Researchers at Washington University in St. Louis have developed a new method to create spherical microparticles from the conducting polymer PEDOT:PSS. These microparticles enable the formation of injectable, flexible granular hydrogels for bioelectronic applications.
Conventional bioelectronic devices are often rigid, made of metal, silicon, or glass, and poorly matched to the soft, dynamic properties of biological tissues. These mismatches can lead to foreign body responses and compromise signal fidelity.
Hydrogels are a softer, more tissue-like alternative.
While many conducting hydrogels exist, most are non-microporous and fixed in shape, limiting cellular integration and adaptability.
Granular hydrogels, formed from densely packed microgel particles, have greater flexibility, injectability, and microporosity; however, their use in conductive systems has been largely unexplored until now.
Simpler Fabrication With Tunable Properties
To address scalability challenges in traditional microfluidic fabrication, the team developed a batch-based water-in-oil emulsion method to produce PEDOT:PSS microparticles.
Stirring the heated emulsion disintegrates the polymer into droplets, which then crosslink into stable spherical hydrogels.
The resulting microparticles self-assemble into paste-like solids with micropores when densely packed, similar in texture to wet sand.
These structures show shear-thinning and self-healing behavior, allowing them to be injected, 3D printed, or molded, and then re-solidify when the applied force is removed.
Boosting Conductivity Without Sacrificing Mechanics
Initial conductivity varied across samples. To improve performance, researchers adjusted the PSS/PEDOT ratio, added ionic liquids, and used acetic acid post-treatment.
These modifications produced stable microparticles with up to 137 S/m conductivity and consistent performance (11.81 % variation), as confirmed by X-ray photoelectron spectroscopy and zeta potential analysis.
Crucially, these treatments did not compromise the hydrogels’ mechanical properties. Oscillatory rheology confirmed that the materials retained their desired viscoelastic behavior.
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Bioelectronic Functionality in Live Systems
To demonstrate functionality, further experiments were conducted in the university's Center for Cyborg and BioRobotic Research.
Researchers applied small clumps of the hydrogel to the antennae of locusts, which have olfactory receptor neurons.
The material successfully recorded local field potentials in response to odors, revealing its possible use as a functional bioelectronic interface.
Biocompatibility and Potential Applications
Testing with human dermal fibroblasts showed over 98 % cell viability and healthy cell growth around the microparticles, indicating strong cytocompatibility.
This supports potential applications in tissue engineering scaffolds, injectable therapies, and 3D-printed electrodes for monitoring or stimulating encapsulated cells.
The work was led by Alexandra Rutz, assistant professor of biomedical engineering at the McKelvey School of Engineering, and Anna Goestenkors, a fifth-year doctoral student in Rutz’s lab.
Journal Reference
Goestenkors, A. P. et al. (2025). PEDOT: PSS Microparticles for Extrudable and Bioencapsulating Conducting Granular Hydrogel Bioelectronics. Small, e06438. DOI: 10.1002/smll.202506438
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