Chronic recordings from micromachined neural electrode arrays often fail a few weeks after implantation primarily due to the formation of an astro-glial sheath around the implant. We propose a drug delivery system, from conducting polymer (CP) coatings on the electrode sites, to modulate the inflammatory implant-host tissue reaction. In this study, polypyrrole (PPy) based coatings for electrically controlled and local delivery of the ionic form of an anti-inflammatory drug, dexamethasone (Dex), was investigated. The drug was incorporated in PPy via electropolymerization of pyrrole and released in PBS using cyclic voltammetry (CV). FTIR analysis of the surface showed the presence of Dex and polypyrrole on the coated electrode. The thickness of the coated film was estimated to be ~50 nm by ellipsometry. We were able to release 0.5 µg/cm 2 Dex in 1 CV cycle and upto 92% Dex after 30 CV cycles. In-vitro studies and immunocytochemistry on murine glial cells suggest that the released drug lowers the count of reactive astrocytes to the same extent as the added drug. In addition, the released drug is not toxic to neurons as seen by healthy neuronal viability in the released drug treated cells.

Various formulations of polymeric hydrogels were synthesized and evaluated with the goal of developing a novel skin-surface biopotential electrode. Materials explored within the study included poly(2-hydroxyethyl methacrylate) (polyHEMA) in pure form or impregnated with the conducting polymers polypyrrole or poly(3,4-ethylenedioxythiophene) (PEDOT), as well as polyacrylate. The drying dynamics, ionic conductivity, and impedance of the prototype materials were characterized when applied to porcine and human skin, in order to determine their utility for a minimum preparation and low specific impedance surface electrode. The addition of a fraction of PEDOT or polypyrrole within a polyHEMA gel was found to decrease hydrogel impedance when tested within PBS, as well as on non-abraded porcine skin. A polyacrylate component added to polyHEMA had no significant effect on hydrogel impedance in PBS, but significantly reduced impedance on the porcine skin surface. Although having much lower specific impedance (impedance normalized by the contact area) than the commercial skin surface electrode (3M Red Dot), polyHEMA based electrodes require skin abrasion. Pure cross-linked polyacrylate gel was found to provide the most attractive option, and yielded competitive low-impedance performance on non-abraded human skin.