Bioactive Conducting Polymer Coatings for Implantable Neural and Cochlear Electrodes.

Abstract

Neural prostheses facilitate communication with the nervous system for the diagnosis, treatment, and recovery from neurological illness or trauma. These devices require permanently implanted electrodes that provide a stable electrical connection to the nervous system and do not produce adverse effects. Unfortunately, the biological reaction to implanted electrodes often leads to the formation of fibrous tissue that limits charge transfer and renders longterm performance unreliable. This dissertation presents the development and characterization of novel electrode coatings that promote functional integration at the tissue-electrode interface. The primary constituent of these coatings is the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). PEDOT is a suitable material for interfacing electrodes with tissue because it is biocompatible, conducts both electronic and ionic charge, is easily functionalized with cells and biomolecules, and mediates the mechanical differences between electrodes and tissue. In addition, deposition of PEDOT-based coatings on individual electrode sites is rapid and reproducible. To form electrode coatings containing live cells or cellular components, PEDOT was deposited around living neuroblastoma and primary cortical neurons. These coated electrodes had 73% lower 1 kHz impedance than uncoated metal while delivering live cells to direct the tissue response. Spongy coatings were made from PEDOT deposited in alginate hydrogel containing live cells and were capable of delivering over 25 times more current than electrodes without PEDOT. Laser-patterning of PEDOT was performed to produce electrode coatings capable of directing neuronal growth. Laser interference patterning of PEDOT resulted in the alignment of up to 87% of neurites in the direction of the pattern without affecting electrical conductivity. Evaluation of conducting polymer and hydrogel coatings on cochlear implants was performed. Coatings on cochlear electrodes reduced the electrode impedance by 80% at and 99% at 1 kHz and 10.7 Hz, respectively. These coated electrodes also delivered BDNF directly within the cochlea, increasing levels of the neurotrophin to 30.3 ng/ml after one week from a baseline of 1.7 ng/ml. In deafened guinea pigs, coated cochlear implants had less chance of failure than uncoated implants. After 6 months, their final average 1 kHz impedance was 5870 Ω compared to 1.2*106 Ω for uncoated implants.