Division of Physical Chemistry, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-22100, Lund, Sweden.
Sci Rep. 2017 Nov 16;7(1):15712. doi: 10.1038/s41598-017-15921-5.
Hydration is a key aspect of the skin that influences its physical and mechanical properties. Here, we investigate the interplay between molecular and macroscopic properties of the outer skin layer - the stratum corneum (SC) and how this varies with hydration. It is shown that hydration leads to changes in the molecular arrangement of the peptides in the keratin filaments as well as dynamics of C-H bond reorientation of amino acids in the protruding terminals of keratin protein within the SC. The changes in molecular structure and dynamics occur at a threshold hydration corresponding to ca. 85% relative humidity (RH). The abrupt changes in SC molecular properties coincide with changes in SC macroscopic swelling properties as well as mechanical properties in the SC. The flexible terminals at the solid keratin filaments can be compared to flexible polymer brushes in colloidal systems, creating long-range repulsion and extensive swelling in water. We further show that the addition of urea to the SC at reduced RH leads to similar molecular and macroscopic responses as the increase in RH for SC without urea. The findings provide new molecular insights to deepen the understanding of how intermediate filament organization responds to changes in the surrounding environment.
水合作用是皮肤的一个关键方面，影响其物理和机械性能。在这里，我们研究了外皮肤层 - 角质层（SC）的分子和宏观性质之间的相互作用以及随水合作用的变化。结果表明，水合作用导致角蛋白丝中的肽的分子排列以及突出终端中的氨基酸的 C-H 键重取向动力学发生变化角质蛋白中的 SC。分子结构和动力学的变化发生在对应于约 85％相对湿度（RH）的阈值水合作用处。SC 分子性质的突然变化与 SC 宏观溶胀性质以及 SC 中的机械性质的变化相吻合。在固体角蛋白丝上的柔性末端可以与胶体系统中的柔性聚合物刷相比较，在水中产生长程排斥和广泛的溶胀。我们进一步表明，在低 RH 下向 SC 添加尿素会导致与没有尿素的 SC 中 RH 增加相似的分子和宏观响应。这些发现为深入了解中间丝组织如何响应周围环境的变化提供了新的分子见解。
