Two-Photon Polymerization of 3D Electrically Conductive Scaffolds for Neuronal Cell Studies

Abstract

The brain is the most intricate organ in the human body, yet the underlying mechanisms of its cells and networks are not fully mapped. In addition to this lack of understanding, there are numerous neurological disorders and diseases for which a cure remains elusive. There has been persistent research to understand how neuronal cells function when interfaced to engineered biomaterials. The mechanical, topological, and chemical features of the extracellular matrix influence neuronal cell growth, and, among these, also electrical cues play a fundamental role in steering cell fate. The importance of electrical stimulation and 3D engineered microenvironments, better mimicking the spatial configuration followed by cells in the natural brain tissue, necessitates therefore the design of electrically conductive 3D microstructures. In light of the limited number of 3D electrically conductive scaffold studies, their reproducibility issues as well as fabrication constraints, the aim of this thesis is to at develop 3D electrically conductive free-standing microstructures made of polymeric materials. To achieve this goal, a protocol involving the chemical oxidative polymerization of EDOT (3,4-ethylene dioxythiophene) into PEDOT, an electrically conductive polymer, is developed. To ensure conductivity throughout polymeric 3D microstructures, EDOT is incorporated into an acrylate-based resin (IP-L) and 3D printed via twophoton polymerization (2PP), a 3D printing technology with sub-micrometre resolution. The electrical conductivity is experimentally measured, and it is reported how the tuning of printing parameters and organic solvents have a significant influence, with a maximum conductivity of 17.43 S/m after Dimethyl sulfoxide (DMSO) treatment. The mechanical properties of the 2PP-printed structures are evaluated as well, highlighting that the stiffness of microstructures decreases as EDOT doping increases. The versatility of the developed approach is demonstrated by fabricating 3D cage matrices featuring geometries suitable for neuronal cell culture. The reported results pave the way to further investigate the effect of 3D electrically conductive PEDOT-doped microstructures on neuronal cell growth and development.