title: Evidence of a molecular boundary lubricant at snakeskin surfaces.
abstract: During slithering locomotion the ventral scales at a snake's belly are in direct mechanical interaction with the environment, while the dorsal scales provide optical camouflage and thermoregulation. Recent work has demonstrated that compared to dorsal scales, ventral scales provide improved lubrication and wear protection. While biomechanic adaption of snake motion is of growing interest in the fields of material science and robotics, the mechanism for how ventral scales influence the friction between the snake and substrate, at the molecular level, is unknown. In this study, we characterize the outermost surface of snake scales using sum frequency generation (SFG) spectra and near-edge X-ray absorption fine structure (NEXAFS) images collected from recently shed California kingsnake (Lampropeltis californiae) epidermis. SFG's nonlinear optical selection rules provide information about the outermost surface of materials; NEXAFS takes advantage of the shallow escape depth of the electrons to probe the molecular structure of surfaces. Our analysis of the data revealed the existence of a previously unknown lipid coating on both the ventral and dorsal scales. Additionally, the molecular structure of this lipid coating closely aligns to the biological function: lipids on ventral scales form a highly ordered layer which provides both lubrication and wear protection at the snake's ventral surface.
authors.affiliation: School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR 97331, USA.
authors.forename: Joe E
authors.identifier: http://orcid.org/0000-0002-9692-689X
authors.initials: JE
authors.lastname: Baio
authors.affiliation: Functional Morphology and Biomechanics, Zoological Institute, Kiel University, Am Botanischen Garten, Kiel 24118, Germany.
authors.forename: Marlene
authors.initials: M
authors.lastname: Spinner
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD, USA.
authors.forename: Cherno
authors.initials: C
authors.lastname: Jaye
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Fischer
authors.affiliation: Functional Morphology and Biomechanics, Zoological Institute, Kiel University, Am Botanischen Garten, Kiel 24118, Germany.
authors.forename: Stanislav N
authors.initials: SN
authors.lastname: Gorb
authors.affiliation: Max Planck Institute for Polymer Research, 55128 Mainz, Germany weidner@mpip-mainz.mpg.de.
authors.forename: Tobias
authors.initials: T
authors.lastname: Weidner
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D017812:Colubridae; D004817:Epidermis / Q000737:chemistry* / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D054327:Lubricants / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008055:Lipids; D054327:Lubricants
keywords: biomimetic materials; snakeskin; surface chemistry