The bioimpedances of tissues beyond the stratum corneum, which is the outermost layer of skin, contain crucial clinical information. Nevertheless, bioimpedance measurements of both the viable skin and the adipose tissue are not widely used, mainly because of the complex multilayered skin structure and the electrically insulating nature of the stratum corneum. Here, a theoretical framework is established for analyzing the impedances of multilayered tissues and, in particular, of skin. Then, strategies are determined for the system-level design of electrodes and electronics, which minimize 4-wire (or tetrapolar) measurement errors even in the presence of a top insulating tissue, thus enabling non-invasive characterizations of tissues beyond the stratum corneum. As an example, non-invasive measurements of bioimpedances of living tissues are demonstrated in the presence of parasitic impedances which are much (e.g., up to 350 times) higher than the bioimpedances of the living tissues beyond the stratum corneum, independently on extreme variations of the barrier (tape stripping) or of the skin–electrode contact impedances (sweat). The results can advance the development of bioimpedance systems for the characterization of viable skin and adipose tissues in several applications, including transdermal drug delivery and the assessment of skin cancer, obesity, dehydration, type 2 diabetes mellitus, cardiovascular risk, and multipotent adult stem cells.

中文翻译：

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皮肤生物阻抗基础知识

角质层（皮肤的最外层）以外的组织的生物阻抗包含重要的临床信息。然而，活体皮肤和脂肪组织的生物阻抗测量并未广泛使用，这主要是因为复杂的多层皮肤结构和角质层的电绝缘性质。在这里，建立了一个理论框架来分析多层组织，特别是皮肤的阻抗。然后，确定电极和电子设备的系统级设计策略，即使在存在顶部绝缘组织的情况下，也能最大限度地减少 4 线（或四极）测量误差，从而能够对角质层以外的组织进行非侵入性表征。作为一个例子，活体组织生物阻抗的非侵入性测量在存在寄生阻抗的情况下被证明，该寄生阻抗比角质层之外的活体组织的生物阻抗高得多（例如，高达350倍），独立于屏障（胶带剥离）或皮肤电极接触阻抗（汗液）。这些结果可以促进生物阻抗系统的开发，用于在多种应用中表征活皮肤和脂肪组织，包括透皮药物输送和皮肤癌、肥胖、脱水、2型糖尿病、心血管风险和多能成体干细胞的评估。