(J-382) Optimizing Electrochemical Properties of Biomimetically Synthesized Conjugated Conductive Polymer Nanoparticles for Applications in Neurostimulation and Neuroengineering

Introduction:: Due to the nervous system’s limited capacity for spontaneous regeneration and functional recovery, traumatic brain and nerve injuries often lead to a permanent decrease in a patient’s quality of life. Conjugated conductive polymers are receiving increasing attention due to their biocompatibility, soft tissue-like mechanical properties, and high electrical and ionic conductivity, which make them ideal materials for neuronal stimulation and for compatible interfaces with neurons. We have recently reported the use of the capacitive behavior of standalone 3,4-ethylenedioxythiophene-pyrrole (EDOT-Py) copolymer Nano-Particles (NPs) doped with poly(styrene sulfonate) (PSS) for neuron differentiation and for evoking neural activity.¹ Being able to tune a material’s electrochemical properties is essential to optimize biomedical effects of the material. In this work, the effect of varying the doping agent PSS molecular weight (MW) and size distribution on the electrochemical properties of EDOT-Py NPs are studied.


Materials and Methods:: PSS with varying MW was synthesized using Reverse Addition Fragmentation Chain-Transfer (RAFT) polymerization and Free Radical Polymerization (FRP) to obtain narrow and broad size distributions, respectively. Biomimetic synthesis of EDOT-Py copolymer NPs doped with p-toluenesulfonic acid and PSS was carried out using hematin as a catalyst. High Performance Liquid Chromatography/Gel Permeation Chromatography (HPLC/GPC) were used to characterize PSS MW. PSS and EDOT-Py NPs were characterized by means of Raman spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). EDOT-Py NPs’ electrochemical properties were characterized by galvanostatic charge discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Live-Dead assay was performed on mouse neuroblastoma x rat dorsal root ganglion neuron hybrid cell line (ND7/23) to assess EDOT-Py NPs’ biocompatibility.

Results, Conclusions, and Discussions:: Characterization of PSS conducted by Raman Spectroscopy presented bands at 1127 and 1035 cm⁻¹ assigned to ν(SO) modes of undissociated sulfonic acid and sulfonate groups (Figure 1a). EDOT-Py copolymer presented coincidence with bands obtained for the homopolymers (PEDOT and PPy). The obtained EDOT-Py NPs presented sizes in the range of 200-600 nm (Figure 1b-c) and surface zeta potentials in the -20 to -30 mV range, irrespective of PSS MW and size distribution. On the other hand, electrochemical properties were highly dependent on the dopant characteristics. The largest specific capacitance was obtained for EDOT-PY NPs doped with low molecular weight, RAFT synthesized PSS. Conductive polymer nanoparticles obtained here presented good biocompatibility towards ND7/23 cells.


Varying MW and size distribution of PSS doping agent is an effective and biocompatible way of tuning EDOT-Py copolymer’s electrochemical properties, free of possibly toxic chemical post-treatments. Biomimetically EDOT-Py copolymer nanoparticles synthesized here are appealing materials for neurostimulation and as constituents of neural electrodes and scaffolds.


Acknowledgements (Optional): : This research was supported, in part, by NSF EEC-1852560.

References (Optional): : ACS Appl. Nano Mater. 2022, 5, 8, 12006–12018