There is an increasing need to develop conducting hydrogels for bioelectronic applications. In particular, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hydrogels have become a research hotspot due to their excellent biocompatibility and stability. However, injectable PEDOT:PSS hydrogels have been rarely reported. Such syringe‐injectable hydrogels are highly desirable for minimally invasive biomedical therapeutics. Here, an approach is demonstrated to develop injectable PEDOT:PSS hydrogels by taking advantage of the room‐temperature gelation property of PEDOT:PSS. These PEDOT:PSS hydrogels form spontaneously after syringe injection of the PEDOT:PSS suspension into the desired location, without the need of any additional treatments. A facile strategy is also presented for large‐scale production of injectable PEDOT:PSS hydrogel fibers at room temperature. Finally, it is demonstrated that these room‐temperature‐formed PEDOT:PSS hydrogels (RT‐PEDOT:PSS hydrogel) and hydrogel fibers can be used for the development of soft and self‐healable hydrogel bioelectronic devices.

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Gelatin methacryloyl (GelMA) is a widely used hydrogel with skin-derived gelatin acting as the main constituent. However, GelMA has not been used in the development of wearable biosensors, which are emerging devices that enable personalized healthcare monitoring. This work highlights the potential of GelMA for wearable biosensing applications by demonstrating a fully solution-processable and transparent capacitive tactile sensor with microstructured GelMA as the core dielectric layer. A robust chemical bonding and a reliable encapsulation approach are introduced to overcome detachment and water-evaporation issues in hydrogel biosensors. The resultant GelMA tactile sensor shows a highpressure sensitivity of 0.19 kPa −1 and one order of magnitude lower limit of detection (0.1 Pa) compared to previous hydrogel pressure sensors owing to its excellent mechanical and electrical properties (dielectric constant). Furthermore, it shows durability up to 3000 test cycles because of tough chemical bonding, and long-term stability of 3 days due to the inclusion of an encapsulation layer, which prevents water evaporation (80% water content). Successful monitoring of various human physiological and motion signals demonstrates the potential of these GelMA tactile sensors for wearable biosensing applications.