Minsoung Rhee and Mark A Burns. Chemical Engineering, University of Michigan, 2300 Hayward St., 3074 H.H. Dow Building, Ann Arbor, MI 48109
An assembly approach for microdevice construction using prefabricated microfluidic components is presented. Although microfluidic systems are advantageous platforms for biological assays, their use in the life sciences is often limited by the high cost and the level of fabrication expertise required for construction. Assembly blocks act as basic building units to form custom devices. Each Microfluidic Assembly Block (MAB) has a unique function such as inlet/ outlets, valves, straight/curved/bifurcated channels, and chambers. To construct a microfluidic device, selected MABs are assembled to form the desired channel network, as shown in Figure. Non-expert users can assemble the blocks on plain glass slides to build their devices in minutes without the need for expensive design software or clean-room facilities. Fabrication of the MABs involves a multi-step lithography to construct the SU-8 master mold. The master mold is then used to shape the individual assembly blocks. The MAB methodology allows for full flexibility in planar configuration. A simple device can be assembled with square MABs on a glass slide. With simple tweezer manipulations, a fairly good contact between blocks (inter-block gap less than 5 ým) could be repeatedly achieved within seconds. The inherent adhesion between PDMS and glass substrate is reversible and can withstand fluidic pressures high enough to perform typical pneumatically driven flow experiments in biochemical studies. Instead of simple square blocks, another method for block fabrication is to constrain the blocks in pre-defined areas. one of the block-and-base approaches is using cross-shaped alignment posts in PDMS. Such alignment posts tightly confine the block position to enhance alignment. There is another approach with a channeled base and roofed blocks. This channeled base not only defines the position of blocks by PDMS grid walls but also has interconnecting channels for each block in four directions. Such block-and-base systems require more elaborate fabrication procedures to ensure a perfect fit between the blocks and the base. We have used MABs to prototype a variety of microfluidic devices. In addition to fluidic channels, a common component used in microfluidic systems is a PDMS pneumatic valve to control fluid flow. The use of working valve blocks has been demonstrated. A complex system using the zigzag modules to generate molecular gradients is also demonstrated. The system mixes the blue dye and water into an outgoing stream. The use of MABs can be extended to complex biochemical assays. The conceptualized large-scale integration illustrates a system that can perform twenty independent assays simultaneously. The MAB system provides a simple way for non-fluidic researchers to rapidly construct custom, complex microfluidic devices. Non-expert users can also address these channels pneumatically, which enables novel adaptation of digital circuit principles in pneumatically-driven microfluidics. The proposed MAB methodology is thus expected to facilitate the use of a variety of microfluidics devices in the life sciences.