California blackworms constitute a recently identified animal system exhibiting unusual collective behaviors, in which dozens to thousands of worms entangle to form a “blob” capable of actions like locomotion as an aggregate. In this paper we describe a system of pneumatic soft robots inspired by the blackworms, intended for the study of collective behaviors enabled and mediated by such physical entanglement. Both the robots and worms have high aspect ratio ($\gtrsim 1: 50$), intertwine in complex 3D configurations, operate both in air and underwater, and can locomote both individually and as a collective. We demonstrate and characterize locomotion for both individual robots and entangled blobs, explore the tunability of entanglement strength, and compare these to the analogous versions in living worms. The robots provide a testbed for studying mechanisms underlying behaviors observed in worm blobs, as well as serving as a platform for studies of novel collective behaviors based on physical entanglement.

The performance of inflatable artificial muscles depends greatly on their designs and the output shapes resulting from the geometric constraints. Although there have been attempts to apply physical constraints on the air chamber to achieve larger stroke lengths and increased force-length ratios, it has been difficult to achieve the above two goals while maintaining a compact form factor. In this article, we propose flat inflatable artificial muscles that have large contraction ratios (up to 0.5) and show increased forces in wider ranges of contractions by adding an internal geometric constraint. Addition of an external constraint, such as rigid plates, further increased the maximum contraction ratio (up to 0.553) through a synergistic effect. We show that various force-length relations can be achieved by adjusting the height of the plates. Theoretical models based on the geometry and the principle of virtual work are experimentally validated using actuator prototypes made of heat-sealable plastic sheets. Also, compact capacitive sensors are integrated in design for proprioceptive feedback of the proposed actuators, and their feasibility and effectiveness are experimentally evaluated through closed-loop control.