Multiscale micro-patterned polymeric and carbon substrates derived from buckled photoresist films: fabrication and cytocompatibility

We report here a novel and simple buckling-based multiscale patterning of negative photoresist films which were subsequently pyrolyzed to yield complex micro-patterned carbon surfaces. Unlike other polymers, the use of a photoresist layer allows the overall pattern definition by photolithography on which the geometry and length scale of the buckling-instability are superimposed. The photoresist film swells anisotropically during developing and buckles after subsequent drying due to the difference in the shrinkage of the hard cross-linked layer on top of a softer native pre-polymer. We studied the conditions for the formation of a wide variety of complex, fractal buckling patterns as well as directionally aligned zigzag patterns over a large area. For example, the buckling diminished for the films below a critical thickness and after a prolonged UV exposure, both of which eliminate the softer under-layer. These patterned carbon substrates are also shown to be biocompatible for the cellular adhesion and viability by using L929 mouse fibroblast cells, thus indicating their potential use in bio-MEMS platforms with a conductive substrate. The buckled carbon patterns were found to be a better choice of a substrate for cell growth and viability as compared to flat and simply periodic patterned carbon surfaces.