Wearable Smart Patches on Sustainable Chitosan With Reversible Microbial Growth-Inhibitory Properties

Chitosan, a polysaccharide upcycled from biowaste, has long promised sustainable, biocompatible, and antimicrobial films and devices, an appeal reinforced by its recent regulatory recognition, with several chitosan-based antibacterial dressings gaining clearance through the Food and Drug Administration's 510(k) pathway. Yet despite this momentum, its role in electronics has remained confined to single-device demonstrations. Here, we introduce a multilayer electronic platform built entirely on chitosan films, shifting its role from a mere material component to a system-level enabler. Using a low-cost, ambient-temperature, chemical-free cutter-based method, we directly pattern copper traces on flexible chitosan films at ∼750 µm resolution and stack them into soft multilayer circuits; an optional microfabrication step is employed solely for chips with sub-100 µm pad pitch. We mount off-the-shelf microelectronics—including amplifiers, light-emitting diodes (LEDs), photodetectors, integrated circuits (ICs), resistors, and capacitors—directly onto the patterned chitosan circuits, assembling complete functional systems such as wireless near field communication (NFC) and Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tags and fully operational Photoplethysmography (PPG) sensors, all seamlessly integrated within the chitosan platform. Notably, the UHF tag with an embedded temperature sensor demonstrates readings with better than 1°C accuracy, enabling practical applications in wearable monitoring, such as wound healing, as well as in food safety tracking. Beyond electronics, we uncover a crucial biological edge. Using a Green Fluorescent Protein (GFP) expressing E. coli strain, a transient loss of fluorescence and growth was observed during chitosan exposure, followed by full recovery upon film removal, with bacterial viability, plasmid stability, and normal metabolic function fully preserved. This unique, reversible, and controllable bacteriostatic effect underscores chitosan's potential as a safe, biocompatible substrate that, when integrated with electronics, enables the development of next-generation wearable, implantable, and environmental monitoring devices.