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 antifouling properties are known to degrade over time. Here, we systematically characterize the degradation of a methoxy PEG succinimidyl valerate coating on poly-l-lysine (PLL) treated glass surfaces as a function of temperature and humidity over a 10-week period. This PEG functionalization strategy is not as well-characterized as the more established PEG grafted to PLL (PLL-g-PEG) coating, 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°C) exhibited the highest loss of function. In contrast, storing PEG-coated surfaces in phosphate-buffered saline at both 4 and 25°C, or dry at −20°C, effectively preserved their antifouling properties. We used maskless photolithography to selectively degrade PEG and revealed micro-scale and chemical changes in the PEG coating using fluorescence imaging, mass spectrometry, and atomic force microscopy. Our findings provide practical guidelines for optimal shipping and storing conditions for PEG-coated substrates.