Material properties of the skin of the Kenyan sand boa Gongylophis colubrinus (Squamata, Boidae).

On the basis of structural data, it has been previously assumed that the integument of snakes consists of a hard, robust, inflexible outer surface (Oberhäutchen and beta-layer) and soft, flexible inner layers (alpha-layers). The aim of this study was to compare material properties of the outer and inner scale layers of the exuvium of Gongylophis colubrinus, to relate the structure of the snake integument to its mechanical properties. The nanoindentation experiments have demonstrated that the outer scale layers are harder, and have a higher effective elastic modulus than the inner scale layers. The results obtained provide strong evidence about the presence of a gradient in the material properties of the snake integument. The possible functional significance of this gradient is discussed here as a feature minimizing damage to the integument during sliding locomotion on an abrasive surface, such as sand.