2006; Taylor et al., 2005; Taylor et al., 2003). These devices are precisely and reproducibly fabricated with features that are on a similar physical scale to cells. The properties of fluid at the microscale allow the creation of precise microenvironments, such as concentration gradients (Jeon et al., 2002) or fluidically-isolated subcellular compartments (Taylor et al., 2005; Taylor et al., 2003). The most common method for fabricating microfluidic devices for biological applications uses photolithography to create a master or template using the epoxy photoresist, SU-8. SU-8 polymerizes when exposed to ultraviolet light and can be used to create relatively high structures, in the range of hundreds of microns, which are suitable for cell culture. After the template is produced, it can then be used indefinitely to replica mold the microfluidic devices using poly(dimethylsiloxane) (PDMS), a biocompatible, optically transparent polymer. This process, called soft lithography, is cost effective and can be performed in any traditional lab setting (McDonald et al., 2000; Whitesides et al., 2001).
