Stretchable composite conductive fibers (SCCFs) exhibit remarkable conductivity, stretchability, breathability, and biocompatibility, making them ideal candidates for wearable electronics and bioelectronics. The exploitation of SCCFs in electronic devices requires a careful balance of many aspects, including material selection and process methodologies, to address the complex challenges associated with their electrical and mechanical properties. In this review, we elucidate the conductive mechanism of SCCFs and summarize strategies for integrating various conductors with stretchable fibers, emphasizing the primary challenges in fabricating highly conductive fibers. Furthermore, we explore the multifaceted applications of SCCFs-based frameworks in wearable electronic devices. This review aims to emphasize the significance of SCCFs and offers insights into their conductive mechanisms, material selection, manufacturing technologies, and performance improvement. Hopefully, it can guide the innovative development of SCCFs and broaden their application potential.

The incorporation of waterborne polyurethane (WPU) into bacterial cellulose (BC) fibers significantly improved the tensile strength of the resulting WPU/BC composite film, achieving an enhancement of 19.4 times. The formation of hydrogen bonds between WPU and BC effectively eliminates cavities within the BC matrix, achieving significant plasticization and toughening. Compared with the pure BC film (WPU/BC-0), the elastic modulus of the WPU/BC-5 composite film is reduced by 97.5%, and surface hardness is decreased by 96.9%. When integrated with a flexible EGaIn electrode, the wearable composite film demonstrated exceptional potential in flexible electronics, reliably enabling point-of-care detection of human electrocardiograph (ECG) signals. This WPU-regulated BC approach provides a promising alternative for fabricating flexible and durable substrates suitable for wearable device applications.

Flexible electrothermal heaters have attracted abundant attention in recent years due to their wide applications, but their preparation with high efficiency remains a challenge. Here in this work, a highly stable and bending-tolerant flexible heater was fabricated with graphite nanosheets and cellulose fibers through a scalable papermaking procedure. Its electrothermal property can be enhanced by a hot-pressing treatment and introduction of cationic polyacrylamide (CPAM) during the papermaking protocol. The flexible heater may quickly reach its maximum temperature of 239.8 °C in around 1 min at a voltage of 9 V. The power density was up to 375.3 °C cm² w⁻¹. It appeared to have a high tolerance for bending deformation with various curvatures, and the temperature remained stable even under 100 bending with frequency of around 0.17 Hz. Over 100 alternatively heating and cooling cycles, it worked stably as well. It was proved to be used as wearable heating equipment, soft heaters, and aircraft deicing devices, suggesting its great prospect in the field of heat management.