Photolithographically patterned smart hydrogel based bilayer actuators

We describe the fabrication of photopatterned actuators, composed of stimuli-responsive hydrogel bilayers made from N-isopropyl-acrylamide (NIPAm), acrylic acid (AAc), and poly-ethylene oxide diacrylate (PEODA). The hydrogels were deposited by spin coating and casting and were patterned by non-contact photolithography. We investigated the swelling behavior of the individual photopatterned hydrogels in aqueous solutions of varying pH and ionic strength (IS). By combining materials with optimal swelling responses, bilayer structures were triggered via changes in pH and IS to actuate into three dimensional (3D) structures. We also used these hydrogel bilayers as hinges to actuate integrated structures composed of rigid polymeric SU-8 panels, patterned to resemble the shape of a Venus Flytrap. This system provides a straightforward way to design and fabricate actuator hinges composed entirely of polymers.