Thermally Degradable Inductors with Water-Resistant Metal Leaf/Oleogel Wires and Gelatin/Chitosan Hydrogel Films

Ingestible electronics monitor biometric information from outside the body. Making them with harmless or digestible materials will contribute to further reducing the burden on the patient's oral intake. Here, considering that the inductive part plays an important role in communications, we demonstrate a degradable inductor fabricated with harmless substances. Such a transient component must meet conflicting requirements for both operation and disassembly. Therefore, we integrated a substrate made of gelatin, a thermally degradable material, and a precision coil pattern made of edible gold or silver leaf. However, gelatin itself lost its initial shape easily due to quick sol-gel changes in physiological conditions. Thus, we managed the gelatin's thermal responsiveness by using a tangle of gelatin/chitosan gel networks and genipin, an organic cross-linking agent, and gained insights into the criteria for developing transient devices with thermo-degradability. In addition, to compensate for the lack of water resistance and low conductivity of thin metal foils, we propose a laminated structure with oleogel (beeswax/olive oil). LCR resonance circuits, by connecting a commercial capacitor to the coil, worked wirelessly in the megahertz band and gradually degraded in a warm-water environment. The presented organic electronics will contribute to the future development of transient wireless communications for implantable and ingestible medical devices or environmental sensors with natural and harmless ingredients.