Wearable thermoelectric heatsinks designed by 3D-printed polyethylene-based composites

• 3D-printed PE-based composites developed for wearable thermal management. • Optimized printing parameters ensured high printability and structural integrity. • Demonstrated superior thermal conductivity and cooling performance. • Maintained flexibility suitable for wearable thermoelectric applications. • Proof-of-concept power generation from body–ambient temperature difference. Developing thermally conductive and flexible polymer composites holds significant promise for flexible thermoelectric (TE) devices, which are essential components of wearable self-powered electronics. This study introduces a thermally conductive, polyethylene-based composite for 3D-printed heatsink applications, aiming to replace traditional metal-based heatsinks in wearable TE systems. The composite incorporates polyethylene, expanded graphite, and phase change material (PCM) to achieve high mechanical flexibility, thermal conductivity, and latent heat storage capacity. The composition was optimized by adjusting the loadings of these components and evaluating their thermal and mechanical properties, and their 3D printability, using fused deposition modeling 3D printing. The optimized composite achieved a thermal conductivity of up to 6 W/(m K) while maintaining excellent printability and flexibility, which is essential for conformal integration in flexible systems. A wearable heatsink thermoelectric device 3D printed in this work comprises a flexible heatsink and a wrist strap embedded with TE modules designed to minimize thermal resistance between components. This configuration demonstrated an open-circuit voltage of 39.4 mV and a cooling effect of 4.5 °C under simulated human wear conditions. Additionally, the inclusion of PCM enabled reversible phase transitions for passive thermal regulation, making it a viable option for continuously powering wearable sensors and functional devices.