Reduce impedance of intracortical iridium oxide microelectrodes by hydrogel coatings

The study investigated the influence of poly(vinyl alcohol)/poly(acrylic acid) interpenetrating polymer networks (PVA/PAA IPNs) hydrogel film coatings on interface stability between electrodeposited iridium oxide films (EIROF) microelectrodes and neural tissue by monitoring changes in impedance. The impedance of EIROF and PtIr microelectrodes (d = 75 μm) with and without the coatings was measured weekly, while the microelectrodes were implanted into the motor cortex of rats (n = 48) for 28 days. The results show that without PVA/PAA coatings the impedance of EIROF microelectrodes was higher than that of PtIr microelectrodes in vivo, however, the impedance of EIROF microelectrodes with coatings resulted in the lowest impedance compared to the impedance of both PtIr microelectrodes with coatings and EIROF microelectrodes without coatings through the whole test period. Moreover, compared to the EIROF microelectrodes without coatings, the impedance of EIROF microelectrodes with coatings reduced by ∼40% at day 21 after implantation. The PVA/PAA IPNs hydrogel coating acted as a stable ions conductive layer which enabled the EIROF microelectrodes to maintain its electrochemical superiority in vivo and enhanced the mechanical stability of the EIROF microelectrodes. The study demonstrates a concept of neural microelectrode modification, in which the hydrophilic property is crucial.