Material properties of skin in the flying snake Chrysopelea ornata

Abstract

The genus Chrysopelea encompasses the "flying" snakes. This taxon has the ability to glide via lateral aerial undulation and dorsoventral body flattening, a skill unique to this group, but in addition to other functions common to all colubrids. The skin must be extensible enough to allow this body shape alteration and undulation, and strong enough to withstand the forces seen during landing. For this reason, characterizing the mechanical properties of the skin may give insight to the functional capabilities of the skin during these gliding and landing behaviors. Dynamic and viscoelastic uniaxial tensile tests were combined with a modified particle image velocimetry technique to provide strength, extensibility, strain energy, and stiffness information about the skin with respect to orientation, region, and species, along with viscoelastic parameters. Results compared with two other species in this study and a broader range of species in prior studies indicate that while the skin of these unique snakes may not be specifically specialized to deal with larger forces, extensibility, or energy storage and release, the skin does have increased strength and energy storage associated with higher strain rates. The skin also has differing properties with respect to dorsoventral location, and regional differences in strength in the circumferential orientation. This may indicate that, although the properties of the skin may not be different, the rate at which the skin is strained in the different species may vary, thus altering the apparent properties of the skin during specific behaviors.iii DedicationTo Matthew… For all your love and support, thank you.First, I would like to thank the members of my committee, Dr. Pavlos Vlachos and Dr.Raffaella De Vita for their continuous help throughout this study. I would also like to acknowledge the other members of the DARPA snake team and AEThER lab for their helpful suggestions and assistance with image correlation. Next I must thank, my advisor, Dr. Jake Socha, not only for his for his continual guidance and assistance in this study, but also for helping me to see the bigger picture. I would also like to thank Carolyn Roberts for her assistance with dissection and experimental testing. Funding for this project was provided by DARPA.I would also like to thank my family, biological or not, for constantly encouraging me through this. Lastly, I would like to not only thank anyone who has sent up a prayer for me, but most especially the One answering them. v Table of ContentsDedication .

Functional diversity of snake locomotor behaviors: A review of the biological literature for bioinspiration

“…Beyond friction, a few studies have examined additional mechanical properties of snake skin, such as strength and stiffness, that have functional importance for at least some locomotor behaviors. [264][265][266][267][268] As with many topics in snake biology, the existing literature provides interesting glimpses into structure and function, yet the mechanical properties of snake skin remain a wide-open area for future study. Some trade-offs resulting from skin properties (like structural isotropy/anisotropy) might be inevitable, but snakes may have morphological or behavioral strategies to potentially mitigate trade-offs.…”

“…In contrast, sidewinding requires static (or nearly static) contact with the ground, such that nanostructures promoting isotropy (the same friction coefficient in all directions) enhance sidewinding performance at the expense of lateral undulation 88 (Figure 5). Beyond friction, a few studies have examined additional mechanical properties of snake skin, such as strength and stiffness, that have functional importance for at least some locomotor behaviors 264–268 . As with many topics in snake biology, the existing literature provides interesting glimpses into structure and function, yet the mechanical properties of snake skin remain a wide‐open area for future study.…”