In Vivo Electrochemical Analysis of a PEDOT/MWCNT Neural Electrode Coating

Abstract

Neural electrodes hold tremendous potential for improving understanding of brain function and restoring lost neurological functions. Multi-walled carbon nanotube (MWCNT) and dexamethasone (Dex)-doped poly(3,4-ethylenedioxythiophene) (PEDOT) coatings have shown promise to improve chronic neural electrode performance. Here, we employ electrochemical techniques to characterize the coating in vivo. Coated and uncoated electrode arrays were implanted into rat visual cortex and subjected to daily cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for 11 days. Coated electrodes experienced a significant decrease in 1 kHz impedance within the first two days of implantation followed by an increase between days 4 and 7. Equivalent circuit analysis showed that the impedance increase is the result of surface capacitance reduction, likely due to protein and cellular processes encapsulating the porous coating. Coating’s charge storage capacity remained consistently higher than uncoated electrodes, demonstrating its in vivo electrochemical stability. To decouple the PEDOT/MWCNT material property changes from the tissue response, in vitro characterization was conducted by soaking the coated electrodes in PBS for 11 days. Some coated electrodes exhibited steady impedance while others exhibiting large increases associated with large decreases in charge storage capacity suggesting delamination in PBS. This was not observed in vivo, as scanning electron microscopy of explants verified the integrity of the coating with no sign of delamination or cracking. Despite the impedance increase, coated electrodes successfully recorded neural activity throughout the implantation period.

Ultrasoft microwire neural electrodes improve chronic tissue integration

“…Furthermore, methods need to be developed to fabricate multi-channel devices. In addition, conducting polymer and nanomaterial modifications of the electrode sites to improve neural recording specificity and long-term quality can greatly expand the versatility of this device [25,49,101]. Additional modifications to include bioactive coatings that promote neuronal health and reduce acute inflammation may further improve electrode tissue integration [51,53,102–105].…”

Neuroadhesive L1 coating attenuates acute microglial attachment to neural electrodes as revealed by live two-photon microscopy

“…This includes changing the footprint of the probe or the probe’s electrode sites [18,36,44,47–51,160], altering recording site materials [48,52–57], applying flexible geometries or soft materials [26,27,36,58–62,161,162], creating dissolvable insertion shuttles for softer probe materials [63], locally delivering anti-inflammatory or neuroprotective drugs [64–75], and modifying the probe’s surface chemistry [36,76–78]. …”

Dexamethasone retrodialysis attenuates microglial response to implanted probes in vivo

“…Numerous intervention strategies to minimize the inflammatory tissue responses to neural implants have been proposed and/or investigated including device footprint size [44, 51, 52], electrode site size [44, 53], volumetric density across the device’s footprint [54, 55], strength [44, 56], compliance/flexibility [44, 57], elasticity/softness [58–61], electrical properties [62–66], device insertion speed [67, 68], tip shape[67], surface modifications [44, 69–71 and 109], and drug delivery [27–29, 72–79]. In particular, dexamethasone (Dex), an anti-inflammatory synthetic glucocorticoid, has been frequently used to reduce inflammation and the reactive tissue response around surgical implants [80, 81], and more recently for use with brain implants [27–29, 72–79, 82].…”