Self‐Adhesive and Ultra‐Conformable, Sub‐300 nm Dry Thin‐Film Electrodes for Surface Monitoring of Biopotentials

• Published in: Advanced functional materials Vol. 28; no. 36
• Main Authors: Nawrocki, Robert A., Jin, Hanbit, Lee, Sunghoon, Yokota, Tomoyuki, Sekino, Masaki, Someya, Takao
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 05.09.2018
• Subjects: Adhesives; bioelectronics; biopotentials; Elastomers; Electrodes; EMG/ECG; e‐skin; Materials science; Mathematical analysis; Monitoring; Sensors; Stiffness; ultraflexible electronics; Weight reduction
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201803279

Accurate and unobtrusive monitoring of surface biopotentials is of paramount importance for physiological studies and wearable healthcare applications. Thin, light‐weight, and conformal bioelectrodes are highly desirable for biopotential monitoring. This report demonstrates the fabrication of sub‐300 nm thin, dry electrodes that are self‐adhesive and conformable to complex 3D biological surfaces and thus capable of excellent quality of biopotential (surface electromyogram and surface electrocardiogram) recordings. Measurements reveal single‐day stability of up to 10 h. In addition, the bending stiffness of the sensor is calculated to be ≈0.33 pN m2, which is comparable to stratum corneum, the uppermost layer of human skin, and this stiffness is over two orders of magnitude lower than the bending stiffness of a 3.0 µm thin sensor. Laminated on a prestretched elastomer, when relaxed, the sensor forms wrinkles with a period and amplitude equal to 17 and 4 µm, respectively, which these values agree with theoretical calculations. Finally, with skin vibrations of up to ≈15 µm, the sensor exhibits motion artifact‐less monitoring of surface biopotentials, in contrast to a wet adhesive electrode that shows much greater influence. Sub‐300 nm dry, thin film electrodes are shown to be self‐adhesive and ultra‐conformal to complex 3D structures, including human skin. They exhibit excellent biopotential (surface electromyogram/surface electrocardiogram) recording capabilities, and long‐term stability, while being immune to motion artifacts. Due to their thinness, their bending stiffness is comparable to the stratum corneum, the outer layer of human skin.