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Folding Sleeves — Variations on a Theme of the Earthworm

The earthworm is a pressurised fluid tube whose peristaltic locomotion is facilitated by distinct structural features. The envelope of the earthworm incorporates two primary morphological and structural systems: A skeletal system, formed by a helical network of collagen fibres, and a continuous system composed of a stretchable membrane. The two systems closely interact under internal fluid pressure to produce the peristaltic locomotion. The paper presents applications of foldable sleeves or tubes, simulating the morphological and kinematical aspects of the earthworm locomotion, focusing on the combination of skeletal and compatible stressed-skin systems to produce a functional envelope. Several skeletal and stressed-skin structural systems and their combinations are presented, making extensive use of physical models. These systems are characterised by helical morphological features, which preserve the main kinematical characteristics of earthworm locomotion.