Multi‐Structural and Biodegradable Humidity Sensors with Enhanced Surface Hydrophilicity

Abstract The increasing environmental impact from electronic waste (e‐waste) has prompted research into sustainable materials for biodegradable and transient electronics. Although some progress has been achieved, further improvement in terms of performance and sustainability is needed. This study introduces a humidity sensor composed of biodegradable poly(D,L‐lactide‐co‐glycolide acid) (PDLG) in novel and multi‐structural morphologies. It highlights the role of the sensors’ microscopic structural features in their performance, particularly in humidity sensitivity, to maximize the retention and detection of water molecules. Techniques such as electrospinning and electrospray are used to achieve specific fiber and sphere morphologies. Oxygen plasma treatments tuned their surface hydrophilicity, enhancing moisture interaction. Physicochemical characterization revealed that plasma‐treated morphologies lost up to 93% of their weight after six weeks, demonstrating high sensor degradation. Functional tests showed that the sphere‐based sensor exhibited low hysteresis (0.19%), high sensitivity (3.9 × 10⁷ MΩ/% RH), excellent repeatability, and fast response time (0.43s) in the 60−95% RH range. Additionally, NaCl functionalization further improved detection sensitivity and extended the detection range down to 30% RH. The biodegradable nature of the PDLG sensors allows their natural decomposition into eco‐friendly by‐products, minimizing their environmental impact, and addressing the environmental challenges associated with e‐waste.