Meeting Abstract
To successfully traverse dissipative environments, slithering animals (e.g., snakes, nematodes) must generate appropriate reaction forces to overcome friction. In yielding substrates (e.g., sand) where there is permanent deformation post interaction, maneuverability is essential in order to overcome heterogeneities. In particular, the mm-long nematode worm C. elegans is able to traverse complex environments by using complex steering behaviors without being hindered by heterogeneities. While this worm is the subject of thousands of studies, few have focused on how it performs and controls self-propulsion. To discover principles of nematode control and steering, we conducted experiments in fluid-filled PDMS lattice of posts. We induced escape responses in the lattices via localized thermal stimuli to C. elegans with a NIR laser diode (Mohammadi et al, 2013). When stimulated in the head, worms respond by escaping from the thermal source via backing up, self-deforming the body to an omega-like shape for reorientation (known as an omega turn) and moving forward, previously studied in detail in homogeneous environments. This was surprising as we expected omega turns in the lattice to be hindered by obstacles. However, performance was comparable to that on the surface of homogeneous agar plates. A geometric mechanics framework rationalized the observed biological turn dynamics. We posit omega turns are a robust way to turn and maneuver in complex environments. Inspired by the worms capabilities in heterogeneous environments, we developed a robot controller to enable maneuvering in lattices via a scheme which senses joint torques to enable shape-based compliance control.
