Platinum-iridium Research Articles

Biocompatibility and magnetic resonance imaging characteristics of carbon nanotube yarn neural electrodes in a rat model.

BackgroundImplantation of deep brain stimulation (DBS) electrodes is a landmark therapy for movement disorders and some mental conditions. Compared to conventional platinum–iridium (Pt–Ir) electrodes, carbon nanotube yarns (CNTY) electrodes have improved stability and interface characteristics with less distortion during high field strength MRI. Sprague–Dawley rat models were used to examine thein vivo histological and imaging properties of biocompatible CNTY throughout the subacute period.MethodsSprague–Dawley rats received CNTY (n = 16) or Pt–Ir control (n = 16) electrodes. Behavioral markers, body weight, and survival were recorded. Comparative histology (HE, NeuN, CD68, and GFAP) was performed at 1, 6, and 12 weeks post-implantation; 3.0T MRI was performed at 1 and 12 weeks.ResultsOf 32 rats, 30 (15 per group) survived implantation without reduced activity, paralysis, or incapacity to feed. Following implantation, progressive decreases in macrophage activation and neuron-depleted margins surrounding electrodes were observed in both groups. Inflammatory marker expression (CD68) was significantly lower in rats with implanted CNTY electrodes compared to controls at all time points. CNTY electrodes also caused less inflammation and shallower depths of macrophage penetration and neural disruption relative to the interface. Artifacts and distortion were observed on MRI of Pt–Ir but not CNTY electrodes.ConclusionsCNTY electrodes exhibited reduced inflammatory margins compared to Pt–Ir electrodes throughout the subacute period, indicating reduced initial trauma, better overall biocompatibility, and reduced fibrous tissue formation. Coupled with less MRI distortion, CNTY electrodes may be useful alternatives when there is a need to monitor electrode placement by MRI.Electronic supplementary materialThe online version of this article (doi:10.1186/s12938-015-0113-6) contains supplementary material, which is available to authorized users.

Method for determining ion exchange membrane resistance for electrodialysis systems

Ion transport resistance is an important characteristic of ion exchange membranes. It is not a constant but is influenced by among other things the salt concentration in the external solution. A vast number of publications investigated the membrane resistance; however, the use of different methods leads to different results. Different approaches and possible flaws are discussed and a method for measuring membrane resistance is developed, evaluated, and described. It is shown that this method can be used in a wide concentration range of 0.001–5M NaCl. The method is based on electrical impedance spectroscopy within an electrochemical cell containing four electrodes. An AC is applied on two work electrodes, while two thin platinum iridium wires are used as reference electrodes to evaluate the sample impedance. Membrane resistance is obtained from a differential impedance measurement of a solution without and with a membrane. Resistance of AMX and CMX membranes is determined.

Improving traceability to the international prototype of the kilogram

Until a new definition of the kilogram has been adopted, the SI unit of mass remains defined in terms of an artefact, the international prototype of the kilogram which is not readily available for regular recalibration of BIPM prototypes used for the calibration of national prototypes. Since 1889 the working hypothesis has been that the platinum–iridium prototypes are stable mass standards, although mass comparisons indicate that this is not entirely true. In this paper we present a method for improving metrological traceability to the international prototype by modelling the change in mass of prototypes over time and evaluate the model parameters by a weighted least squares adjustment. The method has been applied to comparisons between 18 prototypes performed at the BIPM in the period 1889–2009. The mass values predicted by the model are compared to the mass values assigned by BIPM in the period 1992–2009 and to results of the Extraordinary Calibrations performed at BIPM in 2014 using the international prototype as reference standard.

Fabrication of Low-Invasive Patch Glucose Sensors

1. IntroductionRecently, implantable glucose sensors for continuous glucose monitoring (CGM) are provided significant advantage on diabetic health care, since it not only lower the physical and mental load on glucose measurement, but also present continuous glucose trend, which is useful for treatment evaluation. However, since the length of sensor device inserted in skin is about 1 cm, development of lower invasive CGM system is expected for the improvement of diabetic patients' quality of life. In this study, a fine needle tube type glucose sensor, which has sensing region at the tip of a fine tapered electrode, was proposed. The schematic illustration of such glucose sensor is shown in Fig. 1. Since the sensing region is at the tip of tapered electrode, it only requires the sensor tip to be implanted in the tissue for glucose monitoring, which makes it possible to perform as a patch type sensor instead of implanting sensor. Fine platinum-iridium alloy wire was placed inside the tapered PEEK tube and glucose oxidase (GOx) was immobilized on the surface of platinum electrode by using the combination of electrodeposition and electropolymerization technique. Properties of the obtained sensor were evaluated mainly by in vitro measurement.2．ExperimentalPt-Ir alloy wire (0.17 mm in diameter) was fixed in a PEEK tube (0.20 mm in inner diameter and 0.8 mm in outer diameter). The prepared assembly was mechanically polished to form a fine tapered needle structure. According to the procedure proposed by Wilson's group [1], the biosensor was prepared.The amperometric responses of the prepared electrodes to glucose were examined at 40°C in a 0.1 M PBS (pH 7.4) containing 0.1 M NaCl, by measuring the electrooxidation current at a potential of 0.6 V (vs. Ag/AgCl).3．ResultsCurrent-time response of the prepared electrode was investigated. The response current increased with increasing concentration of glucose. Response current provided good linear relationship with glucose concentration. Variation of response in time on the prepared electrode was investigated for two weeks. The response of the electrode was measured at 40°C and stored in phosphate buffer at 4°C when not in use. After initial increase of response current for few days, the electrode provided stable response current.(1) N. Matsumoto, X. Chen and G. S. Wilson, Anal Chem, 74, 368 (2002). Figure 1

Determination of the amount of physical adsorption of water vapour on platinum–iridium surfaces

This paper presents the measurement of the physical adsorption of water vapour on platinum–iridium surfaces using a vacuum mass comparator. This value is of importance for redefining the kilogram, which will be realized under vacuum in the near future. Mirror-polished artefacts, consisting of a reference artefact and a test artefact, were manufactured for this experiment. The surface area difference between the reference and test artefacts was 226.2 cm2. This surface area difference was approximately 3.2 times the geometric surface area of the prototype of the kilogram made of platinum–iridium (71.7 cm2). The measurement results indicate that the amount of physical adsorption at a relative humidity of 50% is 0.0129 μg cm, with a standard uncertainty of 0.0016 μg cm. This value is 0.03 to 0.16 times that observed in other studies.

In vivo comparison of the charge densities required to evoke motor responses using novel annular penetrating microelectrodes.

Electrodes for cortical stimulation need to deliver current to neural tissue effectively and safely. We have developed electrodes with a novel annular geometry for use in cortical visual prostheses. Here, we explore a critical question on the ideal annulus height to ensure electrical stimulation will be safe and effective. We implanted single electrodes into the motor cortex of anesthetized rats and measured the current required to evoke a motor response to stimulation, and the charge injection capacity (CIC) of the electrodes. We compared platinum iridium (PtIr) electrodes with different annulus heights, with and without a coating of porous titanium nitride (TiN). Threshold charge densities to evoke a motor response ranged from 12 to 36 μC.cm-2.ph-1. Electrodes with larger geometric surface areas (GSAs) required higher currents to evoke responses, but lower charge densities. The addition of a porous TiN coating did not significantly influence the current required to evoke a motor response. The CIC of both electrode types was significantly reduced in vivo compared with in vitro measurements. The measured CIC was 72 and 18 μC.cm-2.ph-1 for electrodes with and without a TiN coating, respectively. These results support the use of PtIr annular electrodes with annulus heights greater than 100 μm (GSA of 38, 000 μm2). However, if the electrodes are coated with porous TiN the annulus height can be reduced to 40 μm (GSA of 16,000 μm2).

In vivo comparison of the charge densities required to evoke motor responses using novel annular penetrating microelectrodes.

Electrodes for cortical stimulation need to deliver current to neural tissue effectively and safely. We have developed electrodes with a novel annular geometry for use in cortical visual prostheses. Here, we explore a critical question on the ideal annulus height to ensure electrical stimulation will be safe and effective. We implanted single electrodes into the motor cortex of anesthetized rats and measured the current required to evoke a motor response to stimulation, and the charge injection capacity (CIC) of the electrodes. We compared platinum iridium (PtIr) electrodes with different annulus heights, with and without a coating of porous titanium nitride (TiN). Threshold charge densities to evoke a motor response ranged from 12 to 36 μC.cm-2.ph-1. Electrodes with larger geometric surface areas (GSAs) required higher currents to evoke responses, but lower charge densities. The addition of a porous TiN coating did not significantly influence the current required to evoke a motor response. The CIC of both electrode types was significantly reduced in vivo compared with in vitro measurements. The measured CIC was 72 and 18 μC.cm-2.ph-1 for electrodes with and without a TiN coating, respectively. These results support the use of PtIr annular electrodes with annulus heights greater than 100 μm (GSA of 38, 000 μm2). However, if the electrodes are coated with porous TiN the annulus height can be reduced to 40 μm (GSA of 16,000 μm2).

Cardiac Resynchronization Therapy Delivered Via a Multipolar Left Ventricular Lead is Associated with Reduced Mortality and Elimination of Phrenic Nerve Stimulation: Long-Term Follow-Up from a Multicenter Registry.

Lower Mortality and Eliminated PNS Associated with Quadripolar LeadsIntroductionCardiac resynchronization therapy (CRT) using quadripolar left ventricular (LV) leads provides more pacing vectors compared to bipolar leads. This may avoid phrenic nerve stimulation (PNS) and allow optimal lead placement to maximize biventricular pacing. However, a long‐term improvement in patient outcome has yet to be demonstrated.MethodsA total of 721 consecutive patients with conventional CRTD criteria implanted with quadripolar (n = 357) or bipolar (n = 364) LV leads were enrolled into a registry at 3 UK centers. Lead performance and mortality was analyzed over a 5‐year period.ResultsPatients receiving a quadripolar lead were of similar age and sex to those receiving a bipolar lead, although a lower proportion had ischemic heart disease (62.6% vs. 54.1%, P = 0.02). Both groups had similar rates of procedural success, although lead threshold, impedance, and procedural radiation dose were significantly lower in those receiving a quadripolar lead. PNS was more common in those with quadripolar leads (16.0% vs. 11.6%, P = 0.08), but was eliminated by switching pacing vector in all cases compared with 60% in the bipolar group (P < 0.001). Furthermore, LV lead displacement (1.7% vs. 4.6%, P = 0.03) and repositioning (2.0% vs. 5.2%, P = 0.03) occurred significantly less often in those with a quadripolar lead. All‐cause mortality was also significantly lower in the quadripolar compared to bipolar lead group in univariate and multivariate analysis (13.2% vs. 22.5%, P < 0.001).ConclusionsIn a large, multicenter experience, the use of quadripolar LV leads for CRT was associated with elimination of PNS and lower overall mortality. This has important implications for LV pacing lead choice.

Selective ligandless cloud point extraction of palladium from water and dust samples.

In this study, the phase-separation phenomenon of non-ionic surfactants was used for separation and preconcentration of Pd(II). The cloud point extraction (CPE) method is based on the formation of PdI2 which is then entrapped in the non-ionic surfactant Triton X-114. Ethanol acidified with 0.5 M HNO3 was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry. The main factors affecting CPE efficiency, such as sample solution pH, concentration of iodide ion and Triton X-114, equilibration temperature and time, were all investigated and optimized. At optimum conditions, a calibration curve was constructed for the determination of palladium according to the ligandless CPE procedure. Linearity was maintained between 1.0 to 500.0 ng/mL. The LOD based on three times the SD of the blank divided by the slope of analytical curve, (3Sb/m) was 0.3 ng/mL. Seven replicate determinations of a solution containing of 4.0 μg palladium gave a mean absorbance of 0.359 with RSD±1.85%. The high efficiency of CPE to carry out the determination of palladium in complex matrixes was demonstrated. The proposed method has been applied to the determination of trace amounts of palladium in a platinum-iridium alloy, water, and dust samples, with satisfactory results.

Electrochemical red-ox therapy of prostate cancer in nude mice

Minimally invasive therapies are increasingly in demand for organ-confined prostate tumors. Electrochemical therapy (EChT) is attractive, as it relies on locally-induced reduction–oxidation reactions to kill tumor cells. Its efficacy for prostate cancer was assessed in human PC-3 and LNCaP tumor xenografts growing subcutaneously in nude mice (n=80) by applying 2 Stainless Steel vs. 4 Platinum–Iridium (Pt–Ir) electrodes to deliver current densities of 10 to 35mA/cm2 for 30 or 60min. The procedure was uneventful in 90% of mice. No difference in tumor vs. body temperature was observed. Changes at electrode-tumor junctions were immediate, with dryness and acidity (pH2–3) at the anode and oedema and alkalinity (pH10–12) at the cathode. This was accompanied by cellular alterations, found more pronounced at the cathode. Such acidic and alkaline conditions were cytotoxic in vitro and dissolved cells at pH>10. In mice, tumor destruction was extensive by 24h with almost undetectable blood prostate specific antigen (LNCaP model) and covered the whole tumor surface by 4days. EChT was most efficient at 25–30mA/cm2 for 60min, yielding the longest recurrence-free survival and higher cure rates, especially with 4 Pt–Ir electrodes. EChT is a promising option to optimize for organ-confined prostate tumors.

Study of degradation intermediates formed during electrochemical oxidation of pesticide residue 2,6-dichlorobenzamide (BAM) at boron doped diamond (BDD) and platinum–iridium anodes

Electrochemical oxidation is a promising technique for degradation of otherwise recalcitrant organic micropollutants in waters. In this study, the applicability of electrochemical oxidation was investigated concerning the degradation of the groundwater pollutant 2,6-dichlorobenzamide (BAM) through the electrochemical oxygen transfer process with two anode materials: Ti/Pt90–Ir10 and boron doped diamond (Si/BDD). Besides the efficiency of the degradation of the main pollutant, it is also of outmost importance to control the formation and fate of stable degradation intermediates. These were investigated quantitatively with HPLC–MS and TOC measurements and qualitatively with a combined HPLC–UV and HPLC–MS protocol. 2,6-Dichlorobenzamide was found to be degraded most efficiently by the BDD cell, which also resulted in significantly lower amounts of intermediates formed during the process. The anodic degradation pathway was found to occur via substitution of hydroxyl groups until ring cleavage leading to carboxylic acids. For the BDD cell, there was a parallel cathodic degradation pathway that occurred via dechlorination. The combination of TOC with the combined HPLC–UV/MS was found to be a powerful method for determining the amount and nature of degradation intermediates.

Pressure Induced Phase Transition and Superconducting Properties of PtH and IrH: A First Principles Study

The electronic, structural, mechanical and superconducting properties of PtH and IrH are investigated using first principles calculation based on density functional theory with generalized gradient approximation. The calculated lattice constants at normal pressure are in good agreement with experimental and other theoretical results. Among the five crystallographic proposed structures investigated, the cubic phase is found to be more stable than the hexagonal ones. A new high pressure CsCl phase is predicted for Iridium hydride. The maximum superconducting transition temperature achieved in Platinum hydride and Iridium hydride are 23.8K and 10K respectively. The calculated elastic constants indicate that both the hydrides are mechanically stable at ambient pressure. PACS: 61.50.Ks, 31.15.A-, 62.20.-x, 74.20.pq

Controlled metallic nanopillars for low impedance biomedical electrode

Radial metallic nanopillar/nanowire structures can be created by a controlled radiofrequency (RF) plasma processing technique on the surface of certain alloy wires, including important biomedical alloys such as MP35N (Co–Ni–Cr–Mo alloy), platinum–iridium and stainless steel. In electrode applications such as pacemakers or neural stimulators, the increase in surface area in elongated MP35N nanopillars allows for decreased surface impedance and greater current density. However, the nanopillar height on MP35N alloy tends to be self-limiting at ∼1–3μm. The objective of this study was to further elongate the radial nanopillars so as to reduce electrode impedance for biomedical electrode applications. Intelligent experimental design allowed for efficient investigation of processing parameters, including plasma material, process duration, power, pressure and repetition. It was found that multi-step repeated processing in the parameter-controlled RF environment could increase nanopillar height to ∼10μm, a 400% improvement, while the RF plasma processing with identical total duration but in a single step did not lead to desired nanopillar elongation. Measurement of electrode impedance in phosphate-buffered saline solution showed an associated decrease to one-fifth of the surface impedance of unprocessed wire for signals below 100Hz. For the purposes of this study, MP35N and Pt–Ir wires were characterized and demonstrated augmented surface impedance properties which, in combination with superior cell integration, enhanced biomedical electrode performance.

An electrochemical study on the positive electrode side of the zinc–cerium hybrid redox flow battery

In this study, the electrochemical behaviour of the Ce3+/4+ redox couple in methanesulfonic acid medium on various electrode substrates was investigated as a function of temperature. Carbon composite electrodes as well as platinum and platinum iridium coated electrodes were studied for their suitability in carrying out the Ce3+/4+ redox reaction. Cyclic voltammetry in 0.8moldm−3 cerium and 4.5moldm−3 methanesulfonic acid solution showed that elevated temperatures favoured the Ce3+/Ce4+ reaction on the various platinum and platinum–iridium coated substrates as well as on carbon composite surfaces. The latter electrodes showed better kinetics than the metal coatings but deteriorated badly under the high positive potentials required for the cerium reaction. The exchange current density (jo), obtained through Tafel extrapolation, polarisation resistance and electrochemical impedance spectroscopy measurements, increased with temperature over the range 25°C to 60°C. The Pt–Ir coatings gave the largest jo at 60°C and appear best suited for use as the positive electrode in the Zn–Ce redox flow battery.

Bimetallic catalyst of PtIr nanoparticles with high electrocatalytic ability for hydrogen peroxide oxidation

Carbon supported platinum–iridium bimetallic nanoparticles (PtIr/C) for the electrochemical sensing of hydrogen peroxide (H2O2) were developed. Both the cyclic voltammogram (CV) and the amperometric response indicated that PtIr/C possesses a higher oxidation current than either Pt/C or Ir/C over the detection range 0–10mM at 0.25V (vs. SCE). The addition of Ir appears to facilitate oxidation kinetics and decrease the competitive adsorption of dioxygen and oxygenated intermediates. These changes were investigated by electrochemical measurements and X-ray absorption near edge spectroscopy (XANES). This study demonstrated that the PtIr/C provide a stable platform for electrochemical sensing of H2O2-derivated biospecies without enzymes and redox mediators.

Angiotensin type 2 receptors in the intermediolateral cell column of the spinal cord: Negative regulation of sympathetic nerve activity and blood pressure

Our previous study demonstrated that AT2R in brainstem nuclei participated in the regulation of sympathetic outflow and cardiovascular function. However, the functional significance of AT2R in the intermediolateral cell column (IML) of the thoracic spinal cord in normal rats remains elusive. We hypothesized that AT2R activation in the IML exerts a sympatho-inhibitory effect. Using Western-blot analysis, immunohistochemical staining and quantitative real-time PCR, both AT1R and AT2R expressions were detected in the spinal cord. The highest AT2R protein expression was found in the IML, while AT1R expression didn't display regional differences within the gray matter. Microinjection of Ang II into the IML dose-dependently elevated mean blood pressure (MAP, employing a transducer-tipped catheter) and renal sympathetic nerve activity (RSNA, using a pair of platinum-iridium recording electrodes), which were completely abolished by Losartan, and attenuated by TEMPOL and apocynin. Activation of AT2R in the IML with CGP42112 evoked hypotension (ΔMAP: -21 ± 4 mmHg) and sympatho-inhibition (RSNA: 73 ± 3% of baseline), which were completely abolished by PD123319 and l-NAME. Blockade of AT2R in the IML with PD123319 significantly increased MAP (11 ± 1 mmHg) and sympathetic nerve activity (RSNA: 133 ± 13% of baseline). Moreover, PD123319 significantly enhanced the Ang II induced pressor response. Furthermore, in isolated IML neurons, CGP42112 treatment augmented potassium current and decreased resting membrane potential by employing whole-cell patch clamp. In the normal condition, AT2R in the IML tonically inhibits sympathetic activity through an NO/NOS dependent pathway and subsequent potassium channel activation.

Comparative assessment of iridium oxide and platinum alloy wires using an in vitro glial scar assay

The long-term effect of chronically implanted electrodes is the formation of a glial scar. Therefore, it is imperative to assess the biocompatibility of materials before employing them in neural electrode fabrication. Platinum alloy and iridium oxide have been identified as good candidates as neural electrode biomaterials due to their mechanical and electrical properties, however, effect of glial scar formation for these two materials is lacking. In this study, we applied a glial scarring assay to observe the cellular reactivity to platinum alloy and iridium oxide wires in order to assess the biocompatibility based on previously defined characteristics. Through real-time PCR, immunostaining and imaging techniques, we will advance the understanding of the biocompatibility of these materials. Results of this study demonstrate iridium oxide wires exhibited a more significant reactive response as compared to platinum alloy wires. Cells cultured with platinum alloy wires had less GFAP gene expression, lower average GFAP intensity, and smaller glial scar thickness. Collectively, these results indicated that platinum alloy wires were more biocompatible than the iridium oxide wires.

Making new history from old standards

The winds of change are blowing strongly in the International System of Units (known since 1960 as the SI). Already gone is the meter bar, artfully constructed of a platinum-iridium alloy so many years ago, an end-on X-shaped bar carefully scribed by the denizens of the International Bureau of Weights and Measures (BIPM) in Sevres, France.

Experimental investigation and characterization of nano-scale dry electro-machining

This paper presents an experimental investigation and characterization of a novel technique of nanoscale electro-machining (EM) in atmospheric air, named dry nano-EM, by using scanning tunneling microscopy (STM) as the platform for nanomachining. The electro-machining has been conducted in near field by maintaining a gap distance of 1–2nm between the Platinum–Iridium [Pt–Ir (80:20)] tool electrode and atomically flat gold substrate with the air as dielectric medium. An in situ process of evaluating the tool quality before and after machining has been used by monitoring the current–displacement (I–Z) spectroscopy curves. The mechanism of dry nano-EM has been presented as well as the machining performance of the process has been evaluated. Based on the observations, it has been established that field induced evaporation due to intense heat generated at the gap width is the primary mechanism of material removal in dry nano-EM. The experimental results show that dry nano-EM is capable of fabricating consistent nano-features with good repeatability. The volume of material removal increases almost linearly with increasing number of features machined and machining time, indicating the consistency in the dimensions of the nano-features. Finally, dry nano-EM is established as a technique capable of machining 50–100 features in a pre-defined manner with average feature size of 7.5–10nm in a single pass, thus suitable for nano-patterning in atomically flat electrically conducting surfaces.

Metal–carbon nanocomposites as the oxygen electrode for rechargeable lithium–air batteries

A key constituent in developing lithium–air batteries is the oxygen electrode, which facilitates the oxygen reduction reaction during the discharge process and the oxidation reaction of Li2O2 during the charge process. In this article, we report on the electrocatalytic activity of platinum, iridium, and platinum–iridium alloy in an oxygen electrode. The average crystallite size of the previous metal nanoparticles was less than 2nm, which were uniformly dispersed on the surface of chained Ketjenblack powder. Both chronoamperometry analysis and cell testing showed that Pt–Ir/C electrode exhibited superior activity and is the best electrode in this research. The discharge potentials for all three catalysts are similar, ∼2.81V vs. Li/Li+, and the discharge overpotential (∼0.15V) is very low. The charge overpotential for Pt–Ir/C composites was around 0.6V.