Abstract
The transepidermal water loss (TEWL) and the skin wettedness factor (SWF) are considered parts of a key perspective related to skincare. The former is used to determine the loss of water content from the stratum corneum (SC), while the latter is used to determine the human skin comfort level. Herein, we developed two novel approaches: (1) determination of the TEWL and the SWF based on a battery-free humidity sensor, and (2) the design of a battery-free smart skincare sensor device tag that can harvest energy from a near field communication (NFC)-enabled smartphone, making it a battery-free design approach. The designed skincare device tag has a diameter of 2.6 cm and could harvest energy (~3 V) from the NFC-enabled smartphone. A series of experimental tests involving the participation of eight and six subjects were conducted in vivo for the indoor and outdoor environments, respectively. During the experimental analysis, the skin moisture content level was measured at different times of the day using an android smartphone. The TEWL and SWF values were calculated based on these sensor readings. For the TEWL case: if the skin moisture is high, the TEWL is high, and if the skin moisture is low, the TEWL is low, ensuring that the skin moisture and the TEWL follow the same trend. Our smart skincare device is enclosed in a 3D flexible design print, and it is battery-free with an android application interface that is more convenient to carry outside than other commercially available battery-based devices.
Highlights
The human body’s skin can be divided into three depending layers: the hypodermis layer, the overlying dermis and the epidermis
Our smart skincare device is enclosed in a 3D flexible design print, and it is battery-free with an android application interface that is more convenient to carry outside than other commercially available battery-based devices
stratum corneum (SC) initiates the skin moisture; it is required to determine the level of skin hydration and other parameters related to its health
Summary
The human body’s skin can be divided into three depending layers: the hypodermis layer, the overlying dermis and the epidermis. Multimodal sensors with soft, ultrathin and skin-like formats were developed for monitoring the hydration level of the skin [2]. A wireless epidermal sensor based on passive inductive coupling was reported [3], where the analyzer was connected to a hand-wound copper primary coil, used to measure the hydration of the skin. An ultra-thin, tape free e-tattoo type sensor was designed, which could measure three features from the human skin, i.e., an electrocardiogram (ECG), the skin temperature and the skin hydration [4]. A machine-learning-based noninvasive solution has been purported that uses galvanic skin response (GSR) to detect the hydration level in the human body [5]. The measurements of the transepidermal water loss (TEWL) and the skin wettedness factor (SWF) have been given significant importance in many research areas like dermatology, pharmacology, clinical analysis and cosmetic science.
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