Composition-tunable properties of amphiphilic comb copolymers containing protected methacrylic acid groups for multicomponent protein patterning

Methods to micropattern multiple protein components on surfaces under mild conditions are of interest for biosensing, proteomics, and fundamental studies in cell biology. Here, we report on the composition-dependent thin-film solubility behavior of o-nitrobenzyl methacrylate (oNBMA, a protected form of methacrylic acid)/methyl methacrylate (MMA)/poly(ethylene glycol) methacrylate (PEGMA) random terpolymers, materials which are promising as aqueous-processible photoresists. Over a broad range of terpolymer compositions, these materials formed initially water-insoluble films, which, upon UV irradiation, rapidly dissolved in aqueous solutions above a critical pH. This threshold pH ranged from approximately 5-7 depending upon the copolymer composition and decreased as the relative ratio of MMA to PEGMA in the copolymers decreased. In addition, in a narrow window of compositions near 35:0:65 oNBMA/MMA/PEGMA (wt ratio), an inverse behavior was observed: thin films that were initially water soluble became kinetically stable in aqueous solutions after UV exposure. The time for these films to completely dissolve was hours rather than seconds, and the rate of dissolution was both temperature- and pH-dependent. This behavior is consistent with a transient stability imparted by inter- and intramolecular hydrogen bonding in the film. Using copolymers of this composition as negative tone photoresists, we demonstrated patterning of two proteins into two discrete regions of a surface. The selective solubility of the resist copolymer allows the entire patterning process to be completed using only biological buffers as solvents and across a temperature range between 4 and 37 degrees C without subjecting either protein to ultraviolet irradiation or dehydration. These materials are thus of interest for complex surface photopatterning under mild aqueous conditions.