Influence of surface morphology and internal structure on the mechanical properties and tribological response of Boa Red Tail and Python Regius snake skin.

The understanding of the tribological behavior of natural structures has been used as inspiration to design and optimize surfaces for diverse applications in engineering. In the present work, morphological, microstructural, mechanical and tribological characterization of the shed skin of two snake species, namely Boa Red Tail and Python Regius was carried out. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) analyses showed the existence of deterministic patterns, i.e., ordered arrays of geometrical features at the surface, while Transmission Electron Microscopy (TEM) allowed studying the internal structure and chemical composition of the skin sheds. Nanoindentation measurements showed significant variations in hardness and elastic modulus from the surface to the inner layers of the skin, and pin-on-disc tests revealed anisotropic behavior of the friction coefficient (COF) as a function of the sliding direction against balsa wood in dry conditions. Correlations between the friction data, nano-indentation mechanical properties and subsurface skin structure were established for both species taking into account the ways in which the skins' deterministic patterns influence the tribological performance.