Characterizing the stability of poly-ethylene glycol surface coatings as a function of environmental conditions for micropatterning applications

Poly-ethylene glycol (PEG) is widely used as an antifouling coating in biomedical applications, including the micropatterning of cells, but its anti-fouling properties are known to degrade over time. Here, we systematically characterize the degradation of a methoxy PEG succinimidyl valerate (mPEG-SVA) coating on poly-l-lysine (PLL) treated glass surfaces as a function of temperature and humidity over a 10-week period. This PEG-PLL coating is not as well characterized as coatings of PEG grafted to PLL (PLL-g-PEG), but may offer longer term stability. Using a fluorescence-based method to quantify antifouling efficacy, we found that PEG coatings stored dry at room temperature (25{degree sign}C) exhibited the highest loss of function. In contrast, storing PEG-coated surfaces in phosphate-buffered saline (PBS) at both 4{degree sign}C and 25{degree sign}C, or dry at -20{degree sign}C, effectively preserved their antifouling properties. We used maskless photolithography to selectively degrade PEG, and revealed micro-scale topographical changes in the PEG coating using both fluorescence imaging and atomic force microscopy (AFM). Our findings provide practical guidelines for optimal shipping and storing conditions for PEG-coated substrates.