Figure 2.

Fabrication methods for microfluidic devices. (a) Photolithography involves using a transparency mask to pattern UV light and resultant crosslinking of photoresist, which is a photosensitive polymer (sample image of a silicon master fabricated with photolithography modified from [45]). (b) Soft lithography involves casting an elastomer on a master mold to create a negative copies of the master for use as a final microfluidic device (example of PDMS device modified from [168]). (c) Embossing is an alternative replica molding approach in which thermoplastic materials are heated and pressed against a master mold to form negative copies (example of thermoplastic device modified from [169]). (d) Laser cutting, milling, and cutting are methods for removing material from bulk plastic to directly fabricate channels or to create a master mold (example of micromilled channel modified from [170]). (e) Lamination involves bonding individual layers with heat and pressure to create multilayer devices (example of multichannel device modified from [68]). (f) 3D printing involves fabricating devices or molds through additive processes. Fused deposition modeling (FDM) involves directly patterning material ejected from a nozzle, and stereolithography (SLA) uses a laser or focused light source and movable stage to crosslink resin and build structures with 3D resolution (sample multicomponent device modified from [171]).