like poly (3,4-ethylenedioxythiophene):poly( styrene sulfonate) (PEDOT:PSS), stand out for this application due to their enhanced charge storage and coupled transport properties. [2][3][4] These functional materials are commonly used for recording physiological signals, assessing biochemical information, and electrical stimulation/ modulation. Ionic-electronic conductive hydrogels are another important family of soft conductors that have been broadly explored in healthcare technologies due to their similarities to biological tissues and tunability in terms of electronic, mechanical, and chemical properties. [5] In particular, natural biopolymers-based hydrogels are attractive platforms for wearable devices as they combine inherent renewable, non-toxic features, biocompatibility, and biodegradability. [6,7] Several examples of natural biopolymers have been reported as promising building blocks in stretchable devices, including cellulose, [8][9][10] chitosan, [11][12][13] alginate, [14][15][16] silk fibroin, [17,18] and gelatin. [19][20][21] Unfortunately, these conductive hydrogels fail in long-lasting signals recording due to the continuous water evaporation in open-air sensors and bioelectrodes. At this point, ionic liquid Eutectogels are a new class of soft ion conductive materials that are attracting attention as an alternative to conventional hydrogels and costly ionic liquid gels to build wearable sensors and bioelectrodes. Herein, the first example of mixed ionic and electronic conductive eutectogels showing high adhesion, flexibility, nonvolatility, and reversible low-temperature gel transition for 3D printing manufacturing is reporting. The eutectogels consist of choline chloride/glycerol deep eutectic solvent, poly(3,4-ethylenedioxythiophene): lignin sulfonate, and gelatin as the biocompatible polymer matrix. These soft materials are flexible and stretchable, show high ionic and electronic conductivities of 7.3 and 8.7 mS cm −1 , respectively, and have high adhesion energy. Due to this unique combination of properties, they could be applied as strain sensors to precisely detect physical movements. Furthermore, these soft mixed ionic electronic conductors possess excellent capacity as conformal electrodes to record epidermal physiological signals, such as electrocardiograms and electromyograms, over a long time.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admt.202101680.

Conducting polymers (CPs) have been attracting great attention in the development of (bio)electronic devices. Most of the current devices are rigid two-dimensional systems and possess uncontrollable geometries and architectures that lead to poor mechanical properties presenting ion/electronic diffusion limitations. The goal of the article is to provide an overview about the additive manufacturing (AM) of conducting polymers, which is of paramount importance for the design of future wearable three-dimensional (3D) (bio)electronic devices. Among different 3D printing AM techniques, inkjet, extrusion, electrohydrodynamic, and light-based printing have been mainly used. This review article collects examples of 3D printing of conducting polymers such as poly(3,4-ethylene-dioxythiophene), polypyrrole, and polyaniline. It also shows examples of AM of these polymers combined with other polymers and/or conducting fillers such as carbon nanotubes, graphene, and silver nanowires. Afterward, the foremost applications of CPs processed by 3D printing techniques in the biomedical and energy fields, that is, wearable electronics, sensors, soft robotics for human motion, or health monitoring devices, among others, will be discussed.

3D conductive materials such as polymers and hydrogels that interface between biology and electronics are actively being researched for the fabrication of bioelectronic devices. In this work, short-time (5 s) photopolymerizable conductive inks based on poly(3,4-ethylenedioxythiophene) (PEDOT):polystyrene sulfonate (PSS) dispersed in an aqueous matrix formed by a vinyl resin, poly(ethylene glycol) diacrylate (PEGDA) with different molecular weights ( M n = 250, 575, and 700 Da), ethylene glycol (EG), and a photoinitiator have been optimized. These inks can be processed by Digital Light 3D Printing (DLP) leading to flexible and shape-defined conductive hydrogels and dry conductive PEDOTs, whose printability resolution increases with PEGDA molecular weight. Besides, the printed conductive PEDOT-based hydrogels are able to swell in water, exhibiting soft mechanical properties (Young’s modulus of ∼3 MPa) similar to those of skin tissues and good conductivity values (10 –2 S cm –1 ) for biosensing. Finally, the printed conductive hydrogels were tested as bioelectrodes for human electrocardiography (ECG) and electromyography (EMG) recordings, showing a long-term activity, up to 2 weeks, and enhanced detection signals compared to commercial Ag/AgCl medical electrodes for health monitoring.