Inspired by the work of Galvani in the 18th century, the field of bioelectronics leverages the optoelectronic properties of synthetic materials to interface with living systems. Bioelectronic applications require soft and biocompatible materials, with either ionic or electronic conductivity to detect or influence cellular processes. To meet these requirements, nanomaterials (conjugated polymers, carbon nanotubes, graphene) are typically dispersed within natural or synthetic biomaterials to afford conductive hydrogels. A significant challenge in the field remains the required high nanomaterial loadings to achieve measurable conductivity, but at such loadings, the conductive hydrogels become prohibitively rigid for bioelectronic applications. Unlike 2D thin-film applications that leverage the long-range ordering of nanomaterials such as conjugated polymers to achieve significant charge percolation, the 3D, complex, and tortuous structure of hydrogels prevents such material alignment, creating a barrier toward highly conductive soft hydrogels. To overcome this limitation, we developed PEDOT nanoparticles which behave as three-dimensional seeds for charge percolation throughout the hydrogel. By connecting these particles via in-situ polymerization of EDOT, we observed significant conductivity (&gt; 10 S cm-1) without deleterious hydrogel stiffening. PEDOT nanoparticles were incorporated within various synthetic and natural biomaterials at different loadings, with and without subsequent particle connection via in-situ polymerization, to understand the relationship between loading, conductivity, and mechanical properties. We found that through the combination of careful nanoparticle loading and in-situ polymerization, both conductive and soft hydrogels could be afforded. The scalability and conductivity of the PEDOT nanoparticles make them attractive fillers for conductive hydrogels and other bioelectronic applications.

PEDOT nanoparticles: A tool to enhance 3D charge percolation within conductive biomaterials

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