Data from: Second harmonic generation imaging reveals entanglement of collagen fibers in the elephant trunk skin dermis

Form-function relationships often have tradeoffs: if a material is tough,
it is often inflexible, and vice versa. This is particularly relevant for
the elephant trunk, where the skin should be protective yet elastic. To
investigate how this is achieved, we used classical histochemical staining
and second harmonic generation microscopy to describe the morphology and
composition of elephant trunk skin. We report structure at the macro and
micro scales, from the thickness of the dermis to the interaction of 10
micro-m thick collagen fibers. We analyzed several sites along the length
of the trunk to compare and contrast the dorsal-ventral and
proximal-distal skin morphologies and compositions. We find the dorsal
skin of the elephant trunk can have keratin armor layers over 2mm thick,
which is nearly 100 times the thickness of the equivalent layer in human
skin. We also found that the structural support layer (the dermis) of the
elephant trunk contains a distribution of collagen-I (COL1) fibers in both
perpendicular and parallel arrangement. The bimodal distribution of
collagen is seen across all portions of the trunk, and is dissimilar from
that of human skin where one orientation dominates within a body site. We
hypothesize that this distribution of COL1 in the elephant trunk allows
both flexibility and load-bearing capabilities. Additionally, when viewing
individual fiber interaction of 10 micro-m thick collagen, we find the
fiber crossings per unit volume are five times more common than in human
skin, suggesting that the fibers are entangled. We surmise that these
intriguing structures permit both flexibility and strength in the elephant
trunk. The complex nature of the elephant skin may inspire the design of
materials that can combine strength and flexibility.