Investigating Biocompatibility of PEDOT-based Biopolymers for Enhanced Integration into Neuronal Networks

In the neuroelectronics field, neuromorphic devices based on organic electrochemical transistors (OECTs) are important, as they emulate neuronal features such as short- and long-term synaptic plasticity and adaptivity¹ because of the characteristic mixed ionic-electronic conduction mechanism of conjugated polymers like poly(3,4 ethylene dioxythiophene) – PEDOT:PSS. Depending on the application, aside from PSS⁻, PEDOT can be doped with negatively charged counterions such as hexafluorophosphate (PF⁶⁻) or perchlorate (ClO₄⁻).^2,3 Moreover, functionalization of PEDOT:PSS with azobenzene group <i>via</i> click chemistry produces photo-responsive azo-PEDOT:PSS biopolymers.⁴ To achieve full integration of OECT-based neuromorphic devices into neuronal networks, the interface between biological cells and biopolymers is critical.⁵ The surface geometry, biomaterial roughness, and its chemical composition can affect the neuron-material interfaces, neuron morphology, and network development. Developing new biomaterials with improved features in terms of stability and conductivity are in demand to achieve seamless integration and broaden the biological applications of OECTs considering also the potential role of different counterions in triggering neuronal outgrowth at the cell-chip interface.<br/><br/>In this work, the interfaces of cells and semiconductive PEDOT-based biopolymers—PEDOT:PSS, PEDOT:PF₆, PEDOT:ClO₄, and modified PEDOT-crown:ClO₄^₆ are investigated. The PEDOTcrown:ClO₄ is interesting owing to its ability to bind Na⁺, which can mimic sodium channels that are abundantly expressed in the nervous system. The interfaces of cells and N₃-PEDOT:PSS, N₃-PEDOT:PF₆, and N₃-PEDOT:ClO₄, which can be functionalized into photo-responsive azo-PEDOT, are also studied. The biocompatibility of the biopolymers is investigated by assessing the viability and morphology of HT22 neuronal cells on each material. To assess the HT22 survival rate and cytotoxicity, standard <i>in vitro</i> assays (Live/Dead, MTT, and cellular ROS) are used. Cell morphology is assessed by labeling the actin cytoskeleton. The focused ion beam/scanning electron microscopy (FIB/SEM)⁷ is used to gain a deeper insight into cell-biomaterial interfaces. Currently, biocompatibility assays and FIB/SEM are being carried out to investigate primary neuron-biomaterial interfaces. Also, neuron overgrowth on biopolymers is being studied by actin labeling in the growth cones and by immunostaining of axons and dendrites.<br/><br/>The results of this study are of importance since they will provide a characterization of new semiconductive biomaterials with potential applications in the neuro- and optoelectronics fields.<br/><br/>1. Bruno, U. et al., "Integration of Neuronal Networks" (Neuromorphic Comput. Eng. 2023).<br/>2. Donahue, M. J. et al., "Tailoring PEDOT for Bioelectronics" (Mat. Sci. Eng. R Rep. 2020).<br/>3. Skorupa, M. et al., "Dopant-Dependent PEDOT Functionality in Bioelectronics" (Polymers 2021).<br/>4. Corrado, F. et al., "Azobenzene Transistors for Neurohybrid Building Blocks" (Nat. Commun. 2023).<br/>5. Rinklin, P. & Wolfrum, B., "Recent Developments in Neuroelectronic Devices" (Neuroforum 2021).<br/>6. Kousseff, C. J. et al., "Controlled PEDOT Film Morphology for Electrochromic Behavior" (J. Polymer Sci. 2022).<br/>7. Santoro, F. et al., "Revealing the Cell–Material Interface with Nanometer Resolution by Focused Ion Beam/Scanning Electron Microscopy" (ACS Nano 2017).