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Tremendous potential for successful medical device development lies in both electrical stimulation therapies and neuronal prosthetic devices, which can be utilized in an extensive number of neurological disorders. These technologies rely on the successful electrical stimulation of biological tissue (i.e. neurons) through the use of electrodes. However, this technology faces the principal problem of poor stimulus selectivity due to the currently available electrode’s large size relative to its targeted population of neurons. Irreversible damage to both the stimulated tissue and electrode are limiting factors in miniaturization of this technology, as charge density increases with decreasing electrode size. In an attempt to find an equilibrium between these two opposing constraints (electrode size and charge density), the objective of this work was to develop a novel iridium-nickel oxide (Ir0.2-Ni0.8-oxide) coating that could intrinsically offer high charge storage capacity. Thermal decomposition was used to fabricate titanium oxide, iridium oxide, nickel oxide, and bimetallic iridium-nickel oxide coatings on titanium electrode substrates. The Ir0.2-Ni0.8-oxide coating yielded the highest intrinsic (material property) and extrinsic (material property + surface area) charge storage capacity (CSC) among the investigated materials, exceeding the performance of the current state-of-the-art neural stimulating electrode, Ir-oxide. This indicates that the Ir0.2-Ni0.8-oxide material is a promising alternative to currently used Ir-oxide, Pt, Au and carbon-based stimulating electrodes.

The aim of this study was to investigate how the electrochemical properties of porous titanium nitride stimulation electrode are affected by fibrous encapsulation in vivo . Electrochemical impedance spectroscopy (EIS), cyclic voltammetry and voltage transient (VT) measurements were performed in vivo and in phosphate buffered saline, where the encapsulation process is absent. EIS was used as a non-invasive measurement to follow the inflammation, healing and encapsulation process. EIS showed that the healing and encapsulation process lasted 3–4 weeks. The VTs increased during the first 3–4 weeks, after which they stabilized. The charge storage capacity (CSC) decreased most during the first 3–4 weeks. The increasing VTs and decreasing CSC during the first 3–4 weeks after implantation of the in vivo electrodes seem related to healing and fibrous encapsulation. It is suggested that the charge injection pathway during the encapsulation process changes, which implies that charge injection limits are underestimated with conventional methods. [ABSTRACT FROM AUTHOR]

To elevate the electrochemical stability of polypyrrole–zinc oxide (PPy–ZnO) coatings, five different electrodeposition protocols were attempted to fabricate PPy–ZnO nanocomposites on tungsten substrates. The effects of the electrodeposition schemes on the morphology, microstructure and electrochemical properties of coatings were systematically analyzed, and the long-term electrochemical stability was examined via biphasic current pulse measurement in 0.01 M phosphate-buffered saline (PBS). Results indicated that our newly coated samples displayed safer capacitive charge transform behaviors. In particular, the cathodic charge storage capacity (CCSC) and safe charge injection capacity (Q inj) of the coated sample prepared by cyclic voltammetry (CV) electrodeposition were 15.3 and 0.26 mC/cm2, respectively, which were approximately 7 times and 30% greater than those of pure substrate. Moreover, the coated sample also showed perfect long-term electrochemical stability with no delamination, cracks, or ridges on the coating surface. This improvement is mainly attributed to CV electrodeposition, which smoothed the polymer morphology, compacted the structure, enhanced the interface adhesion, and diminished the internal micropores, leading to minimized volumetric expansion and shrinking of coatings in the long-term charge/discharge process. [Display omitted] • Electrochemical properties of W electrodes can be promoted by coated PPy–ZnO films. • Compacter structure of PPy–ZnO nanocomposites were obtained by CV method. • Dense structure helps to improve the electrochemical stability of the coating. • Porous structure is adverse to the electrochemical stability of the coating. [ABSTRACT FROM AUTHOR]

Iridium oxide films formed by electrodeposition onto noniridium metal substrates are compared with activated iridium oxide films (AIROFs) as a low impedance, high charge capacity coating for neural stimulation and recording electrodes. The electrodeposited iridium oxide films (EIROFs) were deposited on Au, Pt, PtIr, and 316 LVM stainless steel substrates from a solution of IrCl/sub 4/, oxalic acid, and K/sub 2/CO/sub 3/. A deposition protocol involving 50 potential sweeps at 50 mV/s between limits of 0.0 V and 0.55 V (versus Ag|AgCl) followed by potential pulsing between the same limits produced adherent films with a charge storage capacity of >25 mC/cm/sup 2/. Characterization by cyclic voltammetry and impedance spectroscopy revealed no differences in the electrochemical behavior of EIROF on non-Ir substrates and AIROF. The mechanical stability of the oxides was evaluated by ultrasonication in distilled water followed by dehydration and rehydration. Stability under charge injection was evaluated using 200 /spl mu/s, 5.9 A/cm/sup 2/ (1.2 mC/cm/sup 2/) cathodal pulses. Loss of iridium oxide charge capacity was comparable for AIROFs and the EIROFs, ranging from 1% to 8% of the capacity immediately after activation or deposition. The EIROFs were deposited and evaluated on silicon microprobe electrodes and on metallized polyimide electrodes being developed for neural recording and stimulation applications. [ABSTRACT FROM PUBLISHER]