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

## TL;DR

A new method creates 3D organic conductor structures using water-assisted fusion of microfibers, enabling soft, flexible electronics for bioapplications.

## Contribution

A first-of-its-kind strategy for building arbitrary 3D organic mixed ionic-electronic conductor architectures via self-fusion of PEDOT:PSS microfibers.

## Key findings

- Water-assisted self-fusion allows reversible or irreversible adhesion depending on post-treatment conditions.
- 3D microfiber networks are mechanically robust and exhibit high volumetric capacitance in wet environments.
- Soft, conformal adhesion to wet surfaces is achieved with minimal motion artifacts in cardiac activity recordings.

## Abstract

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.

A general fabricating strategy for arbitrary 3D organic mixed ionic‐electronic conductor architectures is reported using PEDOT:PSS microfiber building blocks. A water‐assisted self‐fusion process is successfully developed 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.