Characterizing and Patterning Polyacrylamide Substrates Functionalized with N-Hydroxysuccinimide

Polyacrylamide is a widely used material in cell mechanobiology research. Here, we validate and optimize a method to activate polyacrylamide substrates for protein patterning, resulting in a system with precise and independent control over the geometric and mechanical factors that cells perceive. Acrylic acid incorporated into the hydrogel provides functional sites for activation with N-hydroxysuccinimide, which in turn forms covalent bonds with proteins printed in microscale patterns. To validate and optimize substrate fabrication, we demonstrate that acrylic acid incorporates into the polymer, that is has no effect on Young’s modulus at up to 0.4 wt%, and that increasing concentrations of acrylic acid result in substrates with increasing amounts of protein bound to them. Finally, we demonstrate that cells attach and spread to substrates with protein patterned with electrohydrodynamic jet (e-jet) printing. The method represents an improvement over the most-widely used method to chemically activate polyacrylamide with sulfo-SANPAH. With further refinement, truly independent control over ligand density and stiffness is possible. These substrates are powerful platforms for exploring the interacting influence of substrate stiffness and ligand density on cell behavior.