Performance of platinum stimulating electrodes mapped on the limitvoltage plane

The corrosion of platinum electrodes in saline is studied by measuring loss of metal resulting from the passage of current and plotting the data on the electrode fimit-voltage plane (ELVP). Some results show that with this form of presentation, the effects of current density, pauses in the current and the presence of blood serum (to imitate extracellular fluid), is not strong. Evidence shows that in these neutral solutions corrosion occurs when the positive voltage excursion is great enough for acid to be evolved locally by the oxidation of water. When electrode voltage is not controlled and it is capacitor-coupled (e.g. in practical stimulators). serum has a beneficial effect on the voltage, tending to reduce corrosion.     

Linear and nonlinear properties of platinum electrode polarisation. Part 1: frequency dependence at very low frequencies

The polarisation impedance of the platinum electrode was measured in physiological saline (0·9% NaCl) over six decades of frequencies down to 1 mHz. The applicability, of Fricke’s phase angle rule was verified down to 10 mHz. The resistive shunt which emerges at lower frequencies was shown to be equivalent to the direct current (d.c.) impedance of the interface. A Cole-Cole (1941) type of relaxation model is proposed to describe the interface behaviour over all frequency ranges. Nonlinear polarisation measurments have demonstrated the validity of Schwan’s limit law of linearity at very low frequencies.     

Long-term implantation of platinum electrodes: Effects on electrode material and nerve tissue

Electrical stimulation of nerves has become an established method in long-term treatment of patients with disturbances in the central or peripheral nervous system. This type of treatment raises questions as to the long-term consequences of implantation in terms of tissue and electrode reactions. The aim of the present study was to find out whether the structure of peripheral nerve tissue is altered after long-term contact with platinum electrodes and the way in which platinum electrodes are changed by prolonged implantation. The study was performed in six dogs which had undergone experiments in which stimulation electrodes were placed bilaterally on the carotid sinus nerves. Fibrotic changes in the nerve bundle and the perineurium were observed after 12·5 years. Accumulation of organic material on the electrode surface was revealed by Auger electron spectroscopy. The surfaces of the implanted electrodes had oxidised and had a high concentration of carbon and measurable amounts of sulphur, indicating corrosion.     

Platinum and platinum/iridium electrode properties when used for extracochlear electrical stimulation of the totally deaf

Little work has been reported which characterises the electrical behaviour of electrode materials used for extracochlear stimulation. Electrode properties were investigated to optimise preparation methods and facilitate the design of electrode driving circuitry. Electrode preparation techniques were developed in vitro, using a combination of electrochemical measurements and scanning electron microscopy. Electrochemical etching gave the lowest observed impedances. Four subjects were each temporarily implanted with two active extracochlear electrodes, one of pure platinum and another of electrochemically etched platinums/10 per cent iridium alloy impedance measurements were taken over a ten-day implantation period and were interpreted by a simple electrical model. Constant-current stimulation was perceptually more effective than voltage-controlled excitation for the same energy input. Stimulation dynamic ranges were measured and used to estimate design limits for practical stimulators. The effect of changing electrode diameters was studied in vitro and was related to the same model. The best in vitro analogue of the in vivo environment was found to be dilute isotonic saline.     

Nanostructured platinum grass enables superior impedance reduction for neural microelectrodes

Micro-sized electrodes are essential for highly sensitive communication at the neural interface with superior spatial resolution. However, such small electrodes inevitably suffer from high electrical impedance and thus high levels of thermal noise deteriorating the signal to noise ratio. In order to overcome this problem, a nanostructured Pt-coating was introduced as add-on functionalization for impedance reduction of small electrodes. In comparison to platinum black deposition, all used chemicals in the deposition process are free from cytotoxic components. The grass-like nanostructure was found to reduce the impedance by almost two orders of magnitude compared to untreated samples which was lower than what could be achieved with conventional electrode coatings like IrOx or PEDOT. The realization of the Pt-grass coating is performed via a simple electrochemical process which can be applied to virtually any possible electrode type and accordingly shows potential as a universal impedance reduction strategy. Elution tests revealed non-toxicity of the Pt-grass and the coating was found to exhibit strong adhesion to the metallized substrate.     

Scanning electron microscopy of chronically stimulated platinum intracochlear electrodes

Platinum electrodes were examined for evidence of corrosion using a scanning electron microscope (SEM). In vivo electrodes, stimulated using charge-balanced biphasic pulses for periods of up to 2000 h at charge densities of 0.18-0.32 microC mm-2 geom. per phase, were compared with in vitro electrodes stimulated in inorganic saline using similar stimulus parameters, and with in vivo control electrodes. The in vitro stimulated electrodes showed evidence of platinum corrosion at high charge density and aggregate charge injection. Significantly, the in vivo stimulated electrodes showed no evidence of stimulus induced corrosion. Indeed, their surfaces were similar to the in vivo control electrodes. In vitro electrochemical studies have demonstrated that proteins play a significant role in the inhibition of platinum dissolution: the present study has demonstrated an inhibitory effect in vivo. This may be due to the presence of proteins.     

Linear and nonlinear properties of platinum electrode polarisation III: Equivalence of frequency-and time-domain behaviour

The polarisation properties of a platinum electrode in physiological saline (0·9 per cent NaCl) were studied in the linear and nonlinear range both in the frequency and time domains (parts 1 and 2). A model which states the limits of linear behaviour in the time domain is presented, its validity tested against experimental data and its equivalence with the analogous expression in the frequency domain demonstrated.     

Computation of the impedance characteristic of metal electrodes for biological investigations

In a previous study, basic electrochemistry was used to derive analytical expressions for the equivalent network components of the a.c. impedance of biological needle electrodes. In the present paper, numerical parameter values are determined and inserted into these expressions. Matching of computer-calculated characteristics with experimental results has been used to determine certain constants, which are difficult to determine in a more direct way. The electrode impedance at very low frequencies turns out to be almost purely resistive in character and mainly determined by the exchange current density of the metal-electrolyte system. In the intermediate-frequency range the diffusion impedance together with the double-layer capacitance are the decisive factors. The magnitude of the impedance diminishes here with fⁿ, where ?1相似文献   

Electrical characteristics of conductive yarns and textile electrodes for medical applications

Clothing with conductive textiles for health care applications has in the last decade been of an upcoming research interest. An advantage with the technique is its suitability in distributed and home health care. The present study investigates the electrical properties of conductive yarns and textile electrodes in contact with human skin, thus representing a real ECG-registration situation. The yarn measurements showed a pure resistive characteristic proportional to the length. The electrodes made of pure stainless steel (electrode A) and 20% stainless steel/80% polyester (electrode B) showed acceptable stability of electrode potentials, the stability of A was better than that of B. The electrode made of silver plated copper (electrode C) was less stable. The electrode impedance was lower for electrodes A and B than that for electrode C. From an electrical properties point of view we recommend to use electrodes of type A to be used in intelligent textile medical applications.     

Different storage methods for biopotential skin electrodes (sintermetallic Ag/AgCl) and their influence on the bias potential

Summary The aim of the present study was to investigate the influence of various methods of storage on the Differences in Electrode Potential (DEP). For periods of 22 h each, 10 Ag/AgCl sintered metal biopotential skin electrodes were stored in 4 media: dry, in a 0.9% NaCl solution, in distilled water and in electrode jellies. When storing the electrodes in 0.9% NaCl, distilled water, and electrode jelly all the electrodes of one make were stored together in a container filled with the medium in question, with and without the application of an external short circuit. After storage the electrodes were filled with one of 3 electrode jellies (Beckman Electrode Electrolyte, Parker Spectra 360, Siemens Electrode Gel). The DEPs between each two electrodes were measured 10, 30, 60 and 120 min after filling. The results show no difference for the two makes of electrodes (Beckman and IVM), but clear differences (up to factor 50) were observed in the electrode jellies used. The method of storage has a significant influence on the DEP. Dry storage yielded the lowest values (p<0.001) for all electrodes and electrode jellies (x between 84 and 318 V) and the highest stability. When stored in 0.9% NaCl, distilled water and electrode jelly, both with and without external short circuit, the electrodes showed DEPs in the mV range and drifted strongly during the period of observation, except after short-circuited storage in 0.9% NaCl, when a phase of stability is reached after 60 min.This project was supported by a grant from the österreichischer Fonds zur Förderung der wissenschaftlichen Forschung     

Effects of a potent antioxidant, platinum nanoparticle, on the lifespan of Caenorhabditis elegans

We have shown that platinum nanoparticles (nano-Pt) are a superoxide dismutase (SOD)/catalase mimetic. Various data have shown extension of the Caenorhabditis elegans lifespan by antioxidant treatment. The present study was designed to elucidate the survival benefit conferred by nano-Pt, as compared to the well-known SOD/catalase mimetic EUK-8. At 0.5mM, nano-Pt significantly extended the lifespan of wild-type N2 nematodes and at 0.25 and 0.5mM, nano-Pt recovered the shortened lifespan of the mev-1(kn1) mutant, which is due to excessive oxidative stress. In both instances, EUK-8 at 0.05, 0.5, and 5mM did not extend nematode lifespan. Even when 0.4M paraquat was loaded exogenously, nano-Pt (0.1 and 0.5mM) and EUK-8 (0.5 and 5mM) were effective in rescuing worms. Moreover, 0.5mM nano-Pt significantly reduced the accumulation of lipofuscin and ROS induced by paraquat. We measured the in vitro dose-dependent quenching of O(2)(-) and H(2)O(2), indicating that nano-Pt is a more potent SOD/catalase mimetic than EUK-8. Nano-Pt prolonged the worm lifespan, regardless of thermotolerance or dietary restriction. Taken together, nano-Pt has interesting anti-ageing properties.     

Theory and design of capacitor electrodes for chronic stimulation

Conventional metal electrodes generate electrochemical byproducts during stimulation of nerve or muscle. These byproducts may cause tissue damage, especially with the long-term stimulation necessary with neural prosthetic devices. To prevent the possibility of such damage, completely insulated electrodes have been devised which deliver current pulses by capacitive charging of the electrode surface, not involving electrochemical reactions. Anodised discs of porous tantalum, 1·0 mm in diameter and 0·25 mm thick, can deliver 0·5 ms, 5 mA pulses. Such electrodes are available as components of commercial capacitors and are easily adapted for biological use. The design may be optimised by mathematical analysis of an equivalent electrical circuit.In vitro tests demonstrate a clear advantage of these electrodes over capacitively coupled platinum-iridium electrodes in preventing oxidation-reduction reactions. The electrodes are stable on chronic implantation and should provide a safer interface between neural prosthetic devices and human tissue.     

Subcellular localization of platinum in the guinea pig after treatment with cisplatin

X-ray microprobe analysis was performed to elucidate the distribution of platinum as a marker of cisplatin. Cisplatin was administered to guinea pigs. Organs sensitive to the toxic side-effect of this drug were studied at an ultrastructural level. 1) Platinum was detected in single-membraned, presumably lysosomal bodies; platinosomes. 2) Platinosomes containing platinum were found in the proximal tubular cells of kidneys, Kupffer cells and hepatocytes in livers. However, platinum was not detected in the nucleus or other compartments of these cells. 3) Platinum was found even in the inner ear, especially in the stria vascularis and the basal lamina in the organs of Corti. Platinum was localized in the lysosomal structures in the cytoplasm, but not in the nucleus. The mechanism of side-effects of cisplatin was discussed.     

Investigation into the origin of the noise of surface electrodes

In the recording of biomedical signals, a significant noise component is introduced by the electrode. The magnitude of this noise is considerably higher than the equivalent thermal noise from the electrode impedance. As the noise in surface electrodes limits the resolution of biopotential recordings, it is important to understand its origin. It was found that the noise mainly originates in the electrolyte-skin interface and that it is highly dependent on the electrode gel used and the skin properties of the test subject. Depending on skin treatment, magnitudes between 1 and 20μV_rms were measured among subjects. When the metal-electrolyte interface was allowed time to stabilise, electrodes of different metals measured face to face all showed a negligibly small noise magnitude (<1μV_rms). In pre-gelled electrodes, where the metal-electrolyte interface has stabilised, no difference in noise properties was found between Ag−AgCl electrodes and other metals when measured on the skin. In subjects at rest, the contribution of EMG signals to the total noise level was shown to be negligibly small compared with the noise contribution of the electrolyte-skin interface. The magnitude of the noise of electrodes appeared to be inversely proportional to the square root of the area of the electrode on the skin.     

Comparison of electrode impedances of Pt,PtIr (10% Ir) and Ir-AIROF electrodes used in electrophysiological experiments

In tissue impedance measurements with the 4-electrode assembly, unexpected difficulties may occur because a combination of electrode impedance and stray capacitance in the array of four electrodes, can lead to serious measuring failures in the low-frequency range. An optimal solution to this problem can be obtained if the electrode impedances are frequency independent. A comparative study of the electrode impedances of Pt and PtIr electrodes and of a new electrode material (Ir-AIROF) is reported. It is shown that the impedance of Ir-AIROF electrodes is relatively low and almost frequency independent. Therefore the use of Ir-AIROF electrodes provides a solution to the problem mentioned above.     

Noise of surface bio-potential electrodes based on NASICON ceramic and Ag−AgCl

The electrochemical noise from dry NASICON-based surface electrodes and pregelled Ag−AgCl electrodes is evaluated in saline solutions and on the skin. The electrochemical noise from the electrode/electrolyte interface is found to be negligible (less than 1 μV peak to peak). On the skin, the noise level is highly dependent on the patient. At high frequencies, the skin/electrode interface noise is equal to ‘thermal noise’ and can be related to the real part of the skin/electrode impedance. At low frequencies (f<100 Hz), excess noise is observed that varies as f⁻². It is tentatively ascribed to a non-stationary process or noise of electrochemical origin due to the ionic nature of the skin. The contribution of residual EMG signal of low amplitude (5 μV peak to peak) is suggested for electrodes with large surface area. Reprint requests and correspondence should be addressed to Frist     

Linear and nonlinear properties of platinum electrode polarisation II: time domain analysis

The linear and nonlinear transient behaviour of a platinum electrode in physiological saline (0·9% NaCl) was investigated. The interface overpotential (current) in response to a step current (voltage) was monitored over six decades of pulse duration starting at 10 μs, both in the linear range, i.e. where the polarising current and the polarisation voltage are proportional, and in the nonlinear range, where this proportionality is lost. The time invariance of the Pt electrode/physiological saline interface parameters in the linear range and at the onset of nonlinearity over the studied band of frequencies and pulse durations is deduced from the equivalence of experimental results obtained in the frequency and time domains using the appropriate transformation when mapping the two domains. We conclude that the interface can be analysed and modelled in either domain in the linear range and at the onset of nonlinearity.     

同型半胱氨酸电极的研制及其测定性能研究

建立一种血浆中同型半胱氨酸（HCY）的含量测定方法。以 HCY 为目标分子,α－甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯作交联剂,偶氮二异丁腈（AIBN）作为引发剂,制备了 HCY 分子印迹模板,并以此为电活性物质研制了 HCY 电极,用以建立血液中 HCY 的测定方法。HCY 在5×10－3 mol ／L ～5×10－5 mol ／L 范围内与电池电动势呈现良好的 Nernst 响应,r 为0．9992,并用大鼠血浆进行了加样回收,平均回收率为101．3％,RSD 为2．71％。HCY 电极响应性能良好,可用于真实样品的测定。