Wearable Body Temperature Sensing with Autonomous Self-regulated Joule Heating and Passive Cooling for Healthcare Applications

Abstract

The positive temperature coefficient (PTC) effect observed in conductive polymer composites (CPCs) holds significant promise due to its wide materials selection and ability to offer enhanced sensitivity. However, traditional CPCs have relatively high PTC switching temperatures (typically above 100 °C) and are often unsuitable for bodily healthcare devices. This study introduces a novel approach leveraging the synergistic effect of an eco-friendly fatty acid, namely lauric acid (LA), with flexible styrene-ethylene-butylene-styrene (SEBS) thermoplastic elastomer (TPE) as a matrix and graphene nanoplatelets (GNPs) as a conductive filler. The composite film demonstrates exceptional temperature responsiveness at body-relevant temperatures (35–40 °C) with a PTC intensity reaching an unprecedented 4 orders of magnitude, set apart by its fine-tuning ability across a remarkable detecting temperature interval (Maximum temperature coefficient of resistance (TCR): 471.4% °C⁻¹). This advancement is facilitated through a carefully engineered morphology, wherein the distribution of LA significantly influences the conductive network's reformation within the composite, with the in-situ optical microscope used to reveal the reformation of the conductive network structure. The flexible composite demonstrates significant potential for body temperature sensing, self-regulating heating, and passive cooling, paving the way for future developments in eco-friendly, highly sensitive, and flexible sensors in wearable health monitoring and thermotherapy.