Neuro-stimulation can be implemented using several design choices — bipolar vs. monopolar stimulation, current vs. voltage control, and active vs. passive recharge. To ensure proper function through the desired lifetime, electrodes are typically made of titanium, platinum, or iridium. The difference between the 3 metals is primarily based on their performance in reversible oxidation/reduction mechanisms, which can be illustrated using various electrochemical techniques.
In slow cyclic voltammetry analysis, a platinum electrode can reversibly consume and release 3 mC/cm2 of charge within the normal operating voltage range. However, for actual neuro-stimulation pulses, platinum can only safely inject 0.1 mC/cm2, as estimated from an electrode-potential graph. Compared to platinum, iridium can inject 10 times the amount of charge for both neuro-stimulation and cyclic voltammetry. The greater capability is due to both the greater number of available oxidation states and utilization of bulk porous oxide.
In AC impedance, a titanium electrode exhibits the same double-layer capacitance per area as that of platinum. However, titanium suffers from irreversible buildup of a high-impedance oxide layer, which prevents sustained charge-injection usage. The irreversible oxidation can be observed using the pulse-clamp technique.
This chapter also introduces computer simulations, specifically capacitive computer models, as a method for visualizing the current-distribution pattern. The simulation shows uniform current distribution despite prominent electrode topologies. A dissolution study performed with gold electrodes confirms that the current distribution is uniform during normal usage, but exhibits severe current crowding when charge injection is increased above the safe limit.
Tremiliosi-Filho G, Jerkiewicz G, Conway BE (1992) Characterization and significance of the sequence of stages of oxide film formation at platinum generated by strong anodic polarization. Langmuir 8:658CrossRefGoogle Scholar
Pikelny AY (2003) Mechanism of platinum deterioration under stimulation pulses polarization. IFESSGoogle Scholar
Petit MA, Plichon V (1997) Anodic electrodeposition of iridium oxide films. J Electroanal Chem 444:247–252CrossRefGoogle Scholar
Weiland JD, Anderson DJ, Humayun MS (2002) In vitro electrical properties for iridium oxide versus titanium nitride stimulating electrodes. IEEE Trans Biomed Eng 49:1574–1579CrossRefGoogle Scholar
Wessling B, Besmehn A, Mokwa W et al. (2007) Reactively sputtered iridium oxide. J electroch Soc 154:f83–f89CrossRefGoogle Scholar
Pourbaix M (1974) Atlas of electrochemical equilibria in aqueous solutions. Pergamon Press, BrusselsGoogle Scholar
Beebe X, Rose TL (1988) Charge injection limits of activated iridium oxide electrodes with 0.2 ms pulses in bicarbonate buffered saline. IEEE Trans Biomed Eng 35:6CrossRefGoogle Scholar
Robblee LS, McHardy J, Marston JM, Brummer SB (1980) Electrical stimulation with Pt electrodes V The effect of protein on Pt dissolution. Biomaterials 1(3):135–139CrossRefGoogle Scholar
Hibbert DB, Weitznera K, Tabor B, Carter P (2000) Mass changes and dissolution of platinum during electrical stimulation in artificial perilymph solution. Biomaterials 21(1):2177–2182CrossRefGoogle Scholar
Norlin A, Pan J, Leygraf C (2005) Investigation of electrochemical behavior of stimulation/sensing materials for pacemaker electrode applications I Pt, Ti, and TiN coated electrodes. J Electrochem Soc 152 (2):J7–J15CrossRefGoogle Scholar
Meyer RD, Cogan SE, Nguyen TH et al. (2001) Electrodeposited iridium oxide for neural stimulation and recording electrodes. IEEE Trans Neural Sys Rehab 9:2CrossRefGoogle Scholar
Robblee LS, McHardy J, Agnew WF et al. (1983) Electrical stimulation with Pt electrodes VII, Dissolution of Pt electrodes during electrical stimulation of the cat cerebral cortex. J Neurosci Methods 9(4):301–308CrossRefGoogle Scholar
Scheiner A, Mortimer JT, Roessmann U (1990) Imbalanced biphasic electrical stimulation: muscle tissue damage. Ann Biomed Eng 18(4): 407–425CrossRefGoogle Scholar
Rose TL, Robblee LS (1990) Electrical stimulation with Pt electrodes VIII Electrochemically safe charge injection limits with 0.2 ms pulses. IEEE T BioMed Eng 37:1118CrossRefGoogle Scholar
Campbell SA, Kim HS, Gilmer DC et al. (1999) Titanium dioxide (TiO2)-based gate insulators. IBM J Res Dev 43(3):383–392CrossRefGoogle Scholar
Bonner M, Daroux M, Crish T et al. (1993) The pulse-clamp method for analyzing the electrochemistry on neural stimulating electrodes. J Electrochem Soc 140:2740CrossRefGoogle Scholar
Hung A, Zhou D, Greenberg R et al. (2007) Pulse-clamp technique for characterizing neural-stimulating electrodes. J Electrochem Soc 154(9):479–486CrossRefGoogle Scholar
Moorhead ED, Stephens MM (1990) A finite element Galerkin/B-spline (GBS) numerical model of electrochemical kinetics, transport, and mechanism for multi-geometry working electrodes II: A study of quasi-reversible linear sweep voltammetry. J Electroanal Chem 282(1):1–26CrossRefGoogle Scholar
Speiser B (1996) Numerical simulation of electroanalytical experiments: recent advances in methodology. Electroanal Chem 19:1–108Google Scholar
Feldberg SW (1972) Electrochemistry, calculations, simulations and instrumentations. Marcel Dekker, New YorkGoogle Scholar
Goldberg IB, Bard AJ (1972) Resistive effects in thin electrochemical cells: digital simulations of current and potential steps in thin layer electrochemical cells. Electroanal Chem 38:313CrossRefGoogle Scholar
Ferrigno R, Brevet PF, Girault HH (1997) Finite element simulation of the chrono-amperometric response of recessed and protruding microdisc electrodes. Electrochimica Acta 42(12):1895–1903Google Scholar
Mcintyre CC, Grill WM (2001) Finite element analysis of the current-density and electric field generated by metal microelectrodes. Ann Biomed Eng 29(3):227–235Google Scholar
Rubinstein JT, Spelman FA, Soma M (1987) Current-density profiles of surface mounted and recessed electrodes for neural prostheses. IEEE Trans Biomed Eng 34 (11):864–875CrossRefGoogle Scholar
Ksienski DA (1992) A minimum profile uniform current-density electrode. IEEE Trans BioMed Eng 39(7):682CrossRefGoogle Scholar
Brummer SB, Turner MJ (1977) Electrical stimulation with Pt electrodes: II-estimation of maximum surface redox limits. IEEE Trans BioMed Eng 24:440CrossRefGoogle Scholar
Hung A (2005) Techniques for sensing the current distribution and charge storage of high-density neuroelectrodes. PhD Thesis UCLAGoogle Scholar
Hung A, Zhou D, Greenberg R et al. (2005) Dynamic simulation and testing of the electrode-electrolyte interface of 3-D stimulating microelectrodes. IEEE Neural Eng, March 16–19Google Scholar