Polypyrrole-coated electrodes for the delivery of charge and neurotrophins to cochlear neurons

Biomaterials. 2009 May;30(13):2614-24. doi: 10.1016/j.biomaterials.2009.01.015. Epub 2009 Jan 29.

Abstract

Sensorineural hearing loss is associated with gradual degeneration of spiral ganglion neurons (SGNs), compromising hearing outcomes with cochlear implant use. Combination of neurotrophin delivery to the cochlea and electrical stimulation from a cochlear implant protects SGNs, prompting research into neurotrophin-eluting polymer electrode coatings. The electrically conducting polypyrrole/para-toluene sulfonate containing neurotrophin-3 (Ppy/pTS/NT3) was applied to 1.7 mm2 cochlear implant electrodes. Ppy/pTS/NT3-coated electrode arrays stored 2 ng NT3 and released 0.1 ng/day with electrical stimulation. Guinea pigs were implanted with Ppy/pTS or Ppy/pTS/NT3 electrode arrays two weeks after deafening via aminoglycosides. The electrodes of a subgroup of these guinea pigs were electrically stimulated for 8 h/day for 2 weeks. There was a loss of SGNs in the implanted cochleae of guinea pigs with Ppy/pTS-coated electrodes indicative of electrode insertion damage. However, guinea pigs implanted with electrically stimulated Ppy/pTS/NT3-coated electrodes had lower electrically-evoked auditory brainstem response thresholds and greater SGN densities in implanted cochleae compared to non-implanted cochleae and compared to animals implanted with Ppy/pTS-coated electrodes (p<0.05). Ppy/pTS/NT3 did not exacerbate fibrous tissue formation and did not affect electrode impedance. Drug-eluting conducting polymer coatings on cochlear implant electrodes present a clinically viable method to promote preservation of SGNs without adversely affecting the function of the cochlear implant.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cochlea / cytology*
  • Electric Stimulation
  • Electrodes
  • Female
  • Guinea Pigs
  • Male
  • Nerve Growth Factors / chemistry*
  • Nerve Growth Factors / metabolism*
  • Neurons / metabolism*
  • Polymers / chemistry*
  • Prostheses and Implants
  • Pyrroles / chemistry*

Substances

  • Nerve Growth Factors
  • Polymers
  • Pyrroles
  • polypyrrole