Université de Lyon, ECL - ENISE, LTDS UMR 5513, France; Laboratoires Clarins, Pontoise, France.
Université de Lyon, ECL - ENISE, LTDS UMR 5513, France.
J Mech Behav Biomed Mater. 2023 May;141:105798. doi: 10.1016/j.jmbbm.2023.105798. Epub 2023 Mar 24.
Human skin has a complex multilayer structure consisting of non-homogeneous, non-linear, viscoelastic and anisotropic materials subjected to in vivo natural pre-tension. This natural tension stems from networks of collagen and elastin fibers. The 3D organization of the collagen and elastin fibers underpins the multidirectional natural tensions in the skin volume while the state of the networks formed influences the surface topography of the skin. This topography depends on the area of the body and on the age of the person. Experiments reported in the literature have been performed ex vivo or on cadavers. By contrast, this work proposes the characterization of the anisotropic natural tension of the human skin in vivo. Experimental tests were performed on the forearms and thighs of 42 female volunteers representing two age groups [20 - 30] and [45-55] years old. Non-contact impact tests and skin-folding tests were conducted using devices developed at the LTDS (Lyon, France). The impact test generated a Rayleigh wave that spread in the skin. The speed of this wave was measured in 7 directions to study the anisotropy of the skin tension. The image of the skin relief at rest and during the skin folding test was reconstructed by optical confocal microscopy and provided the density of the skin lines printed on the outer surface of the skin. Skin folding test enables the clinician's manual procedure to be instrumented to identify tension lines i.e., Langer lines, for better healing during a surgical procedure. The main directions of natural skin tension deduced from the measured wave speed and the densities of skin lines were [40°-60°] for the forearm and [0°-20°] for the thigh, considering that the longitudinal axis of the body is situated at 90° and the transversal axis at 0°. This method shows the remarkable effect of age and body area on the mechanical behavior of human skin in vivo. The elastic properties and natural tension of the skin decrease with age. This decrease is greater in the directions orthogonal to the skin's tension lines, leading to the accentuation of the anisotropic behavior of the cutaneous tissue. The main direction of skin tension is highly dependent on the area of the body and is directed towards a preferred direction which corresponds to the main direction of skin tension.
人体皮肤具有复杂的多层次结构，由不均匀、非线性、粘弹性和各向异性材料组成，并受到体内天然预张力的作用。这种天然张力源于胶原和弹性纤维网络。胶原和弹性纤维的 3D 组织支撑着皮肤体积的多向天然张力，而网络的状态则影响着皮肤的表面形貌。这种形貌取决于身体的区域和人的年龄。文献中报道的实验是在离体或尸体上进行的。相比之下，这项工作提出了在体表征人体皮肤的各向异性天然张力。实验测试在 42 名女性志愿者的前臂和大腿上进行，志愿者代表两个年龄组[20-30]和[45-55]岁。使用在法国 Lyon 的 LTDS 开发的设备进行了非接触冲击测试和皮肤折叠测试。冲击测试产生了在皮肤中传播的瑞利波。测量了 7 个方向的波速以研究皮肤张力的各向异性。通过光学共焦显微镜重建了休息时和皮肤折叠测试时的皮肤起伏图像，并提供了打印在皮肤外表面的皮肤线的密度。皮肤折叠测试使临床医生的手动操作能够被仪器化，以识别张力线，即 Langer 线，从而在手术过程中更好地愈合。从测量的波速和皮肤线的密度推断出的天然皮肤张力的主要方向为前臂[40°-60°]和大腿[0°-20°]，假设身体的纵轴位于 90°，横轴位于 0°。该方法显示了年龄和身体区域对人体皮肤在体机械行为的显著影响。皮肤的弹性特性和天然张力随年龄的增长而降低。这种减少在垂直于皮肤张力线的方向上更大，导致皮肤组织的各向异性行为更加明显。皮肤张力的主要方向高度依赖于身体的区域，并指向一个优选的方向，该方向对应于皮肤张力的主要方向。
