Woessner Alan E, Jones Jake D, Witt Nathan J, Sander Edward A, Quinn Kyle P
Department of Biomedical Engineering, University of Arkansas, Fayetteville, AR, United States.
Department of Biomedical Engineering, University of Iowa, Iowa City, IA, United States.
Front Bioeng Biotechnol. 2021 Mar 3;9:642866. doi: 10.3389/fbioe.2021.642866. eCollection 2021.
Skin is a heterogeneous tissue that can undergo substantial structural and functional changes with age, disease, or following injury. Understanding how these changes impact the mechanical properties of skin requires three-dimensional (3D) quantification of the tissue microstructure and its kinematics. The goal of this study was to quantify these structure-function relationships second harmonic generation (SHG) microscopy of mouse skin under tensile mechanical loading. Tissue deformation at the macro- and micro-scale was quantified, and a substantial decrease in tissue volume and a large Poisson's ratio was detected with stretch, indicating the skin differs substantially from the hyperelastic material models historically used to explain its behavior. Additionally, the relative amount of measured strain did not significantly change between length scales, suggesting that the collagen fiber network is uniformly distributing applied strains. Analysis of undeformed collagen fiber organization and volume fraction revealed a length scale dependency for both metrics. 3D analysis of SHG volumes also showed that collagen fiber alignment increased in the direction of stretch, but fiber volume fraction did not change. Interestingly, 3D fiber kinematics was found to have a non-affine relationship with tissue deformation, and an affine transformation of the micro-scale fiber network overestimates the amount of fiber realignment. This result, along with the other outcomes, highlights the importance of accurate, scale-matched 3D experimental measurements when developing multi-scale models of skin mechanical function.
皮肤是一种异质性组织，会随着年龄增长、疾病或受伤而发生显著的结构和功能变化。了解这些变化如何影响皮肤的力学性能需要对组织微观结构及其运动学进行三维（3D）量化。本研究的目的是通过对小鼠皮肤在拉伸机械载荷下进行二次谐波产生（SHG）显微镜观察来量化这些结构 - 功能关系。对宏观和微观尺度的组织变形进行了量化，并且在拉伸时检测到组织体积大幅减小以及较大的泊松比，这表明皮肤与历史上用于解释其行为的超弹性材料模型有很大不同。此外，在不同长度尺度之间，测量应变的相对量没有显著变化，这表明胶原纤维网络均匀地分布所施加的应变。对未变形的胶原纤维组织和体积分数的分析揭示了这两个指标都存在长度尺度依赖性。对SHG体积的3D分析还表明，胶原纤维在拉伸方向上的排列增加，但纤维体积分数没有变化。有趣的是，发现3D纤维运动学与组织变形具有非仿射关系，并且微观尺度纤维网络的仿射变换高估了纤维重新排列的量。这一结果以及其他结果突出了在开发皮肤力学功能的多尺度模型时进行准确的、尺度匹配的3D实验测量的重要性。
