Enhanced wettability of a SU-8 photoresist through a photografting procedure for bioanalytical device applications

In this work, we detail a method whereby a polymeric hydrogel layer is grafted to negative tone photoresist SU-8 in order to improve its wettability. A photoinitiator is first immobilized on freshly prepared SU-8 samples, acting as the starting point for various surface modification strategies. Grafting of a 2-hydroxyethylmethacrylate-based hydrogel from the SU-8 surface resulted in the reduction of the static contact angle of a water droplet from 79 +/- 1 degrees to 36 +/- 1 degrees, while addition of a poly(ethylene glycol)-rich hydrogel layer resulted in further improvement (8 +/- 1 degrees). Wettability is greatly enhanced after 30 min of polymerization, with a continued but more gradual decrease in contact angle up to approximately 50 min. Hydrogel formation is triggered by exposure to UV irradiation, allowing for the formation of photopatterned structures using existing photolithographic techniques.