Leaf-Based Ultrasensitive Electronic Skins for Wearable Human Motion Monitoring

Nonbiodegradable components, such as synthetic polymers, have been widely used in the fabrication of flexible sensors and electronic skins (e-skins), resulting in the generation of electronic waste and toxic by-products. To overcome this issue, a wide range of biodegradable natural biopolymers and synthetic polymers have been employed to fabricate flexible sensors and wearable electronics. However, most current biodegradable e-skins demonstrate limitations such as low sensitivity, poor electrical conductivity, limited breathability, and low stability. Inspired by nature, to address these limitations, we introduce a series of highly breathable and ultrasensitive e-skin based on the coating of leaf skeletons with electrically conductive nanomaterials including, oxidized single-walled carbon nanotube (Ox-SWCNT), silver nanowire (AgNW), and carboxylated multi-walled carbon nanotubes (COOH-MWCNTs). We propose various e-skins based on different transduction strategies including capacitive and piezoresistive mechanisms. Our disposable capacitive e-skin exhibits a wide sensing range (0.01–97 kPa), high sensitivity (0.86 ± 0.16 kPa^-1), low limit of detection (~10 Pa), linearity for low- and high-pressure regimes, flexibility, breathability, high stability (3000 cycles), and biodegradability. In addition, the multilayered disposable e-skin based on piezoresistive transduction exhibits a remarkable performance including high sensitivity (19.75 ± 1.5 kPa⁻¹), wide sensing range (<42 kPa), ultralow limit of detection (~0.27 Pa), linearity for low- and high-pressure regimes, high flexibility, high stability (3000 cycles), low weight, ultrahigh breathability, and biodegradability. The developed leaf-based e-skins demonstrate outstanding sensing performance in human-motion monitoring by detecting various motions such as subtle and vigorous flexions, airflow, and vocal-cord vibrations. The proposed capacitive and piezoresistive e-skins are promising platforms for the development of various low-cost, biocompatible, biodegradable, and point-of-care e-skins for a wide range of subtle and vigorous pressure-monitoring applications including human–machine interfaces, robotics, prosthesis, and wearable electronics.