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

Abstract

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 (∼20μm 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 ∼15μm gap. A shaft with a diameter of ∼25μm 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 ∼100μm) 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 ∼150μm) 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.