Design and mechanics of complex inflatable networks

The use of compliant materials to accomplish complex movements, made difficult or impossible by rigid materials, has inspired a wide array of soft robots. We have recently introduced “bubble casting”, a novel assembly method that leverages the fluidity of curing silicone elastomers to easily fabricate soft actuators with complex shapes. While liquid, an elastomer is first injected in a tube or tubular mold. An inner void is subsequently sculpted by injecting an elongated bubble into the channels, leaving elastomer only on the channels walls. As the elastomer cures into an elastic solid, gravity passively drains the top part of the channel and lifts the bubble to form the final actuator whose cross-section consists of a thin upper membrane attached to a thick lower beam. Here we explore the mechanical response of our soft actuators: while linear actuators are found to curl when inflated owing the asymmetry of their cross section, the deformation of closed shapes, such as loops, or that of connected networks is more intricate. We will discuss the experimental results we obtained with these programmable robots, and the models we have derived to rationalize our observations.