Skin hydration dynamics investigated by electrical impedance techniques in vivo and in vitro

Abstract

Skin is easily accessible for transdermal drug delivery and also attractive for biomarker sampling. These applications are strongly influenced by hydration where elevated hydration generally leads to increased skin permeability. Thus, favorable transdermal delivery and extraction conditions can be easily obtained by exploiting elevated skin hydration. Here, we provide a detailed in vivo and in vitro investigation of the skin hydration dynamics using three techniques based on electrical impedance spectroscopy. Good correlation between in vivo and in vitro results is demonstrated, which implies that simple but realistic in vitro models can be used for further studies related to skin hydration (e.g., cosmetic testing). Importantly, the results show that hydration proceeds in two stages. Firstly, hydration between 5 and 10 min results in a drastic skin impedance change, which is interpreted as filling of superficial voids in skin with conducting electrolyte solution. Secondly, a subtle impedance change is observed over time, which is interpreted as leveling of the water gradient across skin leading to structural relaxation/changes of the macromolecular skin barrier components. With respect to transdermal drug delivery and extraction of biomarkers; 1 h of hydration is suggested to result in beneficial and stable conditions in terms of high skin permeability and extraction efficiency.

Micropore Closure Rates following Microneedle Application at Various Anatomical Sites in Healthy Human Subjects

“…The results in our study showed that baseline skin impedance at the abdomen was significantly higher than at the upper arm across all subjects, and within the Latino and black self-identified racial/ethnic groups. This higher impedance at the abdomen may be due to the lower skin hydration observed at the abdomen when compared to the upper arm and volar forearm, as studies have shown that increased skin hydration may lead to increased skin permeability and consequently a decrease in skin membrane electrical resistance [26][27][28].…”

Hydrogels and Cubic Liquid Crystals for Non-Invasive Sampling of Low-Molecular-Weight Biomarkers—An Explorative In Vivo Study

“…After 2 h, the Finn Chambers were removed, and the skin surface was gently wiped with a sterile cotton tissue. The reason for employing 2 h as the sampling time was to enable sufficient skin hydration [40], as well as adequate time for extraction of analytes, such as Trp and Kyn [33], while at the same time we were able to avoid an extensively long sampling time for practical reasons. Preliminary in vivo studies performed with CHI, where the sampling time was varied between 0.5 h, 2 h, 4 h, and 8 h, indicated that the amounts increased linearly over time.…”

Modeling Stratum Corneum Swelling for the Optimization of Electrode-Based Skin Hydration Sensors

“…This work will enable better electrode designs and will be beneficial to several applications. In the fields of cosmetics and drug delivery, it will allow to improve upon current methods used to investigate and characterize SC hydration [29,30]. For example, it has been experimentally reported that some types of electrodes exhibit better performances when measuring either very hydrated or very dry skin, without providing theoretical explanations for such results [31,32].…”