A technique for the long-term application of surface electrodes

A technique is reported for the long-term application of surface electrodes for ambulatory electromyographic (EMG) recording. Prior to electrode application the surrounding skin is lightly painted with tincture of benzoin. This treatment improves adherence to the skin of disposable electrodes and electrode attachment collars, reduces skin trauma associated with electrode removal, and minimizes sensitivity to electrode adhesives.     

Which Disposable Chest Electrode?

Chest electrodes are preferred to limb electrodes for cardiac monitoring, as limb movements are not restricted and produce less interference of the E.C.G. trace. Eight types of disposable chest electrodes were investigated to compare their performance, skin reactions, cost, ease of application, size, and skin–electrode impedance.Elema-Schonander electrodes were found to be the most efficient and the most expensive. In their application care was required to avoid severe skin reactions.Dracard electrodes were simple to attach, worked well without severe skin reactions, and were cheap. They are recommended for routine use. Smith and Nephew electrodes, a type of “multipoint electrodes” which do not require electrode jelly, frequently produced severe skin reactions, making them unsuitable for monitoring for periods exceeding 12 hours.     

A thin, flexible multielectrode grid for high-density surface EMG.

Although the value of high-density surface electromyography (sEMG) has already been proven in fundamental research and for specific diagnostic questions, there is as yet no broad clinical application. This is partly due to limitations of construction principles and application techniques of conventional electrode array systems. We developed a thin, highly flexible, two-dimensional multielectrode sEMG grid, which is manufactured by using flexprint techniques. The material used as electrode carrier (Polyimid, 50 microm thick) allows grids to be cut out in any required shape or size. One universal grid version can therefore be used for many applications, thereby reducing costs. The reusable electrode grid is attached to the skin by using specially prepared double-sided adhesive tape, which allows the selective application of conductive cream only directly below the detection surfaces. To explore the practical possibilities, this technique was applied in single motor unit analysis of the facial musculature. The high mechanical flexibility allowed the electrode grid to follow the skin surface even in areas with very uneven contours, resulting in good electrical connections in the whole recording area. The silverchloride surfaces of the electrodes and their low electrode-to-skin impedances guaranteed high baseline stability and a low signal noise level. The electrode-to-skin attachment proved to withstand saliva and great tensile forces due to mimic contractions. The inexpensive, universally adaptable and minimally obstructive sensor allows the principal advantages of high-density sEMG to be extended to all skeletal muscles accessible from the skin surface and may lay the foundation for more broad clinical application of this noninvasive, two-dimensional sEMG technique.     

Branched EMG electrodes for stable and selective recording of single motor unit potentials in humans.

Branched surface EMG electrodes are bipolar electrodes with the hot signal pole referenced to two or more short-circuited leading-off surfaces. This technique provides stable recording of single motor unit potentials during real movements, up to maximal muscle contractions. The selective characteristic of branched electrodes is based on the same principles as the double differential detection system and spatial filtering technique proposed later. Equi-weight calculations to assess the selectivity of different electrode types and their position are used. The main advantage of branched electrodes, especially high stability, is achieved by the wire electrode version. The design, manufacture, implementation, and application of wire electrodes are discussed in detail. During recording of motor unit potentials, electrodes are positioned subcutaneously over the muscle fascia. This positioning maximizes electrode stability. Appropriate orientation of the electrode relative to the muscle architecture ensures adequate selectivity for single motor unit recordings. Branched electrodes require ordinary EMG equipment (two or even one amplifier).     

Manufacturing and Using Piggy-back Multibarrel Electrodes for In vivo Pharmacological Manipulations of Neural Responses

In vivo recordings from single neurons allow an investigator to examine the firing properties of neurons, for example in response to sensory stimuli. Neurons typically receive multiple excitatory and inhibitory afferent and/or efferent inputs that integrate with each other, and the ultimate measured response properties of the neuron are driven by the neural integrations of these inputs. To study information processing in neural systems, it is necessary to understand the various inputs to a neuron or neural system, and the specific properties of these inputs. A powerful and technically relatively simple method to assess the functional role of certain inputs that a given neuron is receiving is to dynamically and reversibly suppress or eliminate these inputs, and measure the changes in the neuron''s output caused by this manipulation. This can be accomplished by pharmacologically altering the neuron''s immediate environment with piggy-back multibarrel electrodes. These electrodes consist of a single barrel recording electrode and a multibarrel drug electrode that can carry up to 4 different synaptic agonists or antagonists. The pharmacological agents can be applied iontophoretically at desired times during the experiment, allowing for time-controlled delivery and reversible reconfiguration of synaptic inputs. As such, pharmacological manipulation of the microenvironment represents a powerful and unparalleled method to test specific hypotheses about neural circuit function.Here we describe how piggy-back electrodes are manufactured, and how they are used during in vivo experiments. The piggy-back system allows an investigator to combine a single barrel recording electrode of any arbitrary property (resistance, tip size, shape etc) with a multibarrel drug electrode. This is a major advantage over standard multi-electrodes, where all barrels have more or less similar shapes and properties. Multibarrel electrodes were first introduced over 40 years ago ^1-3, and have undergone a number of design improvements ^2,3 until the piggy-back type was introduced in the 1980s ^4,5. Here we present a set of important improvements in the laboratory production of piggy-back electrodes that allow for deep brain penetration in intact in vivo animal preparations due to a relatively thin electrode shaft that causes minimal damage. Furthermore these electrodes are characterized by low noise recordings, and have low resistance drug barrels for very effective iontophoresis of the desired pharmacological agents.     

Temperature dependent alterations of the surface-EMG and ECG: an investigation of the electrical transfer characteristics of the human skin (author's transl)

The influence of local heating of the skin on the integrated EMG (registered with surface and subcutaneous electrodes), the amplitude of the ECG, the skin blood flow, the electrode impedance, the electrode-to-skin impedance, and the tissue impedance is investigated. Except for the increasing skin blood flow each of the variables exhibits a significant reduction with an increase in skin temperature. From these results the existence of two mechanisms is deduced mediating thermal influence on bioelectric signals picked up by surface electrodes: 1. An alteration of the signal source. 2. An alteration of the electric transfer characteristics of the tissue between signal source and electrode. Especially in quantitative surface electromyography the temperature dependence of the signal can be a source of error.     

Approaches to reduce the retroaction of long-term monitoring of bioelectric events in ergonomic field studies (author's transl)

When monitoring bioelectric signals the surface electrodes can cause a retroaction on the subject thereby introducing an error of measurement. There are two types of retroaction: physical and psycho-physiological. A physical retroaction due to the hydration process of the skin occurs if 'wet' electrodes are used for the recording of the skin conductance level (SCL) causing a continuous drift of the SCL and a decrease in sensitivity to SCL changes. Therefore a dry electrode was developed with improved performance: It exhibits less sensitivity to motion, is not subject to polarization, and features better SCL long-term stability. When recording the electrocardiogram or the electromyogram a psychophysiological retroaction occurs due to the annoyance caused by the skin-irritating abrading techniques in order to decrease the skin impedance and reduce the motion artifact. In an attempt to abandon the skin preparation whenever permissible without sacrificing the measurement accuracy a performance estimation procedure was developed. Basing on the information on the signal frequency content, the electrode contact area, the required accuracy of measurement and the amplifier input impedance a decision on the necessity of skin preparation is made. Moreover, the results of a study are reported investigating the reduction of motion artifacts by means of electrode design and appropriate electrode jelly formulation.     

Evolution in impedance at the electrode-skin interface of two types of surface EMG electrodes during long-term recordings.

The evolution in impedance at the electrode-skin interface of Beckman and Red Dot electrodes was assessed during long-term recordings. Impedance was measured between each pair of electrodes, arranged in a bipolar configuration on tibialis anterior (n=13). A waveform constructed of sinusoids of known frequencies, evenly distributed on a log scale from 1-16,384 Hz, was applied through the electrodes, and the result recorded by a DAQ system. SEMG signals were recorded at 1000 Hz during isometric dorsiflexion contractions of 30 s, performed every 15 min for 2 h. Impedance data were acquired at 65,536 Hz immediately before and after SEMG recordings. Large individual differences in impedance levels were observed at low frequencies. At high frequencies, impedance values depended only on the electrode type. Impedance decreased steadily with time for Beckman electrodes (p < 0.05), but did not decrease significantly for Red Dot electrodes. The magnitude of the reduction over time varied widely between individuals, and was related to the initial impedance values. The impedance-bandwidth product remained constant for each electrode type (95% confidence intervals 146.2-148.2 and 126.1-127.8 for Beckman and Red Dot electrodes respectively). When skin impedance is electrically modelled with a simple network containing a resistor and a capacitor, the capacitance varies with the properties of the electrode used, whereas resistance is dependent on the subject. Furthermore, the EMG spectrum is unaffected by impedance provided skin preparation is sufficient to reduce the impedance below 55 komega.     

Optimization of the bare platinum electrode as an oxygen measurement system in photosynthesis

This paper is concerned with the definition of the standard conditions required for optimum operation of the bare platinum electrode with photosynthetic samples. Experimental evidence shows the following: 1) Polarization circuits should have zero resistance; 2) The electrolyte layer between the electrodes should have a conductance higher than 54×10^{–6 –1} per mm² of platinum electrode area; 3) The electrodes should be polarized just before taking the measurements. All these facts can be interpreted in terms of phenomena occurring on the electrode: The adsorption of hydrogen on the electrode imposes the need for low resistances in the system, and oxygen consumption by the electrode is minimized by polarizing the electrodes as late as possible. This investigation increases the reliability of the bare platinum electrode and gives a basis for a comparison of the results from different experiments. Demonstrations of the pertinence of these conditions are made in our lab with the algae Dunaliella Tertiolecta.     

Gold nanograin microelectrodes for neuroelectronic interfaces

Neuroelectronic interfaces are imperative in investigating neural tissues as electrical signals are the main information carriers in the nervous system and metal microelectrodes have been widely used for recording and stimulation of nerve cells. For high performance microelectrodes, low tissue-electrode interfacial impedance and high charge injection limits are essential and nanoscale surface engineering has been utilized to meet the requirements for microelectrodes. We report a single-cell sized microelectrode, which has unique gold nanograin structures, using a simple electrochemical deposition method. The fabricated microelectrode had a sunflower shape with 1–5 (m of micropetals along the circumference of the microelectrode and 500 nm nanograins at the center. The nanograin electrodes had 69-fold decrease of impedance and 10-fold increase in electrical stimulation capability compared to unmodified flat gold microelectrodes. The recording and stimulation performance of nanograin electrodes was tested using dissociated rat hippocampal neuronal cultures. Noise levels were extremely low (2.89 μV_rms) resulting in high signal-to-noise ratio for low-amplitude action potentials (18.6–315 μV). Small biphasic current pulses (20–60 μA) could evoke action potentials from neurons nearby electrodes. This new nanostructured neural electrode may be applicable for the development of cell-based biosensors or clinical neural prosthetic devices.     

Simultaneous transdermal extraction of glucose and lactate from human subjects by reverse iontophoresis

This study investigated the possibility of simultaneously extracting glucose and lactate from human subjects, at the same skin location, using transdermal reverse iontophoresis. Transdermal monitoring using iontophoresis is made possible by the skin's permeability to small molecules and the nanoporous and microporous nature of the structure of skin. The study was intended to provide information which could be used to develop a full, biosensor-based, monitoring system for multiple parameters from transdermal extraction. As a precursor to the human study, in vitro reverse iontophoresis experiments were performed in an artificial skin system to establish the optimum current waveforms to be applied during iontophoresis. In the human study, a bipolar DC current waveform (with reversal of the electrode current direction every 15 minutes) was applied to ten healthy volunteers via skin electrodes and utilized for simultaneous glucose and lactate transdermal extraction at an applied current density of 300 microA/cm2. Glucose and lactate were successfully extracted through each subject's skin into the conducting gel that formed part of each iontophoresis electrode. The results suggest that it will be possible to noninvasively and simultaneously monitor glucose and lactate levels in patients using this approach and this could have future applications in diagnostic monitoring for a variety of medical conditions.     

Design and Fabrication of Ultralight Weight,Adjustable Multi-electrode Probes for Electrophysiological Recordings in Mice

The number of physiological investigations in the mouse, mus musculus, has experienced a recent surge, paralleling the growth in methods of genetic targeting for microcircuit dissection and disease modeling. The introduction of optogenetics, for example, has allowed for bidirectional manipulation of genetically-identified neurons, at an unprecedented temporal resolution. To capitalize on these tools and gain insight into dynamic interactions among brain microcircuits, it is essential that one has the ability to record from ensembles of neurons deep within the brain of this small rodent, in both head-fixed and freely behaving preparations. To record from deep structures and distinct cell layers requires a preparation that allows precise advancement of electrodes towards desired brain regions. To record neural ensembles, it is necessary that each electrode be independently movable, allowing the experimenter to resolve individual cells while leaving neighboring electrodes undisturbed. To do both in a freely behaving mouse requires an electrode drive that is lightweight, resilient, and highly customizable for targeting specific brain structures.A technique for designing and fabricating miniature, ultralight weight, microdrive electrode arrays that are individually customizable and easily assembled from commercially available parts is presented. These devices are easily scalable and can be customized to the structure being targeted; it has been used successfully to record from thalamic and cortical regions in a freely behaving animal during natural behavior.     

Electrode materials used for electrochemical oxidation of organic compounds in wastewater

Electrochemical oxidation (EO) of organic compounds is an outstanding technology capable of oxidizing organic pollutants to simple inorganic compounds such as H₂O and CO₂. Moreover, EO can be attributed to an energy-efficient process, since it requires only insignificant amount of energy in the form of an applied current or a potential to activate the electrodes. There is a vast variety of electrodes used in EO processes for organic compounds degradation. They are noble metal electrodes, such as Pt and Au, boron-doped diamond (BDD) electrodes, mixed metal oxide (MMO), graphite and carbon electrode, etc. In this regard, it becomes difficult to focus on existing electrode properties and characteristics and choose an anode material for a particular application. The aim of this study was to review information on existing anodes used in EO processes, their advantages and disadvantages, performance and application area. Thus far, MMO electrodes along with BDD electrodes are leading materials used in the processes of EO of dyes, pesticides, pharmaceuticals, industrial wastewaters, etc. This is due to their excellent catalytic properties and resistance to both corrosion and dissolution. The catalytic activity of MMO electrodes strongly depends not only on their composition but also on fabrication methods. Thus, a correlation was made between the methods of manufacturing, efficiency and cost in the MMO electrodes. Despite the wide variety of anodes, most of them are either relatively expensive to be used for large volumes of wastewater, or they consist of potentially toxic metals. Moreover, none of them are sufficiently efficient and stable. Therefore, cost-effective, efficient and “green” anodic materials are still under development.     

A Dynamic Selection Method for Reference Electrode in SSVEP-Based BCI

In SSVEP-based Brain-Computer Interface (BCI), it is very important to get an evoked EEG with a high signal to noise ratio (SNR). The SNR of SSVEP is fundamentally related to the characteristics of stimulus, such as its intensity and frequency, and it is also related to both the reference electrode and the active electrode. In the past, with SSVEP-based BCI, often the potential at ‘Cz’, the average potential at all electrodes or the average mastoid potential, were statically selected as the reference. In conjunction, a certain electrode in the occipital area was statically selected as the active electrode for all stimuli. This work proposed a dynamic selection method for the reference electrode, in which all electrodes can be looked upon as active electrodes, while an electrode which can result in the maximum sum relative-power of a specific frequency SSVEP can be confirmed dynamically and considered as the optimum reference electrode for that specific frequency stimulus. Comparing this dynamic selection method with previous methods, in which ‘Cz’, the average potential at all electrodes or the average mastoid potential were selected as the reference electrode, it is demonstrated that the SNR of SSVEP is improved significantly as is the accuracy of SSVEP detection.     

Measurement and monitoring of electrocardiogram belt tension in premature infants for assessment of respiratory function

Background  

Monitoring of the electrocardiogram (ECG) in premature infants with conventional adhesive-backed electrodes can harm their sensitive skin. Use of an electrode belt prevents skin irritation, but the effect of belt pressure on respiratory function is unknown. A strain gauge sensor is described which measures applied belt tension.     

织物电极的皮肤-电极接触阻抗测量方法分析

随着可穿戴式健康监测技术的发展,新型心电传感器-织物电极成为人们关注的热点,本文对织物电极的皮肤-电极接触阻抗测量方法进行了综述。首先介绍了织物电极的概念,分析了织物电极的皮肤-电极电化学界面、皮肤-电极电化学界面的等效电路和简化电路模型,得出了皮肤-电极接触阻抗的计算公式;其次,将皮肤-电极接触阻抗的测量方法归纳为直接测量法、参比测量法和模拟皮肤测量法三类,讨论了它们的测量原理和优缺点。本文认为需将模拟皮肤测量法和真实皮肤测量法有机结合,才能有效评价织物电极的阻抗特性,为织物电极的性能评价和心电信号采集电路的设计提供重要依据。最后,本文对织物电极待解决的问题进行了分析讨论。     

Cell-compatible array of three-dimensional tip electrodes for the detection of nitric oxide release

An array of electrodes on which cells could be grown directly was fabricated using silicon anisotropic etching and a thick-photoresist process and employed for the detection of nitric oxide (NO) released from a population of adherently growing human umbilical vein endothelial cells (HUVEC). The electrodes are tip-shaped and are 40 microm high of which only the top 15 microm are exposed Pt-tips. After electrochemical induced modification of the exposed Pt tips using Ni phthalocyanine the individual addressable electrode tips were sensitive and selective for the detection of NO at an applied constant potential of 750 mV. The silicon nitride insulation of the lower part of the tip electrodes prevented the death of the cells upon the application of the working potential at which NO was detected. It also helped to avoid the perturbation of the integrity of the sensing chemistry imparted on the electrode surface that could have resulted from the contact of the adherently growing cells with the active electrode surface. The release of nitric oxide from HUVEC was successfully monitored with different numbers of tip electrodes simultaneously connected as combined working electrode.     

Microelectrode Guided Implantation of Electrodes into the Subthalamic Nucleus of Rats for Long-term Deep Brain Stimulation

Deep brain stimulation (DBS) is a widely used and effective therapy for several neurologic disorders, such as idiopathic Parkinson’s disease, dystonia or tremor. DBS is based on the delivery of electrical stimuli to specific deep anatomic structures of the central nervous system. However, the mechanisms underlying the effect of DBS remain enigmatic. This has led to an interest in investigating the impact of DBS in animal models, especially in rats. As DBS is a long-term therapy, research should be focused on molecular-genetic changes of neural circuits that occur several weeks after DBS. Long-term DBS in rats is challenging because the rats move around in their cage, which causes problems in keeping in place the wire leading from the head of the animal to the stimulator. Furthermore, target structures for stimulation in the rat brain are small and therefore electrodes cannot easily be placed at the required position. Thus, a set-up for long-lasting stimulation of rats using platinum/iridium electrodes with an impedance of about 1 MΩ was developed for this study. An electrode with these specifications allows for not only adequate stimulation but also recording of deep brain structures to identify the target area for DBS. In our set-up, an electrode with a plug for the wire was embedded in dental cement with four anchoring screws secured onto the skull. The wire from the plug to the stimulator was protected by a stainless-steel spring. A swivel was connected to the circuit to prevent the wire from becoming tangled. Overall, this stimulation set-up offers a high degree of free mobility for the rat and enables the head plug, as well as the wire connection between the plug and the stimulator, to retain long-lasting strength.     

Coated Lithium Powder (CLiP) Electrodes for Lithium‐Metal Batteries

Safety issues caused by the metallic lithium inside a battery represent one of the main reasons for the lack of commercial availability of rechargeable lithium‐metal batteries. The advantage of anodes based on coated lithium powder (CLiP), compared to plain lithium foil, include the suppression of dendrite formation, as the local current density during stripping/plating is reduced due to the higher surface area. Another performance and safety advantage of lithium powder is the precisely controlled mass loading of the lithium anode during electrode preparation, giving the opportunity to avoid Li excess in the cell. As an additional benefit, the coating makes electrode manufacturing safer and eases handling. Here, electrodes based on coated lithium powder electrodes (CLiP) are introduced for application in lithium‐metal batteries. These electrodes are compared to lithium foil electrodes with respect to cycling stability, coulombic efficiency of lithium stripping/plating, overpotential, and morphology changes during cycling.