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One factor with great bearing on the electrochemical performance of conjugated polymers is the film morphology. A balance between crystalline and amorphous domains needs to be achieved for the polymer to have an optimal ionic‐electronic conductance. Herein, the morphological and electrochemical properties of poly(ethylenedioxythiophene) polymers functionalized with phosphonate groups separated by methylene and butylene alkyl spacers from the backbone are compared. Extending the spacer from methylene to butylene increases structural ordering in the solid state as revealed by grazing‐incidence wide‐angle X‐ray scattering. However, the ordered domains are only short range, suggestive of a paracrystalline morphology in which ordered regions are separated by amorphous regions. This has a negative impact on the intermolecular charge transport. The longer spacer appears to have impeded the uptake of hydrated counterions, seen by the increase in the ionization potential and energy requirement for electrochemical switching, as well as the decrease in the volumetric capacitance. These results elucidate the advantages of having the phosphonate pendant group close to the backbone, separated only by a methylene spacer. This synthetic design likely facilitates hydrated counterions to accumulate around the polar phosphonate groups, close to the doped backbone where they can easily compensate the charge carriers formed upon oxidation. [ABSTRACT FROM AUTHOR]

In the field of tissue engineering and regenerative medicine, developing cytocompatible 3D conductive scaffolds that mimic the native extracellular matrix is crucial for the engineering of excitable cells and tissues. In this study, a custom cryogenic extrusion 3D printer was developed, which afforded control over both the ink and printing surface temperatures. Using this approach, aqueous inks were printed into well-defined layers with high precision. A conductive hydrogel ink was developed from chitosan (CS) and edge-functionalised expanded graphene (EFXG). Different EFXG:CS ratios (between 60:40 and 80:20) were evaluated to determine both conductivity and printability. Using the novel customized cryogenic 3D printer, conductive structures of between 2 and 20 layers were produced, with feature sizes as small as 200 μm. The printed structures are mechanically robust and are electrically conducting. The highest Young's modulus and conductivity in a hydrated state were 2.6 MPa and ∼45 S/m, respectively. Cytocompatibility experiments reveal that the developed material supports NSC-34 mouse motor neuron-like cells in terms of viability, attachment, and proliferation. The distinctive mechanical and electrical properties of the 3D-printed structures would make them good candidates for the engineering of 3D-structured excitable cells. Moreover, this novel printing setup can be used to print other hydrogel-based inks with high precision and resolution., Competing Interests: No competing financial interests exist., (Copyright 2024, Mary Ann Liebert, Inc., publishers.)