PADeMIS shall move in a tube like environment and be supported by the dura and the vertebral body. The structure of PADeMIS should be compliant and the environment contact should be on a large area. Therefore, creeping and crawling of worms, larvae, snails, maggots and snakes could be used as biological inspiration. The most promising locomotion type for the application in the spinal canal is the - earthworm like - peristaltic locomotion. The technical realisation is shown in the patent of Zimmermann et. al., 2000. Following up the locomotion of the earthworm, the technical peristaltic motion and for comparison the inch worm motion is explained here:

Locomotion of the earthworm (Annelida)
Waves of contraction and relaxation of alternate muscle groups (longitudinal and circular muscles) are causing the worm to move forward. Four pairs of bristles at each segment can be elevate for anchor the temporary immobile segments. The body cavity is fluid-filled and partitioned into numerous separate segments. The hydrostatic skeleton counteracts the muscle movements.

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Peristaltic locomotion
The locomotion is based on a propagating wave on the surface of the moving device. Technologically a segmentation of the body is useful. The simplest functional unit for a peristaltic moving device is a structure with 3 segments - each segment allowing thickening and lengthening at the same time. Also any other unit with more than 3 elements is possible. A serial arrangement of these kind of units is possible. A "step" in a peristaltic motion of a unit with n elements is made by n switching operations. At least 2 elements in the functional unit have to be controlled simultaneously. The step length is the length difference between the small and big size of one element multiplied by the number of small elements in the functional unit. Changing the length of the functional unit is possible. A structure with - for example - 18 elements can be controlled with functional units of length 3, 6, 9 or 18.

Peristaltic motion with 3 Elements

Peristaltic motion with 6 Elements


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An inch-worm is build up by alternating thickening and lengthening elements.The smallest functional unit is made of 3 elements - 1 for lengthening and 2 for thickening. A serial combination of this units needs another lengthening element, then the functional unit contains 4 elements. An inch- worm with 3 elements can be controlled by each segment separately. For a serial structure, simultaneous controll of 2 elements in the functional unit is necessary. An inch- worm needs 6 switching operations for one step. The step length is the length difference between the short and long state of the lengthening element.

For the following reasons peristaltic locomotion is chosen for PADeMIS:

For questions or comments, please contact: pademis@tu-ilmenau.de