SFI Centre for Research Training in Foundations of Data Science, University College Dublin, Belfield, Dublin 4, Ireland.
School of Mechanical and Materials Engineering, University College Dublin, Belfield, Dublin 4, Ireland.
Ann Biomed Eng. 2023 Aug;51(8):1781-1794. doi: 10.1007/s10439-023-03185-2. Epub 2023 Apr 6.
In vivo skin exhibits viscoelastic, hyper-elastic and non-linear characteristics. It is under a constant state of non-equibiaxial tension in its natural configuration and is reinforced with oriented collagen fibers, which gives rise to anisotropic behaviour. Understanding the complex mechanical behaviour of skin has relevance across many sectors including pharmaceuticals, cosmetics and surgery. However, there is a dearth of quality data characterizing the anisotropy of human skin in vivo. The data available in the literature is usually confined to limited population groups and/or limited angular resolution. Here, we used the speed of elastic waves travelling through the skin to obtain measurements from 78 volunteers ranging in age from 3 to 93 years old. Using a Bayesian framework allowed us to analyse the effect that age, gender and level of skin tension have on the skin anisotropy and stiffness. First, we propose a new measurement of anisotropy based on the eccentricity of angular data and conclude that it is a more robust measurement when compared to the classic "anisotropic ratio". Our analysis then concluded that in vivo skin anisotropy increases logarithmically with age, while the skin stiffness increases linearly along the direction of Langer Lines. We also concluded that the gender does not significantly affect the level of skin anisotropy, but it does affect the overall stiffness, with males having stiffer skin on average. Finally, we found that the level of skin tension significantly affects both the anisotropy and stiffness measurements employed here. This indicates that elastic wave measurements may have promising applications in the determination of in vivo skin tension. In contrast to earlier studies, these results represent a comprehensive assessment of the variation of skin anisotropy with age and gender using a sizeable dataset and robust modern statistical analysis. This data has implications for the planning of surgical procedures and questions the adoption of universal cosmetic surgery practices for very young or elderly patients.
体内皮肤表现出粘弹性、超弹性和非线性特性。在其自然结构中，它处于恒定的非双向张力状态，并由定向胶原纤维增强，这导致各向异性行为。理解皮肤的复杂力学行为在许多领域都具有相关性，包括制药、化妆品和外科手术。然而，关于体内皮肤各向异性的高质量数据非常匮乏。文献中可用的数据通常仅限于有限的人群组和/或有限的角分辨率。在这里，我们使用弹性波在皮肤中传播的速度从 78 名志愿者中获得测量结果，志愿者的年龄从 3 岁到 93 岁不等。使用贝叶斯框架允许我们分析年龄、性别和皮肤张力水平对皮肤各向异性和刚度的影响。首先，我们提出了一种基于角数据偏心率的新的各向异性测量方法，并得出结论，与经典的“各向异性比”相比，它是一种更稳健的测量方法。我们的分析然后得出结论，体内皮肤各向异性随年龄呈对数增长，而皮肤刚度沿朗格线方向呈线性增长。我们还得出结论，性别不会显著影响皮肤各向异性的水平，但会影响整体刚度，男性的皮肤平均更硬。最后，我们发现皮肤张力水平显著影响这里使用的各向异性和刚度测量。这表明弹性波测量在确定体内皮肤张力方面可能具有广阔的应用前景。与早期研究相比，这些结果代表了使用大量数据集和稳健的现代统计分析对皮肤各向异性随年龄和性别变化的全面评估。这些数据对外科手术计划有影响，并对非常年轻或年老患者采用通用美容手术实践提出了质疑。
