Lubrication Behavior of Slug Mucus

Crawling worms such as slugs are natural tribological species able to deal with varied surface textures as they crawl. Slug mucus has the ability to act as both an adhesive and a lubricant. In order to understand the principles behind slugs’ crawling motion, the frictional behavior of slug mucus was studied, as well as its rheological and morphological properties. The solid constituents of the mucus were confirmed by means of nuclear magnetic resonance. A shear thinning behavior was observed using a rheometer. Slug mucus has a low friction coefficient, and the presence of water enhanced its capacity as a lubricant. The nano-scale physical structure of the solid constituents of the slug mucus was determined by means of atomic force microscopy. It was found that the macro-scale shear thinning behavior works in conjunction with the slug’s method of locomotion to provide lubrication for sliding and gel-like adhesion. This overlooked animal might offer a world of intelligent design in engineering biomimetic systems that can both adhere and slide simultaneously. Furthermore, biodegradable and water-compatible features of slug mucus shed light on the formulation of a new generation of lubricants.