Light-steerable locomotion using zero-elastic-energy modes.

Driving synthetic materials out of equilibrium via dissipative mechanisms paves the way towards autonomous, self-sustained robotic motions. However, obtaining agile movement in diverse environments with dynamic steerability remains a challenge. Here we report a light-fuelled soft liquid crystal elastomer torus with self-sustained out-of-equilibrium movement. Under constant light excitation, the torus undergoes spontaneous rotation arising from the formation of zero-elastic-energy modes. By exploiting dynamic friction or drag, the zero-elastic-energy-mode-based locomotion direction can be optically controlled in various dry and fluid environments. We demonstrate the ability of the liquid crystal elastomer torus to laterally and vertically swim in the Stokes regime. The torus navigation can be extended to three-dimensional space with full steerability of the swimming direction. These results demonstrate the possibilities enabled by prestrained topological structures towards robotic functions of out-of-equilibrium soft matter.