Fabrication of biodegradable electrohydraulic soft actuators
The fabrication process is illustrated in Figure S1 and Figure S2. For the linear-type actuators, two layers of biodegradable dielectric film were bonded by thermobonding. This was done using a 3D printer (Flashforge 3D technology, Adventurer 3). The print head nozzle of the 3D printer was heated to 180°C, and the platform was kept at 50 °C. By moving the head nozzle while keeping in contact with the dielectric film layers, a pouch of the designed dimensions was fabricated. Then, soybean oil was injected into the pouch. The amount of oil used was 1.4 mL. The gelatin-based electrode was prepared using the same steps as used in the fabrication of samples for the resistivity measurement. The gelatin solution heated at 80°C for 1 h was blade-casted on a plastic substrate using a film applicator (Industrial Physics, TQC Sheen) and an applicator coater (Zehntner, ZUA 2000), forming an electrode layer with a thickness of 143 μm after curing at room temperature for 24 h at 23°C (67% RH). Then, the casted electrode layer was cut using a plotter cutter (Graphtec, CE6000-40 Plus). The electrode was attached to the pouch made of biodegradable layers and corn starch powder was coated on it. The fabrication process of the circular-type actuators was the same as that of the linear-type, except for the amount of oil used (2 ml and 4 ml) and the thickness of the electrode layer (50 μm).