The intact and healthy skin forms a barrier to the outside world and protects the body from mechanical impact. The skin is a complex structure with unique mechano-elastic properties. To better direct the design of biomimetic materials and induce skin regeneration in wounds with optimal outcome, more insight is required in how the mechano-elastic properties emerge from the skin’s main constituents, collagen and elastin fibers. Here, we employed two-photon excited autofluorescence and second harmonic generation microscopy to characterize collagen and elastin fibers in 3D in 24 human dermis skin samples. Through uniaxial stretching experiments, we derive uni-directional mechanical properties from resultant stress-strain curves, including the initial Young’s modulus, elastic Young’s modulus, maximal stress, and maximal and mid-strain values. The stress-strain curves show a large variation, with an average Young’s modules in the toe and linear regions of 0.1 MPa and 21 MPa. We performed a comprehensive analysis of the correlation between the key mechanical properties with age and with microstructural parameters, e.g., fiber density, thickness, and orientation. Age was found to correlate negatively with Young’s modulus and collagen density. Moreover, real-time monitoring during uniaxial stretching allowed us to observe changes in collagen and elastin alignment. Elastin fibers aligned significantly in both the heel and linear regions, and the collagen bundles engaged and oriented mainly in the linear region. This research advances our understanding of skin biomechanics and yields input for future first principles full modeling of skin tissue.

完整健康的皮肤形成了与外界的屏障，保护身体免受机械冲击。皮肤是一种复杂的结构，具有独特的机械弹性特性。为了更好地指导仿生材料的设计并诱导伤口皮肤再生以获得最佳结果，需要更多地了解皮肤的主要成分胶原蛋白和弹性蛋白纤维如何产生机械弹性特性。在这里，我们采用双光子激发自发荧光和二次谐波产生显微镜来表征 24 个人类真皮样品中的胶原蛋白和弹性蛋白纤维的 3D 特征。通过单轴拉伸实验，我们从所得的应力-应变曲线中得出单向力学性能，包括初始杨氏模量、弹性杨氏模量、最大应力以及最大和中间应变值。应力-应变曲线显示出较大的变化，趾部和线性区域的平均杨氏模量为0.1 MPa 和21 MPa。我们对关键机械性能与老化和微观结构参数（例如纤维密度、厚度和取向）之间的相关性进行了全面分析。研究发现年龄与杨氏模量和胶原蛋白密度呈负相关。此外，单轴拉伸期间的实时监测使我们能够观察胶原蛋白和弹性蛋白排列的变化。弹性蛋白纤维在脚跟和线性区域均显着排列，并且胶原蛋白束主要在线性区域接合和定向。这项研究增进了我们对皮肤生物力学的理解，并为未来皮肤组织的第一原理完整建模提供了输入。