Intrinsically stretchable light-emitting diodes (LEDs) will be critical components in future stretchable electronics. However, limited research has been conducted on stretchable electroluminescent (EL) layers for LED devices. Blending conjugated polymers (CPs) with an elastomer has been a simple and effective method enabling widespread use of stretchable polymer semiconductors in stretchable field-effect transistors (FETs). In this study, we adopted the concept of blending elastomers into CPs for use in stretchable polymer LEDs (PLEDs). By blending light-emitting polymers prepared from polyphenylenevinylene (PPV) derivatives with thermoplastic polystyrene-block-polybutadiene-block-polystyrene (SBS) elastomers, a stretchable emission layer (EML) was fabricated, and its mechanical, electrical, and morphological properties were studied. The blended film was stretched up to 60% before vertical cracking occurred, and it maintained its pristine electrical properties. Finally, stretchable PLEDs were fabricated with the use of stretchable EMLs, and this showed that 50% of the maximum luminance was maintained upon stretching up to 60%.
For multifunctional wearable sensing systems, problems related to wireless and continuous communication and soft, noninvasive, and disposable functionality issues should be solved for precise physiological signal detection. To measure the critical transitions of pressure, temperature, and skin impedance when continuous pressure is applied on skin and tissue, we developed a sensor for decubitus ulcers using conventional analog circuitry for wireless and continuous communication in a disposable, breathable fabric-based multifunctional sensing system capable of conformal contact. By integrating the designed wireless communication module into a multifunctional sensor, we obtained sensing data that were sent sequentially and continuously to a customized mobile phone app. With a small-sized and lightweight module, our sensing system operated over 24 h with a coin-cell battery consuming minimum energy for intermittent sensing and transmission. We conducted a pilot test on healthy subjects to evaluate the adequate wireless operation of the multifunctional sensing system when applied to the body. By solving the aforementioned practical problems, including those related to wireless and continuous communication and soft, noninvasive, and disposable functionality issues, our fabric-based multifunctional decubitus ulcer sensor successfully measured applied pressure, skin temperature, and electrical skin impedance.
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