Photothermally-driven oxazine hydrogel actuators at the water-air interface

The design of synthetic hydrogels capable of exhibiting smart adaptive behaviors in response to light has gained significant interest to mimic the dynamic structures and functions as we observed in nature. Here we report on the molecular design of a photoresponsive hydrogel by covalently integrating oxazine-based compounds into the crosslinked polymer network through a free radical copolymerization strategy. The resultant oxazine hydrogels are found to be able to display well-controlled temperature variation through a photothermal effect in response to external irradiation with visible light. The light-induced non-uniform temperature variation of these hydrogels at the water-air interface lead to the generation of Marangoni propulsion, which subsequently drives them move as a swimmer. In addition to unidirectional swimming, such hydrogel swimmers are able to display steering, rotating, path-following motion and cargo transporting function by control of external irradiation parameters. Our work provides a useful molecular design strategy for development of other photoactive hydrogels with applications in smart actuators and soft robotics.