Zhao Y, Feng B, Lee J, Lu N, Pierce D M
Department of Mechanical Engineering, University of Connecticut, Storrs, CT, USA.
Department of Biomedical Engineering, University of Connecticut, Storrs, CT, USA.
J Mech Behav Biomed Mater. 2020 May;105:103694. doi: 10.1016/j.jmbbm.2020.103694. Epub 2020 Feb 17.
Skin wrinkling, especially in the facial area, is a prominent sign of aging and is a growing area of research aimed at developing cosmetics and dermatological treatments. To better understand and treat undesirable skin wrinkles, it is vitally important to elucidate the underlying mechanisms of skin wrinkling, a largely mechanical process. Human skin, a multi-layer composite, has six mechanically distinct layers: from the outermost inward they are the stratum corneum, viable epidermis, dermal-epidermal-junction, papillary dermis, reticular dermis, and hypodermis. To better address the through-thickness hierarchy, and the development of wrinkling within this complicated hierarchy, we established a six-layered model of human skin realized with finite element modeling, by leveraging available morphological and biomechanical data on human skin of the forehead. Exercising our new model we aimed to quantify the effects of three potential mechanisms of wrinkle formation: (1) skin compression due to muscle contraction (dynamic wrinkles); (2) age-related volumetric tissue loss (static wrinkles); and (3) the combined effects of both mechanisms. Since hydration of the stratum corneum significantly affects its stiffness we also aimed to quantify the influence its hydration with these three potential mechanisms of wrinkle formation. Our six-layered skin model, combined with the proposed wrinkling mechanisms, successfully predicts the formation of dynamic and static wrinkles in the forehead consistent with the experimental literature. We observed three wrinkling modes in the forehead where the deepest wrinkles could reach to the reticular dermis. With further refinement our new six-layered model of human skin can be applied to study other region-specific wrinkle types such as the "crow's feet" and the nasolabial folds.
皮肤起皱，尤其是面部皮肤起皱，是衰老的一个显著标志，也是化妆品和皮肤病治疗研发领域中一个不断发展的研究方向。为了更好地理解和治疗不良皮肤皱纹，阐明皮肤起皱的潜在机制至关重要，因为这在很大程度上是一个机械过程。人类皮肤是一种多层复合材料，有六个机械特性不同的层：从最外层向内依次是角质层、有活力的表皮、真皮 - 表皮连接、乳头层真皮、网状层真皮和皮下组织。为了更好地处理整个厚度层次结构以及在这个复杂层次结构中皱纹的形成，我们利用前额皮肤现有的形态学和生物力学数据，通过有限元建模建立了一个六层人类皮肤模型。运用我们的新模型，我们旨在量化三种潜在皱纹形成机制的影响：（1）肌肉收缩导致的皮肤压缩（动态皱纹）；（2）与年龄相关的组织体积损失（静态皱纹）；（3）两种机制的综合影响。由于角质层的水合作用会显著影响其硬度，我们还旨在量化其水合作用对这三种潜在皱纹形成机制的影响。我们的六层皮肤模型，结合所提出的皱纹形成机制，成功地预测了前额动态和静态皱纹的形成，与实验文献一致。我们在前额观察到三种皱纹模式，其中最深的皱纹可延伸至网状层真皮。通过进一步完善，我们新的六层人类皮肤模型可应用于研究其他特定区域的皱纹类型，如“鱼尾纹”和鼻唇沟。
