Soft Biomechanics & Tissue Engineering, Biomedical Engineering, Eindhoven University of Technology, Den Dolech 2, Gem-Z. 4.103, PO Box 513, 5600 MB Eindhoven, The Netherlands.
J Mech Behav Biomed Mater. 2013 Dec;28:462-70. doi: 10.1016/j.jmbbm.2013.01.024. Epub 2013 Feb 9.
Skin is a complex multi-layered tissue, with highly non-linear viscoelastic and anisotropic properties. Thus far, a few studies have been performed to directly measure the mechanical properties of three distinguished individual skin layers; epidermis, dermis and hypodermis. These studies however, suffer from several disadvantages such as skin damage due to separation, and disruption of the complex multi-layered composition. In addition, most studies are limited to linear shear measurements, i.e. measurements with small linear deformations (also called small amplitude oscillatory shear experiments), whereas in daily life skin can experience high strains, due to for example shaving or walking. To get around these disadvantages and to measure the non-linear mechanical (shear) behavior, we used through-plane human skin to measure large amplitude oscillatory shear (LAOS) deformation up to a strain amplitude of 0.1. LAOS deformation was combined with real-time image recording and subsequent digital image correlation and strain field analysis to determine skin layer deformations. Results demonstrated that deformation at large strains became highly non-linear by showing intra-cycle strain stiffening and inter-cycle shear thinning. Digital image correlation revealed that dynamic shear moduli gradually decreased from 8kPa at the superficial epidermal layer down to a stiffness of 2kPa in the dermis. From the results we can conclude that, from a mechanical point of view, skin should be considered as a complex composite with gradually varying shear properties rather than a three layered tissue.
皮肤是一种复杂的多层组织，具有高度非线性的黏弹性和各向异性特性。到目前为止，已经有一些研究旨在直接测量三个不同的皮肤层（表皮、真皮和皮下组织）的机械性能。然而，这些研究存在一些缺点，例如由于分离而导致的皮肤损伤，以及复杂的多层结构被破坏。此外，大多数研究仅限于线性剪切测量，即小线性变形（也称为小振幅振荡剪切实验）的测量，而在日常生活中，皮肤可能会经历高应变，例如刮胡子或走路。为了克服这些缺点并测量非线性力学（剪切）行为，我们使用平面内人皮肤来测量高达 0.1 应变幅度的大振幅振荡剪切（LAOS）变形。LAOS 变形与实时图像记录以及随后的数字图像相关和应变场分析相结合，以确定皮肤层的变形。结果表明，由于出现循环内应变硬化和循环间剪切变稀，大应变下的变形变得高度非线性。数字图像相关揭示了动态剪切模量逐渐从表皮层的 8kPa 下降到真皮层的 2kPa 的刚度。从结果可以得出结论，从力学角度来看，皮肤应被视为具有逐渐变化的剪切特性的复杂复合材料，而不是三层组织。
