Rim Jee E, Pinsky Peter M, van Osdol William W
Department of Mechanical Engineering, Northwestern University, Evanston, IL 60628, USA.
J Biomech. 2008;41(4):788-96. doi: 10.1016/j.jbiomech.2007.11.011. Epub 2008 Feb 21.
The stratum corneum is the outermost layer of the skin, which acts as a barrier membrane against the penetration of molecules into and out of the body. It has a biphasic structure consisting of keratinized cells (corneocytes) that are embedded in a lipid matrix. The macroscopic transport properties of the stratum corneum are functions of its microstructure and the transport properties of the corneocytes and the lipid matrix, and are of considerable interest in the context of transdermal drug delivery and quantifying exposure to toxins, as well as for determining the relation of skin disorders to disruption of the stratum corneum barrier. Due to the complexity of the tissue and the difference in length scales involved in its microstructure, a direct analysis of the mass transport properties of the stratum corneum is not feasible. In this study, we undertake an approach where the macroscopic diffusion tensor of the stratum corneum is obtained through homogenization using the method of asymptotic expansions. The biphasic structure of the stratum corneum is fully accounted for by allowing the corneocytes to be permeable and considering the partitioning between the corneocytes and the lipid phases. By systematically exploring the effect of permeable corneocytes on the macroscopic transport properties of the stratum corneum, we show that solute properties such as lipophilicity and relative permeabilities in the two phases have large effects on its transdermal diffusion behavior.
角质层是皮肤的最外层，作为一种屏障膜，防止分子进出身体。它具有双相结构，由嵌入脂质基质中的角质化细胞（角质形成细胞）组成。角质层的宏观传输特性是其微观结构以及角质形成细胞和脂质基质传输特性的函数，在透皮给药、量化毒素暴露以及确定皮肤疾病与角质层屏障破坏之间的关系方面具有重要意义。由于组织的复杂性及其微观结构中涉及的长度尺度差异，直接分析角质层的质量传输特性是不可行的。在本研究中，我们采用一种方法，通过使用渐近展开法进行均匀化来获得角质层的宏观扩散张量。通过允许角质形成细胞具有渗透性并考虑角质形成细胞与脂质相之间的分配，充分考虑了角质层的双相结构。通过系统地探索可渗透角质形成细胞对角质层宏观传输特性的影响，我们表明溶质性质，如亲脂性和在两相中的相对渗透率，对其透皮扩散行为有很大影响。
