Although challenging, the preparation of pure conducting polymer (CP) hydrogels as conductive flexible networks for developing high-performance functional platforms is an outstanding alternative to conventional approaches, as for example those based on the cross-linking of insulating polymers with CP segments and the simple utilization of CPs as fillers of insulating hydrogel networks. In this work, we propose the employment of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to prepare conductive hydrogels by partially replacing the PSS dopant by alginate (Alg) chains, which is energetically favoured. The capacity of Alg chains to be electrostatically cross-linked by Ca²⁺ ions has allowed us to obtain hydrogels with good electrical percolation response and mechanical properties. Hydrogels were prepared in a very simple one-step process by adding CaCl₂ to different mixtures of PEDOT : PSS and alginic acid (1 : 3, 1 : 1 and 3 : 1). After structural, chemical and physical characterization, the 1 : 3 PEDOT/Alg hydrogel was moulded to fabricate stretchable touch-pressure sensor arrays, which exhibited fast response and good spatial resolution of the pressure distribution. In addition, the PEDOT/Alg hydrogel is self-healable which allowed us to prepare reusable pressure sensors (i.e. devices that can be reprocessed to be used in their original application) thanks to the reversibility of the noncovalent Ca²⁺ crosslinks. Reusable devices are different to reclaimed and recycled devices as these are no longer used for the same application because the materials lose their properties. With our hydrogels we are a step closer to a circular economy by allowing the reuse of electronic devices and reducing electronic waste worldwide. Moreover, the superior performance of the PEDOT/Alg hydrogel opens up its utilization as an efficient and flexible pressure sensor for wearable human-electronic interfaces, in which reusability would be an added value.

Field-driven direct assembly of nanoscale matter has impact in disparate fields of science. In microscale systems, such concept has been recently exploited to optimize propulsion in viscous fluids. Despite the great potential offered by miniaturization, using self-assembly to achieve transport at the nanoscale remains an elusive task. Here we show that a hybrid propeller, composed by a ferromagnetic nanorod and a paramagnetic microsphere, can be steered in a fluid in a variety of modes, from pusher to puller, when the pair is dynamically actuated by a simple oscillating magnetic field. We exploit this unique design to build more complex structures capable of carrying several colloidal cargos as microscopic trains that quickly disassemble at will under magnetic command. In addition, our prototype can be extended to smaller nanorods below the diffraction limit, but still dynamically reconfigurable by the applied magnetic field.