Soft robotics: Fluid-driven self-folding papers

We demonstrate a self-folding paper robot with capillary force driven fluid. When water is sprayed on fluidic channels patterned on paper, the 2-D sheet of paper can be controllably self-folded into various 3-D structures; half-oval, circle, round-edge square, triangle, half-circle, and table. The self-folding paper sheet can be readily fabricated via a double-sided wax printing method, forming a bilayer structure of the fluidic channel and the hydrophobic wax, in which these two layers have different swelling/shrinking properties. The patterned paper performs folding actuation with water and unfolding behavior with evaporation without being mechanically manipulated by external forces or moments. Finally, we create a paper gripper based on this self-folding actuation, conveying a low-weight object. This report demonstrates the possibility of paper microfluidics for self-folding actuation and soft robotics.