Rheological fingerprinting of gastropod pedal mucus and bioinspired
complex fluids for adhesive locomotion

Randy Ewoldt,^a Christian Clasen,^b A. E. Hosoi ^a and Gareth H. McKinley*^a

Receipt/Acceptance Data [DO NOT ALTER/DELETE THIS TEXT] 5 Publication data [DO NOT ALTER/DELETE THIS TEXT] DOI: 10.1039/b000000x [DO NOT ALTER/DELETE THIS TEXT]

Nonlinear rheological properties are often relevant in understanding a material’s response to its intended environment, e.g. the physiological or processing conditions of soft condensed matter. Many gastropods crawl on a thin layer of pedal mucus gel using a technique called adhesive locomotion. Adhesive locomotion (of snails or mechanical crawlers) imposes large amplitude pulsatile simple shear flow onto the supporting complex fluid, motivating the characterization of nonlinear rheological properties with large amplitude oscillatory shear (LAOS). This paper compares the rheological fingerprint of native pedal mucus with two bioinspired slime simulants, a carbomer-based polymer gel and a clay-based colloidal gel, in the context of adhesive locomotion of a mechanical system. Native slime is found to exhibit a pronounced strain-stiffening response, which is not imitated by either simulant. The most important property for optimal inclined locomotion is a large, reversible yield stress, followed by a short thixotropic restructuring time.