Lab-scale prototyping of polymer based microfluidic devices using gallium as phase-changing sacrificial material

We present a fabrication method for polymer based microfluidic devices using gallium as a sacrificial material during the sealing process based on solvent bonding, allowing for lab-scale prototyping of microfluidic chips. The microfluidic channels are structured by laser engraving of poly(methyl methacrylate) (PMMA) sheets. The devices are temporarily closed by clamping the engraved parts on a flat surface with a thin polymer film in between. Liquid gallium is then injected into the temporarily sealed channels and is subsequently cooled to form a solid sacrificial layer preventing clogging and distortion of the microchannels during the subsequent bonding process. After finally sealing the device, it is warmed up to liquefy the gallium, which is then flushed from the channels. The feasibility of this approach is demonstrated by fabricating a microfluidic flow focusing device and a chemical gradient generator. The proposed method using gallium features distinct advantages compared to previously reported similar approaches that successfully make use of, e.g., wax, hydrogels or water as sacrificial materials.