Imaging surface immobilization chemistry: correlation with cell patterning on non-adhesive hydrogel thin films.

High-fidelity surface functional group (e.g., N-hydroxysuccinimide (NHS) reactive ester) patterning is readily and reliably achieved on commercial poly(ethylene glycol) (PEG)-based polymer films already known to exhibit high performance non-fouling properties in full serum and in cell culture conditions. NHS coupling chemistry co-patterned with methoxy-capped PEG using photolithographic methods is directly spatially imaged using imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) and principal components statistical analysis. Patterned NHS surface reactive zones are clearly resolved at high sensitivity despite the complexity of the polymer matrix chemistry. ToF-SIMS imaging also reveals the presence of photo-resist residue remaining from typical photolithography processing methods. High cross-correlation between various ion-derived ToF-SIMS images is observed, providing sensitive chemical corroboration of pattern chemistry and biological reactivity in complex milieu. Surface-specific protein coupling is observed first by site-selective reaction of streptavidin with NHS patterns, followed by identical patterns of biotinylated Alexa-labeled albumin coupling. This suggests that streptavidin immobilized on the patterns remains bioactive. Fluorescently labeled full serum is shown to react selectively with NHS-reactive regions, with minimal signal from methoxy-capped regions. Insufficient serum is adsorbed under any conditions to these surfaces to support cell attachment in serum-containing media. This reflects the high intrinsic non-adsorptive nature of this chemistry. Fibroblasts attach and proliferate in serum culture only when a cell adhesion peptide (RGD) is first grafted to NHS regions on the PEG-based surfaces. Longer-term serum-based cell culture retains high cell-pattern fidelity that correlates with chemical imaging of both the NHS and RGD patterns and also lack of cell adhesion to methoxy-capped regions. Cell staining shows orientation of adherent cells within the narrow patterned areas. Cell patterns are consistently retained beyond 15 days in serum media.