Abstract

The skin is the largest organ in the human body and serves various functions, including mechanical protection and mechanosensation. Yet, even though skin’s biomechanics are attributed to two main layers—epidermis and dermis—computational models have often treated this tissue as a thin homogeneous material or, when considering multiple layers, have ignored the most prominent heterogeneities of skin seen at the mesoscale. Here, we create finite element models of representative volume elements (RVEs) of skin, including the three-dimensional variation of the interface between the epidermis and dermis as well as considering the presence of hair follicles. The sinusoidal interface, which approximates the anatomical features known as Rete ridges, does not affect the homogenized mechanical response of the RVE but contributes to stress concentration, particularly at the valleys of the Rete ridges. The stress profile is three-dimensional due to the skin’s anisotropy, leading to high-stress bands connecting the valleys of the Rete ridges through one type of saddle point. The peaks of the Rete ridges and the other class of saddle points of the sinusoidal surface form a second set of low-stress bands under equi-biaxial loading. Another prominent feature of the heterogeneous stress pattern is a switch in the stress jump across the interface, which becomes lower with respect to the flat interface at increasing deformations. These features are seen in both tension and shear loading. The RVE with the hair follicle showed strains concentrating at the epidermis adjacent to the hair follicle, the epithelial tissue surrounding the hair right below the epidermis, and the bulb or base region of the hair follicle. The regions of strain concentration near the hair follicle in equi-biaxial and shear loading align with the presence of distinct mechanoreceptors in the skin, except for the bulb or base region. This study highlights the importance of skin heterogeneities, particularly its potential mechanophysiological role in the sense of touch and the prevention of skin delamination.

中文翻译：

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界面几何形状和附件对皮肤介观力学的作用

摘要

皮肤是人体最大的器官，具有多种功能，包括机械保护和机械感觉。然而，尽管皮肤的生物力学归因于两个主要层——表皮和真皮——计算模型通常将这种组织视为薄的均质材料，或者在考虑多层时，忽略了在中尺度上看到的最显着的皮肤异质性。在这里，我们创建了皮肤代表性体积元素（RVE）的有限元模型，包括表皮和真皮之间界面的三维变化以及考虑毛囊的存在。正弦界面近似于称为 Rete 脊的解剖特征，不会影响 RVE 的均匀机械响应，但会导致应力集中，特别是在 Rete 脊的山谷处。由于表皮的各向异性，应力分布是三维的，导致高应力带通过一种鞍点连接雷特山脊的山谷。Rete 脊的峰和正弦表面的另一类鞍点在等双轴载荷下形成第二组低应力带。异质应力模式的另一个显着特征是界面上的应力跳跃的切换，随着变形的增加，应力跳跃相对于平坦界面变得更低。这些特征在拉伸和剪切载荷中都可见。毛囊 RVE 显示菌株集中在邻近毛囊的表皮、表皮正下方围绕毛发的上皮组织以及毛囊的球部或基部区域。在等双轴和剪切载荷下，毛囊附近的应变集中区域与皮肤中不同的机械感受器的存在一致，球根或基部区域除外。这项研究强调了皮肤异质性的重要性，特别是其在触觉和预防皮肤分层方面的潜在机械生理作用。