Underwater motion of hydrogel microstructure by optofluidic lithography studied with gap control and object holding platform

Free floating microstructures are obtained by optofluidic lithography on a photocurable hydrogel in a microchannel. Such hydrogel-based components are expected to work in water for the actuation of movable components in biomedical applications. This paper reports the underwater motion of a hydrogel microstructure patterned by optofluidic lithography, studied with a platform that anchors an object and controls the gap between the gel and the channel. First, the authors developed this platform composed of three layers of polydimethylsiloxane (PDMS); a thin PDMS membrane (similar to 20 mu m thick) is sandwiched between the two outer layers and pneumatically actuated to decrease the thickness of the photocurable resin solution in a top microchannel, which leads to similar to 15 mu m gap. A shaft with a diameter of similar to 25 mu m on the membrane enables the fabricated object to be kept in the same place when the surrounding solution is changed. Second, the authors studied the effect of surfactant Triton X on the motion of the hydrogel object with the developed platform. A microgear (outer diameter similar to 100 mu m) composed of photocurable hydrogel containing Triton X was formed and moved in a deionized water stream. After the effect of Triton X was lost, the gear stopped its movement in water. Addition of Triton X solution restarted the motion of the gear. A rod hydrogel structure (total length similar to 150 mu m) formed without Triton X did not move in the deionized water. These results show that a surfactant is essential to move a hydrogel structure in water. Our findings are useful for the actuation of movable parts in water and in future biomedical applications. (C) 2016 Elsevier B.V. All rights reserved.