School of Mechanical Engineering, Purdue University, AB Tepole, 585 Purdue Mall, West Lafayette, USA.
Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, USA.
Biomech Model Mechanobiol. 2024 Apr;23(2):553-568. doi: 10.1007/s10237-023-01791-6. Epub 2023 Dec 21.
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.
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匀材料，或者在考虑多层时，忽略了皮肤在介观尺度上最明显的异质性。在这里，我们创建了皮肤的代表性体积元（RVE）的有限元模型，包括表皮和真皮之间界面的三维变化，以及考虑到毛囊的存在。正弦界面近似于称为网脊的解剖特征，不会影响 RVE 的均匀力学响应，但会导致应力集中，特别是在网脊的山谷处。由于皮肤的各向异性，应力分布是三维的，导致通过一种类型的鞍点连接网脊山谷的高应力带。网脊的峰和正弦表面的另一种鞍点类形成了在等双轴加载下的第二组低应力带。异质应力模式的另一个突出特征是界面处的应力跳跃发生变化，随着变形的增加，相对于平面界面，应力跳跃会降低。这些特征在拉伸和剪切加载中都可见。带有毛囊的 RVE 显示出在毛囊附近的表皮、位于表皮下方的毛囊周围的上皮组织以及毛囊的球部或基部区域集中的应变。在等双轴和剪切加载下，毛囊附近的应变集中区域与皮肤中存在的独特机械感受器相对应，除了球部或基部区域。这项研究强调了皮肤异质性的重要性，特别是其在触觉感知和预防皮肤分层方面的潜在机械生理学作用。
