Determining the Functional Nanostructure of Polymeric Systems for Electronic Neuro-Pharmaceuticals by Electron Microscopy

Licentiate thesis, 2024

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 creating organic electronic devices in vivo within brain tissue. The material of such devices must be soft enough to integrate with the central nervous system 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 biocompatible electrodes through in vivo polymerisation in living organisms, in neuromorphic organic electrochemical transistors (OECTs), and in conducting hydrogels. However, the detailed structure of the materials in these bioelectronics is not well known. Knowledge about the material structure is important for understanding and optimising the physical properties.
 
This thesis uses electron microscopy to investigate the micro- and nanostructure of polymeric systems for electronic neuro-pharmaceuticals. The evolution of material structures is studied using transmission electron microscopy (TEM), liquid-phase TEM, 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. In addition, large aggregates containing nanoscale features are found in the film. Imaging of monomer solutions reveals nanoscale aggregation, which impacts the morphology of OECT films in regions of low electric potential. This thesis also studies enzymatically polymerised conducting hydrogels, which show promise as scaffolds for 3D neural cell cultures. The porosity of the hydrogels is a key factor. SEM analysis shows that increased conducting polymer content leads to larger pore sizes but reduced interconnectivity. The findings in this work provide important structural information needed to understand and optimise the properties of neuro-pharmaceuticals.