Conductive, self-healable and reusable poly(3,4-ethylenedioxythiophene)-based hydrogels for highly sensitive pressure arrays
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 polymer 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, 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 its original application) thanks to the reversibility of the noncovalent Ca2+ crosslinks. Reusable devices are in opposition to reclaimed and recycled devices as they are no longer use for the same application because the materials lose their properties. With our hydrogel 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 PEDOT/Alg hydrogel opens up its utilization as efficient and flexible pressure sensors for wearable human-electronic interfaces, in which reusability would be an added value.