Abstract
Conducting polymer (CP) electrodes are a promising alternative to metallic electrodes, demonstrating superior electrochemical charge transfer within biological systems. However, the benefit of CPs in vitro has not been realised in vivo due to persistence of the foreign body response. One approach to overcoming this limitation is the incorporation of bioactive factors within CPs to mitigate the inflammatory response. However, incorporation of large biomolecules significantly degrades the mechanical stability of CPs.
This thesis investigated the incorporation of small bioactive factors in the CP poly(3,4-ethylene dioxythiophene) (PEDOT). It was hypothesised that smaller biomolecules may preserve CP mechanical properties. The bioactive molecules dexamethasone phosphate (DP), a powerful anti-inflammatory drug, and valproic acid (VA), an anti-inflammatory and neuroprotective agent, were investigated as bioactive dopants for PEDOT. The resulting physico-mechanical, electrochemical and biological properties were assessed. Bioactive PEDOT was found to maintain the beneficial electrochemical properties of CPs while being capable of significant attenuation of inflammation in vitro. Despite using smaller bioactive factors, the mechanical robustness of the CP was compromised, making them an unsuitable solution.
To address mechanical limitations, a conducting hydrogel (CH) was developed consisting of PEDOT grown within poly(vinyl alcohol) (PVA). CHs combine the mechanical properties of hydrogels with the electrical functionality of CPs. The formation of interpenetrating networks (IPN) of the two polymer components is essential to the fabrication of optimal CHs. To promote IPNs, PVA was chemically modified to incorporate covalently linked taurine doping molecules, designed to increase interaction between the polymer networks. The impact of taurine density and distribution within the PVA, was characterised both for the homogenous hydrogel and the resultant CH following growth of PEDOT within the PVA. IPN formation was examined through the physical, mechanical and electrochemical properties of the PEDOT/PVA-taurine. It was found that inter-dopant spacing along the PVA was critical to controlling growth of CP throughout the hydrogel. Smaller inter-dopant spacing encouraged the formation of IPNs.
Finally, DP and VA were incorporated within PEDOT/PVA CHs. Coatings maintained their hydrogel-like mechanical properties and the incorporated molecules exhibited bioactivity. Future work will focus on the impact of CH biofunctionalisation on the in vivo inflammatory response.