Crawling by traveling deformation of a soft body is a widespread mode of locomotion — from microscopic nematodes, to earthworms, to gastropods. Animals across scales use it to move around different, often challenging environments. Snails, in particular, use mucus — a slippery, aqueous secretion — to control the interaction between their ventral foot and the surface. Their adhesive locomotion has a unique property: it can be used on different surfaces including wood, metal, glass, Teflon (PTFE), or sand in various configurations such as crawling upside-down.
For robotics, low complexity of a single continuous foot could offer resistance to adverse external conditions and wear and tear, while the constant contact with the ground may provide high margins of failure resistance. Adhesive locomotion in robots has been limited to externally powered, centimeter-scale demonstrators with electromechanical drives.
Liquid crystalline elastomers (LCEs) are smart materials that can exhibit macroscopic, fast, reversible shape change under different stimuli including illumination with visible light. They can be fabricated in various forms in the micro-and millimeter scales and, by molecular orientation engineering, can perform complex modes of actuation.
A natural-scale soft snail robot was developed that is based on the optomechanical response of a LCE continuous actuator. The robot propulsion is driven by light-induced traveling deformations of the soft body and their interaction with the artificial mucus layer (glycerin). The robot can crawl at the speed of a few millimeters per minute, about 50 times slower than snails of comparable size, as well as up a vertical wall, on a glass ceiling, and across obstacles.
Despite the slow speed, need of constant lubrication, and low energy efficiency, the elastomer soft robot offers unique insights into micromechanics with smart materials and may also provide a convenient platform for studying adhesive locomotion.