Schulz Andrew K, Plotczyk Magdalena, Sordilla Sophia, Gaboriau David C A, Boyle Madeline, Singal Krishma, Reidenberg Joy S, Hu David L, Higgins Claire A
School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
Department of Bioengineering, Imperial College London, South Kensington, London, SW7 2AZ, UK.
Commun Biol. 2025 Jan 8;8(1):17. doi: 10.1038/s42003-024-07386-w.
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 μm 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 2 mm 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 interactions of 10 μm 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.
如果一种材料坚韧，它通常就缺乏柔韧性，反之亦然。这对于象鼻来说尤为重要，因为象鼻的皮肤既要起到保护作用又要具有弹性。为了探究这是如何实现的，我们使用经典组织化学染色和二次谐波产生显微镜来描述象鼻皮肤的形态和组成。我们报告了从宏观到微观尺度的结构，从真皮的厚度到10微米厚的胶原纤维的相互作用。我们分析了象鼻长度上的几个部位，以比较和对比背腹侧和近远端皮肤的形态和组成。我们发现象鼻的背部皮肤可以有超过2毫米厚的角蛋白铠甲层，这几乎是人类皮肤中同等层厚度的100倍。我们还发现象鼻的结构支撑层（真皮）包含垂直和平行排列的I型胶原（COL1）纤维分布。在象鼻的所有部位都能看到胶原的双峰分布，这与人类皮肤不同，在人类皮肤中，一个方向在身体部位内占主导。我们推测象鼻中COL1的这种分布既赋予了柔韧性又具备承重能力。此外，当观察10微米厚胶原的单个纤维相互作用时，我们发现每单位体积的纤维交叉比人类皮肤中常见五倍，这表明纤维相互缠绕。我们推测这些有趣的结构使象鼻既具有柔韧性又具备强度。象皮的复杂性质可能会启发能够结合强度和柔韧性的材料的设计。
