Multimaterial polyacrylamide: fabrication with electrohydrodynamic jet printing, applications, and modeling.

Micropatterned, multimaterial hydrogels have a wide range of applications, including the study of microenvironmental factors on cell behavior, and complex materials that rapidly change shape in response to fluid composition. This paper presents a method to fabricate microscale polyacrylamide features embedded in a second hydrogel of a different composition. An electrohydrodynamic jet (e-jet) printer was used to pattern hemispherical droplets of polyacrylamide prepolymer on a passive substrate. After photopolymerization, the droplets were backfilled with a second polyacrylamide mixture, the second mixture was polymerized and the sample was peeled off the substrate. Fluorescent and confocal microscopy confirmed multimaterial patterning, while scanning probe microscopy revealed a patterned topography with printed spots forming shallow wells. Finite element modeling was used to understand the mechanics of the formation of the topographical features during backfill and subsequent polymerization. Finally, polyacrylamide containing acrylic acid was used to demonstrate two applications of the micropatterned hydrogels: stimuli-responsive materials and patterned substrates for cell culture. The e-jet fabrication technique described here is a highly flexible, high resolution method for creating multimaterial hydrogels.