Melanin-inspired conductive thin films for multimodal-sensing wearable on-skin electronics

Electronic skins (e-skins), composed of various flexible sensors, mimic the sensing functions of human skin aiming for both healthcare monitoring and prosthetics development applications. So far different multi -component e-skin devices aimed to fulfill different requirements (biocompatibility, skin adhesion, flexibility, conductivity, sensitivity towards biological stimuli and stretchability) have been reported. However, the obtaining of such devices combining all the above requirements within a single material that simplifies not only cost but specially functioning still remains a challenge. For this, catechol-based materials have attracted special attention due to their adhesive properties, compatibility and melanin-like electrical conduction. In this work, 2,3,6,7,10,11 - hexahydroxy triphenylene (HHTP) was used as catechol moiety in a typical melanin-like poly-merization, resulting in a free-standing melanin-inspired film (MN-film). The obtained MN-film showcased good conductivities with dual charge carriers (electrons and ions) under different environments, i.e. pure water and buffers simulating sweat. Large biocompatibility, adhesion and conformability to skin were obtained as well, allowing to implement the film in wearable electronic on-skin devices on porcine skin. Measurements in wearable devices indicated large sensitivity towards different stimuli (strain, motion and temperature) under sweat-like conditions.