Querrey-Simpson Institute for Bioelectronics, Northwestern University, Evanston, IL 60208.
School of Electrical Engineering, Korea Advanced Institute of Science and Technology, 34141 Daejeon, Republic of Korea.
Proc Natl Acad Sci U S A. 2021 Feb 2;118(5). doi: 10.1073/pnas.2020398118.
Precise, quantitative measurements of the hydration status of skin can yield important insights into dermatological health and skin structure and function, with additional relevance to essential processes of thermoregulation and other features of basic physiology. Existing tools for determining skin water content exploit surrogate electrical assessments performed with bulky, rigid, and expensive instruments that are difficult to use in a repeatable manner. Recent alternatives exploit thermal measurements using soft wireless devices that adhere gently and noninvasively to the surface of the skin, but with limited operating range (∼1 cm) and high sensitivity to subtle environmental fluctuations. This paper introduces a set of ideas and technologies that overcome these drawbacks to enable high-speed, robust, long-range automated measurements of thermal transport properties via a miniaturized, multisensor module controlled by a long-range (∼10 m) Bluetooth Low Energy system on a chip, with a graphical user interface to standard smartphones. Soft contact to the surface of the skin, with almost zero user burden, yields recordings that can be quantitatively connected to hydration levels of both the epidermis and dermis, using computational modeling techniques, with high levels of repeatability and insensitivity to ambient fluctuations in temperature. Systematic studies of polymers in layered configurations similar to those of human skin, of porcine skin with known levels of hydration, and of human subjects with benchmarks against clinical devices validate the measurement approach and associated sensor hardware. The results support capabilities in characterizing skin barrier function, assessing severity of skin diseases, and evaluating cosmetic and medication efficacy, for use in the clinic or in the home.
精确、定量地测量皮肤的水合状态，可以深入了解皮肤的健康状况和皮肤结构与功能，这对体温调节等基本生理过程和其他特征也具有重要意义。现有的皮肤水分含量测定工具利用笨重、刚性和昂贵的仪器进行替代的电评估，这些仪器难以重复使用。最近的替代方法则利用柔软的无线设备进行热测量，这些设备可以轻柔、非侵入性地贴合皮肤表面，但操作范围有限（约 1 厘米），对细微的环境波动非常敏感。本文介绍了一系列理念和技术，克服了这些缺点，可以通过由远距离（约 10 米）蓝牙低能耗系统控制的、带有小型多传感器模块的设备，实现热传输特性的高速、稳健、远程自动化测量，同时配备标准智能手机的图形用户界面。与皮肤表面的软接触，几乎没有用户负担，可以通过计算建模技术，将记录与表皮和真皮的水合水平定量关联起来，具有高水平的可重复性和对环境温度波动的不敏感性。对类似于人体皮肤的层状结构的聚合物、具有已知水合水平的猪皮，以及与临床设备对照的人体研究的系统研究，验证了测量方法和相关传感器硬件。这些结果支持了皮肤屏障功能的特征描述、皮肤疾病严重程度的评估以及化妆品和药物疗效的评估等功能，可用于临床或家庭环境。
