Recently, Ye Xinyuan and Li Leqi, two undergraduate students from Cohort 2022 of Chemical Engineering Program at Guangdong Technion - Israel Institute of Technology (GTIIT), published an academic article titled "Temporary Tattoo-Inspired, Skin-Adaptable Epidermal Electrode from an Ultrathin PU–PVA Film" in the TOP journal ACS Sensors as the first authors. Assoc. Prof. Wang Yan from GTIIT Chemical Engineering Program is the corresponding author of the article.

At the climbing class in GTIIT, Leqi encountered this challenging sport for the first time. As a beginner, she often experienced muscle soreness after climbing. Are the right muscles engaged? How to prevent sports injuries? These confusions became a source of inspiration for scientific exploration, culminating in a high-level paper inspired by a student's climbing experience. Much like the Italian poet Petrarch expressed in "The Ascent of Mount Ventoux"—"The experience of climbing the mountain is more valuable than the view from the summit"—it showcases the spirit of GTIIT students, who fear no challenges and strive to ascend the peaks of science.

Continuous high-fidelity physiological signal monitoring is essential in personalized healthcare, neurological rehabilitation, and brain research. Achieving such stable and precise bioelectrical recordings relies on the development of conformable, durable, and scalable skin-electrode interfaces. Conventional dry metal electrodes suffer from high impedance, motion artifacts, and poor comfort during long-term use, while wet gel electrodes, though highly adhesive and conductive, are bulky, dry out quickly, and lack breathability, limiting their utility in dynamic and extended monitoring scenarios. Additionally, many flexible bioelectronic platforms rely on costly materials (e.g., gold, graphene) and micro/nanofabrication processes, posing challenges for clinical translation and large-scale deployment.

It was her firsthand experience with climbing that inspired Leqi: Could a thin, breathable electrode, adhering to the skin like a temporary tattoo, be developed? By detecting muscle electrical signals (surface electromyography, sEMG), it could analyze the activation of different muscle groups in real time during climbing. This would help beginners and professional athletes alike understand their force application patterns, optimize training methods, and prevent injuries.

The idea resonated with the team, as the R&D process proved challenging. In the early stages, the stability of ultra-thin electrodes on the skin became the biggest challenge. "Although the signal performance was good, sweat or movement easily caused the electrodes to detach," said Xinyuan. "Tests with various materials and adhesives failed to yield an ideal solution."

A discovery in daily life provided a crucial clue. "While showering, I noticed that temporary tattoos adhered firmly to the skin after getting wet, without any adhesive. This 'water-activated adhesion' mechanism greatly intrigued me," shared Leqi. After further investigation, the team realized the phenomenon was essentially due to the rearrangement of hydrogen bonds activated by water. This offered a feasible path for developing a new type of skin electrode. Although hydrogen bonds are weaker than covalent bonds, they are flexible and reversible, forming more easily in moist environments. This finding prompted a significant shift in their research: the key to solving the adhesion issue lay not in pursuing bonding strength, but in the adaptability and synergy of the materials.

Based on this concept, the team developed a tattoo-inspired, skin-adaptable epidermal electrode composed of an ultrathin (5.2 μm) polyvinyl alcohol (PVA) film reinforced by electrospun polyurethane (PU) nanomesh. The PU–PVA hybrid electrode requires no external adhesive materials and can be rapidly applied to the skin surface using a simple NaCl/glycerol/water ternary hydration solution. It exhibits exceptional flexibility, breathability, and skin adhesion, and forms a hydrogen-bond-mediated interface with the skin upon hydration—eliminating the need for chemical adhesives or external activation. The fabrication process is rapid, low-cost, and compatible with scalable manufacturing.

5.2-μm-thick skin-adaptable PU-PVA tattoo

This "tattoo electrode" enables wireless acquisition of EMG, EEG, and ECG signals with high fidelity even during vigorous movement (e.g., climbing, push-up variations) and long-term wear (e.g., 24-hour ECG tracking). Its superior air and moisture permeability, mechanical durability, low skin–electrode impedance, and motion artifact suppression make it a highly promising platform for next-generation wearable electrophysiology and at-home healthcare monitoring.

PU-PVA tattoos for analyzing muscle recruitment dynamics during push-ups and climbing activities

Xinyuan noted that scientific research is not just about accumulating experiments but also about continuously reflecting on details and integrating theories. "It was our attention to factors like interface configuration and electrode water content that helped us establish a complete logic between materials and signals. This is one of my most valuable takeaways."

From a puzzle on the climbing wall to a breakthrough in the lab, this research originated from life and ultimately returns to life. Leqi said this is not only scientific exploration but also a fusion of passion and practice. "True innovation often emerges from those everyday moments we are willing to observe a little longer and ponder a little deeper."

Cao Xuanwen, a student from Cohort 2023, joined the research group as a freshman and is one of the co-authors of the paper. "Through this project, I learned how to design, execute, and summarize a complete research topic. The guidance from Prof. Wang Yan and senior students have made me more confident in independent research in the future."

"They were able to quickly grasp the core of the problem and propose practical and innovative solutions, successfully tackling several key technical difficulties." Dr. Wang Yan spoke highly of the students' independent thinking skills and creativity. "These achievements have not only advanced the field of wearable bioelectronics and flexible sensors, but also laid a strong foundation for their future academic careers."

ACS Sensors

ACS Sensors (JCR Q1, Top journal in the Chinese Academy of Sciences classification, IF = 9.1) is a flagship journal of the American Chemical Society dedicated to cutting-edge research in sensor science and technology. It offers a premier platform for reporting high-performance sensor systems spanning chemistry, materials science, biomedicine, environmental science, and engineering. The journal covers the full spectrum from fundamental sensing mechanisms to practical device integration, with particular focus on biosensing, electrochemical sensors, wearable electronics, neural interfaces, environmental monitoring, and imaging. Since its launch in 2016, ACS Sensors has become a leading journal in the field of wearable bioelectronics and high-precision electrophysiological monitoring, published by ACS Publications.

Text/Photos: Dr. Wang Yan's Team, GTIIT News & Public Affairs