Khatyr Fouad, Imberdis Claude, Vescovo Paul, Varchon Daniel, Lagarde Jean-Michel
Laboratoire de Mécanique Appliquée R. Chaléat, UMR 6604 CNRS IMFC 24, Besançon Cedex, France.
Skin Res Technol. 2004 May;10(2):96-103. doi: 10.1111/j.1600-0846.2004.00057.x.
The single-axis extension test is relatively little used to study the mechanical properties of human skin in vivo. A campaign of tests was carried out with an original, modern machine developed in our laboratory. It can perform extension or compression tests using servo-controlled position or force in different directions. The load can either be of the extension or monotonous compression type, creep or relaxation. The results obtained were used to develop a viscoelastic model. The elastic modulus calculated helps us to determine the main directions of anisotropy on the forearm.
We use a new in vivo single-axis extension machine (patent no. FR03/09220 application in progress). With it, we can carry out monotonous, creep and relaxation tests on the forearm. An associated finite elements model enables conversion to the intrinsic parameters of the skin under stress and strain from external stress applied in force and displacement. From the tests, we can propose a viscoelastic model and the identification of his parameters. We carried out tests in four directions with respect to the axis of the forearm of 63 people of different ages. The present report is limited to a brief presentation of the experimental set-up used, and a more complete presentation of the viscoelastic model and how it is defined and also the work on the anisotropy in the elastic domain.
The viscoelastic model proposed has only four intrinsic parameters: elasticity parameters E(e) and E(ve) and viscosity parameters epsilon(ve) and A. Skin being considered as orthotropic, we were able to determine the average main direction of 63 people, which is of 5.33+/-5.78 around the longitudinal axis of the arm. An average modulus E(1) (ave)=6.57E(5) (Pa) can be found in the direction close to the axis of the arm and E(2) (ave)=1.30E(5) (Pa) in the perpendicular direction and a G(12)=1.32E(5) (Pa) shear modulus.
The parameters obtained with the viscoelastic model are independent of the type of load, the same coefficients enable a correct representation in creep and relaxation tests. The main directions vary from one person to another, Young's modulus in these directions could be an indicator for dermatologists and cosmeticians.
单轴拉伸试验在体内研究人体皮肤力学性能方面的应用相对较少。我们使用实验室研发的一台新型现代机器进行了一系列试验。该机器能够在不同方向上通过伺服控制位置或力来进行拉伸或压缩试验。载荷可以是拉伸型或单调压缩型、蠕变或松弛型。所获得的结果用于建立一个粘弹性模型。计算得到的弹性模量有助于我们确定前臂各向异性的主要方向。
我们使用一台新型的体内单轴拉伸机器（专利号：FR03/09220，正在申请中）。利用它，我们可以在前臂上进行单调、蠕变和松弛试验。一个相关的有限元模型能够根据施加的力和位移所产生的外部应力，将其转换为皮肤在应力和应变作用下的固有参数。通过这些试验，我们可以提出一个粘弹性模型并确定其参数。我们针对63名不同年龄的人的前臂轴线在四个方向上进行了试验。本报告仅限于简要介绍所使用的实验装置，以及更完整地介绍粘弹性模型及其定义方式，还有弹性域内各向异性方面的研究工作。
所提出的粘弹性模型仅有四个固有参数：弹性参数E(e)和E(ve)以及粘性参数epsilon(ve)和A。考虑到皮肤为正交各向异性，我们能够确定63人的平均主方向，其围绕手臂纵轴为5.33±5.78。在靠近手臂轴线的方向上可测得平均模量E(1)(ave)=6.57E(5)(Pa)，在垂直方向上E(2)(ave)=1.30E(5)(Pa)，剪切模量G(12)=1.32E(5)(Pa)。
通过粘弹性模型获得的参数与载荷类型无关，相同的系数能够在蠕变和松弛试验中进行正确的表述。主方向因人而异，这些方向上的杨氏模量可能是皮肤科医生和美容师的一个指标。
