Reversible fiber fusion and fission: Materials that can cycle between states are of interest for actuators, soft robotics, or recoverable membranes for separations. Chang et al. show that a collection of graphene oxide fibers can fuse into a single stronger fiber upon immersion in a solvent, extraction, and drying under tension (see the Perspective by Cruz-Silva and Elías). The geometrical deformation of the fibers during drying and swelling plays an important role in the reversible cycles, with a large volume change between the dried and swelled fibers. Moreover, fibers made from polymers, glass, metal, or silk can be given these abilities when coated with a micron-sized layer of graphene oxide. Science , this issue p. 614 ; see also p. 573

The development of continuous conducting polymer fibres is essential for applications ranging from advanced fibrous devices to frontier fabric electronics. The use of continuous conducting polymer fibres requires a small diameter to maximize their electroactive surface, microstructural orientation, and mechanical strength. However, regularly used wet spinning techniques have rarely achieved this goal due primarily to the insufficient slenderization of rapidly solidified conducting polymer molecules in poor solvents. Here we report a good solvent exchange strategy to wet spin the ultrafine polyaniline fibres. The slow diffusion between good solvents distinctly decreases the viscosity of protofibers, which undergo an impressive drawing ratio. The continuously collected polyaniline fibres have a previously unattained diameter below 5 µm, high energy and charge storage capacities, and favorable mechanical performance. We demonstrated an ultrathin all-solid organic electrochemical transistor based on ultrafine polyaniline fibres, which operated as a tactile sensor detecting pressure and friction forces at different levels.

Chronic wound healing is a complex and long-standing problem, that has been a major and critical clinical concern around the world for years. Recent advances in digital wound dressings open new possibilities for solving the problem. Here, we report a battery-free, fully permeable, skin-adhesive, stretchable electronic wound bandage (iSAFE) for intelligent wound management. This electronic bandage exhibits superior properties in multiple features and can be conformally adhered to the skin wound. In addition, the iSAFE can accurately assess the wound conditions in-situ and thus adaptively perform localized drug release. The results from both in vitro and in vivo studies on animals prove the validity of wound monitoring, wound healing boosting and intelligent closed-loop wound management. Clinical trials on patients across age 18 to 95 with various types of wounds are performed. These results all indicate the unique and universality of the reported technology for wound monitoring and management.

Organic electrochemical transistors (OECTs) are emerging organic semiconducting devices intensively used in biological detection, environmental monitoring, biomimetic electronics, and computing circuits, due to the high transconductance, low working voltage, and exceptional biocompatibility. Most reported OECTs are based on planar structures built by two dimensional (2D) semiconducting materials, which have found great challenges of rigid architecture, complicated fabrication, and small-scale production. To improve overall performance and extend the use of OECTs into wearables, integralization, miniaturization, and intellectualization, researchers have made intensive efforts to use 1D conducting polymer fibres as active channel for building new breed of fibre-based OECTs, namely F-OECTs. Here we present the research progress of F-OECTs along three lines: working principles, evaluation methods, and applications. Covering from P-type polymer to N-type polymer, various kinds of conducting polymers have been processed into channel materials of F-OECTs through mainstream wet spinning methods. The prepared F-OECTs have been widely used in in vivo recording, in vitro detection, neuromorphic sensing, and logical circuits. To conclude this review, we summarized current challenges in terms of performance optimization and material innovation, further suggesting possible solutions. This review could provide guidance for understanding the working principles of F-OECTs, designing high-performance F-OECTs, and fabricating advanced electronics.