Long-term stability of grafted polyethylene glycol surfaces for use with microstamped substrates in neuronal cell culture

Crucial to long-term stability of neuronal micropatterns is functional retention of the underlying substratum while exposed to cell culture conditions. We report on the ability of covalently bound PEG films in long-term cell culture to continually retard protein adhesion and cell growth. PDMS microstamps were used to create poly-d-lysine (PDL) substrates permissive to cell attachment and growth, and polyethylene glycol (PEG) substrates were used to minimize protein and cell adhesion. Film thickness was measured using null ellipsometry and atomic force microscopy (AFM). Organosilane film structure was examined using Fourier transform infrared (FT-IR) spectroscopy. Long-term film stability in cell culture conditions was tested by immersion in 0.1 sodium phosphate buffer pH 7.4 for up to one month. Null ellipsometry and water contact measurements indicated that organosilane films were stable up to one month, whereas the PEG film thickness declined rapidly after day 25. Hippocampal cells plated at 200 cells/mm2 on uniform PEG substrates gave a steady increase in biofilm thickness on PEG films throughout the culture, possibly from proteins of neuronal origin. We found that all the layers in the cross-linking procedure were stable in cell culture conditions, with the exception of PEG, which degraded after day 25.