Nanopatterned PUA-PGMA Substratum Fabrication

A UV-curable poly(urethane acrylate) (PUA, Minutatek, Korea) mold was fabricated using capillary force lithography as published previously^{32 (link),33 (link),35 (link)} and was used as the nanopatterned template for the PUA-PGMA substratum (Figure 1a). To allow for epoxy functionalization of the fabricated nanopatterned substratum, 1% GMA weight/volume monomer (Sigma-Aldrich) was added to the liquid PUA precursor (Norland Optical Adhesive), sonicated for 1 h, and then hand mixed for 10 min. Solution was then degassed under a vacuum for 1 h to remove air bubbles. A glass coverslip (Ø18 mm, Fisher) was cleaned using isopropyl alcohol and brush coated with an adhesion promoter (Glass Primer, Minuta Tech) to allow for attachment of the polymer to the glass surface and air-dried. Twenty microliters of PUA-PGMA prepolymer was added to the coverslip and covered with the PUA template consisting of 800 nm wide and 500 nm deep parallel grooves and ridges. The PUA-PGMA prepolymer was spontaneously drawn into the nanofeatures of the PUA template via capillary force. The template–prepolymer–glass was cured under 365 nm UV light to initiate photopolymerization for 5 min. After polymerization, the PUA template was peeled off from the PUA-PGMA substratum using forceps and the substratum was UV-cured overnight to finalize polymerization.