Electropolymerized Poly(3,4-ethylenedioxythiophene) (PEDOT) Coatings for Implantable Deep-Brain-Stimulating Microelectrodes

Abstract

Conducting polymers have been widely explored as coating materials for metal electrodes to improve neural signal recording and stimulation because of their mixed electronic–ionic conduction and biocompatibility. In particular, the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT) is one of the best candidates for biomedical applications due to its high conductivity and good electrochemical stability. Coating metal electrodes with PEDOT has shown to enhance the electrode’s performance by decreasing the impedance and increasing the charge storage capacity. However, PEDOT-coated metal electrodes often have issues with delamination and stability, resulting in decreased device performance and lifetime. In this work, we were able to electropolymerize PEDOT coatings on sharp platinum-iridium recording and stimulating neural electrodes and demonstrated its mechanical and electrochemical stability. Electropolymerization of PEDOT:tetrafluoroborate was carried out in three different solvents: propylene carbonate, acetonitrile, and water. The stability of the coatings was assessed via ultrasonication, phosphate buffer solution soaking test, autoclave sterilization, and electrical pulsing. Coatings prepared with propylene carbonate or acetonitrile possessed excellent electrochemical stability and survived autoclave sterilization, prolonged soaking, and electrical stimulation without major changes in electrochemical properties. Stimulating microelectrodes were implanted in rats and stimulated daily, for 7 and 15 days. The electrochemical properties monitored in vivo demonstrated that the stimulation procedure for both coated and uncoated electrodes decreased the impedance.

Poly(3,4-ethylenedioxyselenophene): effect of solvent and electrolyte on electrodeposition, optoelectronic and electrochromic properties

“…This difference in the electrochemical behaviour due to solvents is explained by slow and smooth growth of longer polymer chains in PC which results in faster electron transfer. 36,51 A similar trend was noticed in the CV of PMDTO lms prepared in MeCN and PC. 36 It is noteworthy to mention that the redox behaviour of PEDOS lms were also considerably inuenced by supporting electrolytes.…”

“…This indicates the formation of polymer lms with more ordered structure due to slow process for lm growth resulting in smooth and compact morphology. 34,36,51 It was noted that lms prepared using TBABF 4 showed more compact structure and smooth morphologies as compared to lms prepared using TBAPF 6 and TBAClO 4 . It is also important to mention that PEDOS lm prepared using TBABF 4 /PC has more smooth morphology as compared to other solvent-electrolyte media.…”

“…34,36 This is explained by high polarity of PC which favours the solubility of short oligomers resulting in homogeneous growth of polymer lms on the electrode surface. 51 Moreover, high viscosity of PC results in slow diffusion of species (monomer, oligomers and counter anions) during polymerization limiting the polymerization rate as compared to MeCN. This indicates the formation of polymer lms with more ordered structure due to slow process for lm growth resulting in smooth and compact morphology.…”

Conducting Polymer-Based Composite Materials for Therapeutic Implantations: From Advanced Drug Delivery System to Minimally Invasive Electronics

“…Few researches have focused on solving these problems by doping inorganic and organic substances into the ICP coating to enhance the adhesion between the ICP films and the substrates and also to enhance the biocompatibility of the electrodes corresponding to the neural tissues. For example, Bodart et al polymerized PEDOT:tetrafluoroborate (PEDOT:BF 4 ) onto the platinum neural electrode by using three different solvents, i.e., propylene carbonate (PC), acetonitrile (ACN), and water [71]. The mechanical and electrochemical stabilities of the as-obtained composited electrodes were subsequently analyzed.…”

Physiological Artefacts and the Implications for Brain-Machine-Interface Design

“…In practice, this can be challenging in brain stimulation systems that use "monopolar" stimulation between the electrode and the case. The best-case scenario is then to use active recharge, which limits the time duration of the case connection [21]. One opportunity to relax these requirements is to lower the tissue-electrode impedance with surface coatings like PEDOT or Ti-N [22], [23].…”