Meeting Abstract

S5.2-4  Sunday, Jan. 5 11:30  Bone-free: Soft Mechanics for Adaptive Locomotion TRIMMER, B.A.; Tufts University

Both muscular hydrostats (such as mollusks) and fluid-filled animals (such as annelids) exploit their constant volume tissues to transfer forces and displacements as articulated animals use hinges and levers. However, body control is more complicated for soft animals with layers of muscle oriented in multiple planes or with compressible tissues. Using caterpillars as a tractable model system it is now possible to identify the novel biomechanical and neural strategies for controlling movements in a highly deformable animal. For example, Manduca sexta , can stiffen by increasing muscular tension (and therefore body pressure) but the internal body cavity (hemocoel) is not iso-barometric nor is pressure used to directly control the movements of its limbs. Instead fluid and tissues flow within the hemocoel and the body is soft and flexible to conform to the substrate. During crawling the body is kept in tension for part of the stride and compressive forces are exerted on the substrate along the axis of the caterpillar (an “environmental skeleton”). The timing of muscle activity suggests that crawling is coordinated by proleg retractor motoneurons and that the large segmental muscles produce anterograde waves of movement requiring little timing precision. This strategy produces a robust form of locomotion in which the kinematics changes very little with orientation. In different species of caterpillar the presence of prolegs on particular body segments is related to alternative kinematics such as “inching”. Some of these findings are being used to design and test novel control strategies for highly deformable robots. These “Softworm” devices are providing new insights into the challenges faced by any soft animal navigating in a terrestrial three-dimensional world.