Snake Skin Tribology

Abstract

Legless locomotion in snakes has an important tribological consequence, as the ventral body side of snakes is almost in continuous contact with the substrate. Propulsion is possible when forward sliding is enabled by a low frictional coefficient, backward slipping is prevented by a high frictional coefficient, and propulsion itself is generated by high transverse frictional forces in lateral directions. Previous experimental data clearly revealed anisotropic friction on the ventral scale surface of snakes. However, it is known that frictional properties of the ventral surface of the snake skin strongly vary, and the degree of anisotropy ranges to a quite strong extent as well. This variation may be explained by (1) different environmental adaptations of the skin surface in various snake species studied, (2) diversity of approaches used for the friction characterization, and (3) a variety of substrates used as a counterpart in the experiments. Snake skin material has a layered structure with graded material properties, which together with specific lipid coatings has an adaptation in reduction of wear in sliding contacts with abrasive environments. This chapter provides an overview of structural, experimental, and numerical studies on interactions between the ventral surface of the snake skin and various substrates. Finally, some biomimetic implications of these results and future perspectives of studies on snake skin tribology are discussed.