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).