Determining the Functional Nanostructure of Conducting Polymers in Bioelectronics by Electron Microscopy

Doctoral thesis, 2026

Advances in diagnostics and therapies for brain disorders are opening new treatment options. While typical treatments rely on biochemical mechanisms and invasive electrical therapies, electronic neuro-pharmaceuticals have recently emerged as an alternative. These pharmaceuticals are based on organic electronic devices created in vivo within brain tissue. The material of such devices must be soft enough to integrate with the tissue, conduct both electronic and ionic signals, and be small enough for the brain. Water-soluble thiophene-based monomer precursors of conducting polymers are promising candidates. These monomers have been used to create bioelectronics through polymerisation in neuromorphic organic electrochemical transistors (OECTs), on living neural cells, and in conducting hydrogels.
 
This thesis focuses on the functional micro- and nanostructure of conducting polymers in bioelectronics and the thin film evolution during growth. The material structures are studied using transmission electron microscopy (TEM), liquid phase TEM (LPTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). This work shows that the morphology of electropolymerised transistor channels for OECTs is influenced by the surface for film growth, with a smooth polymer film forming directly on surface modified OECT substrates. Subsequent growth on the polymer surface leads to a more rough surface morphology. This work includes method development of in situ and ex situ LPTEM setups to enable studies of monomer solutions in their native state. LPTEM imaging of such solutions reveals nanoscale aggregation, which impacts the morphology of OECT films in regions of low electric potential where large aggregates containing nanoscale features are present. This thesis also includes studies of enzymatically polymerised coatings on neural cells as well as conducting hydrogels which can be used as scaffolds for three-dimensional neural cell cultures. The studies show that cells polymerised in suspension acquire a patchy, conducting thin film coating that adheres to the outside of the cell membrane and covers part of the cell surface. The porosity of the hydrogels is a key factor for their performance. SEM analysis shows that increased conducting polymer content in the hydrogels leads to larger pore sizes but reduced interconnectivity. The findings in this work provides important structural information needed to understand and optimise the properties of neuro-pharmaceuticals.