Abstract
Conducting polymers have been extensively reported as promising coating materials for applications involving interactions with electrically excitable tissues. Specifically, metal electrodes functionalized with conducting polymer coatings have been employed as biointerfaces presenting tailored properties to promote electrode integration as well as chronic functionality. Currently, polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) represent the most extensively studied conducting polymers, exhibiting favourable electrochemical properties and biocompatibility. In this paper, we study electrodeposited poly(3,4-ethylenedioxypyrrole) (PEDOP), a conducting polymer which is structurally related to both PEDOT and PPy, and is expected to outperform its “parent” polymers in terms of electrochemical properties and biocompatibility. The performance of PEDOP doped with chloride/phosphate, p-toluenesulfonate or polystyrene sulfonate was subsequently investigated to assess the efficacy of these ionic dopants in promoting electrochemical stability and neural cytocompatibility. Electrodeposited PEDOP films exhibited a high charge storage capacity (50.07 ± 6.96 mC cm−2), charge injection capacity (203 ± 24 μC cm−2) and substantial stability (performance loss of 0.49 ± 0.06% after 100 000 stimulation pulses). Furthermore, PEDOP films promoted enhanced neuron outgrowth and viability relative to control substrates. In particular, PEDOP/PTS was shown to increase the average neurite length by a factor of three when compared with cells cultured on bare Pt control substrates. Consequently, due to its favourable electrochemical characteristics together with high neural cytocompatibility, PEDOP can be indicated as a promising alternative to PPy and PEDOT in the field of neural science.
Highlights
Conducting polymers have been used for biomedical engineering purposes for the last 25 years [1,2], due to their unique ability to combine the electrical properties of metallic materials and chemomechanical properties of polymers [3]
The optimal polymerisation conditions were identified individually for PEDOP/phosphate buffer saline (PBS), PEDOP/PTS and PEDOP/polystyrene sulfonate (PSS), in order to find the most favourable potential range leading to the formation of the polymer with advantageous electrochemical performance, in terms of low impedance and high charge storage capacity (Fig.S1-S3), as well as mechanical stability high enough to withstand sterilization procedure
The current peak associated with monomer oxidation was observed to decrease due to the consumption of the monomer leading to the formation of dimers, oligomers, and, polymer chains
Summary
Conducting polymers have been used for biomedical engineering purposes for the last 25 years [1,2], due to their unique ability to combine the electrical properties of metallic materials and chemomechanical properties of polymers [3]. It follows that an ideal material for tissue engineering applications should possess the favorable water solubility and low oxidation potential of pyrrole, together with high stability of PEDOT Related to both PEDOT and PPy, poly(3,4-ethylenedioxypyrrole) (PEDOP) exhibits a combination of the qualities of its “parent” polymers, resulting in the formation of a superior conducting material [16,17]. The most well studied dopants for oxidative polymerization include buffer salts and perchlorates, and more recently, aromatic sulfonate compounds, such as p-toluenesulfonate (PTS) and polystyrene sulfonate (PSS) [5] These dopants are known for providing conducting polymers with numerous beneficial properties, including their significant biocompatibility and processability [7,27]. The optimization protocol involved changing the oxidation potential of the polymerization process in order to form a polymer with superior electrochemical characteristics, in terms of high CSC and low impedance module at 1 kHz, as well as the mechanical stability high enough to withstand the sterilization procedure (Fig.S1-S3)
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