Arbitrary 3D Organic Mixed Ionic‐Electronic Conductor Architectures via Self‐Fusion of PEDOT:PSS Microfibers

In this research, a first-of-its-kind fabricating strategy is reported that assembles arbitrary 3D organic mixed ionic-electronic conductor (OMIEC) architectures using poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) microfiber building blocks. This approach exploits a water-assisted self-fusion process, in which adhesion can be modulated as reversible (PSS-rich) or irreversible (PEDOT-rich) self-fusion depending on the post-treatment condition of building blocks. Phenomenological characterization and structural analyses reveal that hydration-induced swelling of hydrophilic PSS chains and crystalline π-π-stacked PEDOT domains govern interfacial bonding. Using PEDOT:PSS microfibers as modular units, structures ranging from 2D mesh electrodes to centimeter-scale free-standing 3D architectures are demonstrated. The resulting microfiber network structures are mechanically robust under bending and folding in aqueous environments and exhibit a high volumetric capacitance. Furthermore, hydration reduces the elastic modulus by ≈80%, enabling soft, conformal adhesion onto wet and irregular surfaces without additional adhesives. Finally, "cut-and-stick" PEDOT:PSS mesh electrodes are fabricated as a proof-of-concept and employed for recording in vivo cardiac activities from rodent hearts with minimal motion artifacts, outperforming conventional rigid platinum electrodes. This self-fusion strategy establishes a simple and scalable route for the first-time construction of arbitrary 3D OMIEC architectures, opening new opportunities for multifunctional OMIEC platforms in bioelectronics and energy-storage applications.