Enhancing Hydration Stability in PVA-Based Skin Phantoms For Biopotential Applications

Abstract The development of stable and biomimetic skin phantoms is crucial for reliable biopotential measurements in wearable sensor applications. Hydration instability disrupts electrical conductivity, leading to signal degradation and inconsistent impedance behavior, which limits the accuracy of bioelectrical measurements. Building on previous research, Dr. Goyal’s work established a controlled benchtop testing method for wearable electrodes, addressing the variability and unpredictability of human skin measurements [1,2]. The study introduced a two-layer skin phantom model, where the lower layer (polyvinyl alcohol cryogel, PVA-c) mimicked deeper tissues, while the upper layer simulated the stratum corneum using polydimethylsiloxane (PDMS) infused with carbon black and barium titanate. A critical finding was that the lower-layer PVA-c skin phantom experienced dehydration over time, causing impedance variability and reduced measurement accuracy, highlighting the need for enhanced hydration stabilization strategies. This study builds on these findings by focusing exclusively on the lower-layer PVA-c skin phantom, excluding the stratum corneum simulation, to directly optimize hydration stability and impedance consistency. PVA-c skin phantoms were fabricated using a boiling hotplate method with a 0.9% saline solution, avoiding chemical crosslinkers to ensure biocompatibility. To enhance moisture retention, hydrophilic additives—including aloe vera, trehalose, glycerin, and urea (0–5% w/w)—were applied, allowing controlled hydration levels to be sustained. Additionally, multiple freeze-thaw cycles (−20 °C for 12 hours, thaw at room temperature for 24 hours) were employed to refine polymer network density and stabilize hydration. To quantify hydration behavior, skin phantoms were evaluated for mass loss, impedance stability (1–1000 Hz), phase angle consistency, and permittivity using a precision weight balance, a tetrapolar electrode setup, and a corneometer. Stable hydration retention ensures consistent electrical conductivity, minimizing impedance variability in biosensor applications. The results demonstrate that glycerin and aloe vera-treated skin phantoms, along with a single freeze-thaw cycle, effectively optimize hydration stability while maintaining predictable impedance behavior across frequencies. This refinement in skin phantom fabrication enhances reproducibility in biopotential measurement models, supporting advancements in wearable sensor technology for continuous physiological monitoring.