2.3.1 Fabrication of the microfluidic mold
Standard UV-photolithography and replica molding were employed to fabricate the mold. Briefly, a microfluidic channel with a serpentine morphology was designed by CAD software (AutoCAD, Autodesk) containing channels of 200 µm in width, mimicking the tortuous morphology of the tumor microvasculature. Next, SU8-2010 photoresine (Microchem) was spin-coated on top of a Si wafer to obtain a thickness of 100 um. A mask aligner (MDA-400M, MIDAS) was used to UV-irradiate the coated Si wafer, removing the non-exposed areas with SU-8 developer (Michochem). The resulting SU8 mold was silanized with trichloro(1H,1H,2H,2H-perfluorooctyl)silane (TCS; Sigma) by vapor phase for 1 h, and cured at 70ºC for 1 h and replicated in PDMS (10:1 w/w pre-polymer: crosslinker; Sylgard 184 Dow Corning). After pouring the PDMS, the mixture was degassed in a vacuum chamber and cured at 70°C for 2 h, resulting in a negative PDMS replica. Next, this mold was O2 plasma-activated, silanized with TCS for 1 h under a vacuum, and replicated again in PDMS (10:1 w/w) to generate the final mold for pouring the eSF solution and obtaining the hydrogel microfluidic chip.