A novel flexible hydrogel electrode with a strong moisturizing ability for long-term EEG recording

Objective: A novel flexible hydrogel electrode with a strong moisturizing ability was prepared for long-term electroencephalography (EEG) monitoring. Approach: The hydrogel was synthesized by polymerizing the N-acryloyl glycinamide (NAGA) monomer. And a proper amount of glycerin was added to the hydrogel to increase the moisture retention ability of the electrodes. The hydrogel shows high mechanical properties, and the liquid in the hydrogel produces a hydrating effect on the skin stratum corneum, which could decrease the contact impedance between skin and electrode. In addition, the installation of hydrogel electrode is very convenient, and the skin of the subject does not need to be abraded. Main results: SEM images show that there are a large number of micropores in the hydrogel, which provide storage space for water molecules. The average potential drift of the hydrogel electrode is relatively low (1.974 ± 0.560 µV min-1). The average contact impedance of hydrogel electrode in forehead region and hair region are 6.43 ± 0.84 kΩ·cm2 and 13.15 ± 3.72 kΩ·cm2, respectively. The result of open/closed paradigm, steady-state visual evoked potentials (SSVEP), and P300 visual evoked potential show that hydrogel electrode has excellent performance. Compared with the hydrogel without glycerol, the moisture retention ability of hydrogel with glycerol was greatly improved. Significance. Compared with standard Ag/AgCl wet electrode, hydrogel electrode is more convenient to install and has strong moisture retention ability, which makes it have great potential in daily life for long-term EEG recording.

Non-invasive on-skin sensors for brain machine interfaces with epitaxial graphene

Brain-machine interfaces are key components for the development of hands-free, brain -controlled devices. Electroencephalogram (EEG) electrodes are particularly attractive for harvesting the neural signals in a non-invasive fashion. Here, we explore the use of epitaxial graphene grown on silicon carbide on silicon for detecting the electroencephalogram signals with high sensitivity. This dry and non-invasive approach exhibits a markedly improved skin contact impedance when benchmarked to commercial dry electrodes, as well as superior robustness, allowing prolonged and repeated use also in a highly saline environment. In addition, we report the newly -observed phenomenon of surface conditioning of the epitaxial graphene electrodes. The prolonged contact of the epitaxial graphene with the skin electrolytes functionalize the grain boundaries of the graphene, leading to the formation of a thin surface film of water through physisorption and consequently reducing its contact impedance by more than 75%. This effect is primed in highly saline environments, and could be also further tailored as pre-conditioning to enhance the performance and reliability of the epitaxial graphene sensors.

A System Identification and Implementation of a Soft Sensor for Freeform Bending

The primary goal of this study is the formulation of a soft sensor that predicts industrially relevant mechanical properties for freeform bending. This serves as the foundation of a closed-loop property control. It is hypothesized that by inline measurement of hardness, predictions regarding residual hoop stresses, local strength and strain level can be achieved. A novel hardness-based correlation scheme is introduced, which is implemented into an extended Kalman filter (EKF) and allows an inline prediction of local strength, residual hoop stresses and plasticity. Furthermore, the ultrasonic contact impedance (UCI) method is validated as a suitable inline measuring solution.

Ionic Liquid Regenerated Cellulose Membrane Electroless Plated By Silver Layer For ECG Signal Monitoring

Flexible electrodes have attracted the interest of a wide range of people because they can monitor human health signals like ECG, EMG and EEG as wearable devices. However, PDMS-based membrane electrodes have the problem of difficulty in depositing metal layers, while fabric electrodes have high contact impedance. Furthermore, the widely used Ag/AgCl electrodes have the shortcomings of skin inflammation or skin irritation. Therefore, we fabricate a skin-like electrical conductive electrode via electroless silver plating on the surface of regenerated cellulose membrane, in which the cellulose membrane is obtained by the dissolution of cotton fiber with green solvent ionic liquid [Bmim]Cl. The as-prepared biocompatible electrode with low skin-electrode contact impedance can be used as a dry electrode for a long-term period of use. The impedance at 700 Hz is only 8 kΩ/cm2, and the conductivity can reach 252 s/cm. After 5 hours of wear, the skin contact impedance of the electrode was only 10 kΩ/cm2 under 700 Hz(when AgNO3 was used at a concentration of 0.20 mol/L). Importantly, the electrodes not only provide a stable and clear ECG signal, but also offer a high level of comfort and low impedance, when used for long-term health monitoring.

Wearable Smart Textiles for Long-Term Electrocardiography Monitoring—A Review

The continuous and long-term measurement and monitoring of physiological signals such as electrocardiography (ECG) are very important for the early detection and treatment of heart disorders at an early stage prior to a serious condition occurring. The increasing demand for the continuous monitoring of the ECG signal needs the rapid development of wearable electronic technology. During wearable ECG monitoring, the electrodes are the main components that affect the signal quality and comfort of the user. This review assesses the application of textile electrodes for ECG monitoring from the fundamentals to the latest developments and prospects for their future fate. The fabrication techniques of textile electrodes and their performance in terms of skin–electrode contact impedance, motion artifacts and signal quality are also reviewed and discussed. Textile electrodes can be fabricated by integrating thin metal fiber during the manufacturing stage of textile products or by coating textiles with conductive materials like metal inks, carbon materials, or conductive polymers. The review also discusses how textile electrodes for ECG function via direct skin contact or via a non-contact capacitive coupling. Finally, the current intensive and promising research towards finding textile-based ECG electrodes with better comfort and signal quality in the fields of textile, material, medical and electrical engineering are presented as a perspective.

Internal and External Radiofrequency Assisted Lipo-Coagulation (RFAL) in the Control of Soft Tissue Contraction during Liposuction: Part 1 “Inside Out” Thermal Tissue Tightening

Radiofrequency Assisted Lipo-coagulation (RFAL) BodyTite is a contact, impedance, internal and external thermal regulation controlled, internal, minimally invasive, non-excisional procedure providing soft tissue lipo-coagulation and contraction that has been used for over 10 years to optimize skin and soft tissue contraction during liposuction procedures. The device deploys a bipolar applicator inserted into the liposuction zone. The internal, coated, electrode is positively charged and emits a coagulative, ablative injury that results in adipose liquification and Fibroseptal Network (FSN) contraction. The RF flows from the internal electrode after ablation and coagulation up to the external negatively charged return electrode moving on the skin, which heats and tightens the papillary dermis non-ablatively. The body areas that most benefit from this BodyTite technology and procedure include those areas most in need of non-excision contraction include the abdomen, upper arms, inner thighs, bra-line, neck and jaw line. Studies, show, that the combination of BodyTite internal thermal coagulation and external Morpheus8 (see Part 2) at the time of liposuction can result in 40–70% area skin contraction, greatly improving the soft tissue contours and Body shaping outcomes following lipo-contouring procedures.

Flexible Cellulose-Based Assembled with PEDOT: PSS Electrodes for ECG Monitoring

Electrocardiography is one of the most significant technologies for detecting cardiovascular diseases. Nowadays, the problems of various electrodes still meet a great challenge. Herein, we design a low cost, environmentally friendly and flexible conductive electrode using cellulose and polyvinyl alcohol as a substrate assembled with conductive polymer polythiophene by in-situ oxidative polymerization, and the green solvent 1-butyl-3-methylimidazolium chloride as a crosslinking agent. The polyvinyl alcohol/cellulose/PEDOT:PSS(PCPP) composite electrode has excellent features of flexibility, low skin contact impedance and comfortable contact with skin. When the load of EDOT reaches 15 wt%, the electrode is stable and can clearly monitor the characteristic wave of ECG signals. Therefore, based on cellulosic biopolymer and conductive polymer PEDOT:PSS, an environmentally friendly, flexible and stable PCPP composite electrode is obtained and can be a promising candidate applied in the fields of energy storage and ECG sensing.

Textile Electrodes: Influence of Knitting Construction and Pressure on the Contact Impedance

Textile electrodes, also called textrodes, for biosignal monitoring as well as electrostimulation are central for the emerging research field of smart textiles. However, so far, only the general suitability of textrodes for those areas was investigated, while the influencing parameters on the contact impedance related to the electrode construction and external factors remain rather unknown. Therefore, in this work, six different knitted electrodes, applied both wet and dry, were compared regarding the influence of specific knitting construction parameters on the three-electrode contact impedance measured on a human forearm. Additionally, the influence of applying pressure was investigated in a two-electrode setup using a water-based agar dummy. Further, simulation of an equivalent circuit was used for quantitative evaluation. Indications were found that the preferred electrode construction to achieve the lowest contact impedance includes a square shaped electrode, knitted with a high yarn density and, in the case of dry electrodes, an uneven surface topography consisting of loops, while in wet condition a smooth surface is favorable. Wet electrodes are showing a greatly reduced contact impedance and are therefore to be preferred over dry ones; however, opportunities are seen for improving the electrode performance of dry electrodes by applying pressure to the system, thereby avoiding disadvantages of wet electrodes with fluid administration, drying-out of the electrolyte, and discomfort arising from a “wet feeling”.