How to craft actuators and power generators by cutting, folding, and laminating

The functional capabilities of ordinary matter can be greatly enhanced through careful design. A basic example is the bilayer structure, which amplifies small strains into large deformations by harnessing curvature. However, bilayer systems lose their ability to bend when subjected to large loads. Here we use a three-layer design, termed the "Hygrostack," that overcomes the limitation of bilayer designs and show that hygrostacks can carry the advantages of curvature-based design into applications that require large forces and displacements. Using an easy to implement method, we demonstrate large scale (> 1 m) mechanical actuators and sub-Watt scale power generators that use relative humidity differences as the thermodynamic driver. These systems are built from widely available cellulose, plastic, and elastomer sheets, using cutting, folding, and lamination. Our findings show how simple physics principles can greatly expand the capabilities of otherwise ordinary materials.