Master mold for PDMS imprinting

SU-8 resin (GM-1075, Gersteltec, Switzerland) was spin-coated at 1030 rpm for 50 s onto a clean Si wafer. The soft bake was done over 1 hour at 120°C using a 4°C/min ramp. The SU-8 film was then exposed using a dedicated Cr-Mask and a Mask Aligner (MA6-Gen3, Süss MicroTec, Germany), using a dose of 528 mJ/cm². Post-exposure bake was done for 2 hours at 90°C. Development was done using Poly(ethylene glycol) methyl ether acrylate (PEGMEA) for 3 min and further rinsed using isopropanol for 2 min. The resulting SU-8 pillars were silanized using trichloro-(perfluorooctyl)silane (Sigma-Aldrich, USA). Textured PDMS substrates were made by drop-casting SYLGARD 184 (Dow Chemical) over the previously described SU-8 structures, using a 10:1 monomer/curing agent ratio. The PDMS was placed under vacuum for 20 min before the curing step at 80°C for 24 hours.