| AVS 62nd International Symposium & Exhibition | |
| Biomaterial Interfaces | Wednesday Sessions |
| Session BI-WeM |
| Session: | Biomolecules at Interfaces |
| Presenter: | Joe Baio, Oregon State University |
| Authors: | J.E. Baio, Oregon State University M. Spinner, University of Kiel, Germany C. Jaye, National Institute of Standards and Technology (NIST) D.A. Fischer, National Institute of Standards and Technology (NIST) S. Gorb, University of Kiel, Germany T. Weidner, Max Planck Institute for Polymer Research, Germany |
| Correspondent: | Click to Email |
Snake scales have direct mechanical interaction with the environment. During slithering the ventral scales at a snake’s belly are permanently in contact with the substrate, while the dorsal scales have an optical function for camouflage and thermoregulation. Recently it has been shown that ventral scales have adapted to this biological function and provide improved lubrication and wear protection compared with dorsal scales. While biomechanic adaption of snake motion to specific habitats is of growing interest in material science and robotics, the molecular level mechanism for the frictional influence of ventral scales 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 freshly molted California kingsnake (Lampropeltis californiae) scales. NEXAFS microscopy enables the mapping of specific molecular bonds at the C and N K-edges. The resulting NEXAFS images highlight the intensities of C=C π*, σ* (C−H), C=O π*, and amide π* bonds, demonstrating that the chemistry across the scale surfaces is uniform. SFG spectra at the amide I vibrational band (1550-1850 cm-1) were collected from ventral and dorsal scales across three different individuals. Within the spectra taken from both types of scales, we observe a single peak at 1746 cm-1 that originates from ordered ester groups. In the CH stretching region, we observe two distinct vibrational modes in the spectra collected from the dorsal scale - 2850 and 2865 cm-1. Both of these modes stem from symmetric CH2 vibrations. Three bands are present in the CH spectra from the ventral scale - 2850, 2875, and a broad peak at 2975 cm-1. Again, the peak at 2850 cm-1 is related to CH2 symmetric vibrations, while the peaks at 2875 and 2975 cm-1 are related to symmetric and in plane anti-symmetric CH3 stretches, respectively. Combined this analysis reveals the existence of a previously unknown lipid coating on the surfaces of both the ventral and dorsal scales with molecular structure closely related to their biological function: lipids on ventral scales form a highly ordered layer which provides both lubrication and wear protection at the snake’s ventral surface.