From Food to Power: Hydrogel Thermoelectrics for Ingestible Electronics

ABSTRACT Edible electronics present new opportunities for food‐integrated sensing and monitoring, yet powering such devices safely and effectively remains a major challenge. Here, we introduce a fully edible thermoelectric–electrochromic platform capable of converting heat from food into a visually perceptible color change, such that this platform can be used for real‐time temperature monitoring. TEGs are fabricated from vanillin‐crosslinked chitosan and alginate hydrogels functionalized with potassium chloride used as an electrolyte. Positively charged chitosan acts as a p‐type hydrogel, whereas the negatively charged alginate serves as an n‐type hydrogel. To increase the voltage of the edible device, we connect multiple p‐ and n‐type hydrogels in series. The resulting TEGs successfully drive anthocyanin‐functionalized, gelatin‐based electrochromic displays that are purple at room temperature and blue when the temperature exceeds 45°C. Transient heat sources, such as a freshly heated cake, are sufficient to trigger the color change. This work demonstrates that fully edible materials can be engineered to harvest thermal energy and convert it into a visible signal. The platform establishes a foundation for safe, biodegradable, and ingestible devices for on‐food monitoring, transient electronics, and food safety applications, offering a new approach to integrate sensing and display functionalities in edible systems.