Fig. 2.

Linear zigzag actuators made of a variety of materials using different fabrication methods. (A) A transparent actuator lifts a clear acrylic plate. Skeleton material ($SkeM$): 0.254 mm transparent polyester sheet. Fabrication method ($FM$): laser cutting and manual folding. Skin material ($SkiM$): 0.102 mm transparent PVC film (Vinyl). Driving fluid ($DF$): air. (B) A soft linear actuator contracts well even when it is confined into a metal screw nut. $SkeM$: silicone rubber (M4601). $FM$: casting. $SkiM$: 0.24 mm TPU film. $DF$: air. (C) A vacuum-driven water-soluble actuator is dissolved in hot water (≈ 70 °C) within 5 min. $SkeM$: polyvinyl alcohol (PVA). $FM$: 3D printing. $SkiM$: 0.025 mm PVA film. $DF$: air. (D) A water pump-driven hydraulic actuator pulls an underwater object for 3.5 cm in 20 s. $SkeM$: 0.254 mm stainless steel (316). $FM$: manual forming. $SkiM$: 0.24 mm TPU film. $DF$: water.