Extracellular Matrix-Compatible Additive Manufacturing of Bioactive, Conducting Polymer Hydrogel Electrodes

Hydrogels of conducting polymers provide a soft and hydrated alternative to metal for interfacing electronic devices with biological systems. To fabricate devices based on conducting polymer hydrogels, the material is often patterned alongside bioinert and stiff substrates such as plastics and elastomers which lead to poor cell-material interactions. In order to further promote device integration with cells and tissue, one strategy is to utilize bioactive materials, such as mammalian extracellular matrix (ECM) components, as the substrate material to present a tissue-like microenvironment to cells. However, traditional semiconductor manufacturing is anticipated to impair the bioactivity of these natural materials. Here, we demonstrate methods for mild temperature additive manufacturing of highly conducting poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) hydrogels with collagen substrates. Various types and concentrations of gelation agents were investigated to enable sufficient working time after addition to colloidal dispersions and to result in a water-stable hydrogel network once fully crosslinked. Among gelation agents tested, ionic liquid was found to be suitable for extrusion-based printing while an acidic surfactant enabled deposition by jetting due to low surface tension and appropriate viscosity. After room temperature gelation and treatment, hydrated PEDOT:PSS prints exhibited conductivity as high as 37.2 S/cm and were stable in cell culture conditions for at least 28 days. To complete the device, a top layer was fabricated by casting a collagen slurry onto the PEDOT:PSS prints which had a sacrificial material deposited on top to protect the intended electrodes from coverage. Once the collagen layer formed, the sacrificial material was removed with 36 °C water, leaving an unaltered PEDOT:PSS surface for direct biointerfacing. Since the fabrication methods were developed with mild temperatures and processing, the structure and bioactivity of the collagen are believed to be maintained, as evidenced by the support of fibroblast culture that reached confluency and sustained high viability for 28 days. This methodology offers a promising strategy for rapid prototyping soft, hydrated, and bioactive electronic devices that support cell attachment and proliferation.