Fabrication of high-aspect-ratio hydrogel microstructures

Microfabrication of high-aspect-ratio polymeric microstructures via deep X-ray lithography traditionally involves either crosslinking or scissioning a polymer film spun-cast on a substrate. A post-exposure development procedure is usually employed to remove the unwanted polymer, leaving behind lithographically patterned structures. Instead, we use a novel synthesis technique wherein polymerization of a mixture of monomers in solvent is initiated, through a mask, with hard X-rays. The resulting polymer precipitates out of the solvent, thus limiting the spatial propagation of the reaction only to the exposed regions. Such a technique offers a unique way for the patterned synthesis of polymers from a variety of monomer-solvent systems. Here, we present the first results on the synthesis of high-aspect-ratio microstructures of a thermoreversible hydrogel, poly (N-isopropylacrylamide), and an ionic hydrogel, poly (methacrylic acid). These stand-alone, implantable microstructures are envisioned to be potentially useful in such diverse areas as biosensors, microactuators, controlled release applications, and cell and tissue engineering.