The master molds used for the fabrication of thermoplastic polymers in both hot embossing and injection molding are usually fabricated by photolithography . Nevertheless, several other fabrication methods such as e-beam writing, electroforming, micro-milling, and electro discharge machining, laser machining, ion machining, additive manufacturing, and ultrasonic machining are applicable for master mold production , as long as the master mold can withstand the high pressures and temperatures used in the hot embossing or micro-injection techniques. Highprecision nickel molds , micro-milled aluminum , and Zr-based bulk metallic glass mold are other master molds used in literature. For instance, a negative master mold was produced in Müller et al.'s work via electroplating Ni on a 3D printed master mold . The negative master mold was then used for creating COC microchannels through injection molding. Hupert et al. used a high-precision micro-milling machine, which had positional and repetition accuracy of ± 1 µm, a laser measuring system and an optical microscope to create microstructures on a brass plate to be employed as a mold for the hot embossing of PMMA substrates . Micro-milling of brass templates has also been performed in other studies to create master molds for hot embossing microchannels in PMMA, PC, and COC substrates . PDMS has also been utilized as a master mold for the fabrication of thermoplastic polymers (Figure e) . In Chantiwas et al.'s study, PDMS master molds were prepared by casting PDMS at a base: curing agent ratio of 10:1 (w:w) in PMMA replicated micro/nano channels 50 . After curing the PDMS and peeling it off, it was used to hot emboss other PMMA substrates under a pressure of 0.16 MPa at 155 ℃ for 30 minutes.