A novel functional electrical stimulation sleeve based on textile-embedded dry electrodes.

BACKGROUND: Functional electrical stimulation (FES) is a rehabilitation technique that enables functional improvements in patients with motor control impairments. This study presents an original design and prototyping method for a smart sleeve for FES applications. The article explains how to integrate a carbon-based dry electrode into a textile structure and ensure an electrical connection between the electrodes and the stimulator for effective delivery of the FES. It also describes the materials and the step-by-step manufacturing processes. RESULTS: The carbon-based dry electrode is integrated into the textile substrate by a thermal compression molding process on an embroidered conductive matrix. This matrix is composed of textile silver-plated conductive yarns and is linked to the stimulator. Besides ensuring the electrical connection, the matrix improves the fixation between the textile substrate and the electrode. The stimulation intensity, the perceived comfort and the muscle torque generated by the smart FES sleeve were compared to hydrogel electrodes. The results show a better average comfort and a higher average stimulation intensity with the smart FES sleeve, while there were no significant differences for the muscle torque generated. CONCLUSIONS: The integration of the proposed dry electrodes into a textile is a viable solution. The wearable FES system does not negatively impact the electrodes' performance, and tends to improve it. Additionally, the proposed prototyping method is applicable to an entire garment in order to target all muscles. Moreover, the process is feasible for industrial production and commercialization since all materials and processes used are already available on the market.

A dry polymer nanocomposite transcutaneous electrode for functional electrical stimulation.

BACKGROUND: Functional electrical stimulation (FES) can be used in rehabilitation to aid or improve function in people with paralysis. In clinical settings, it is common practice to use transcutaneous electrodes to apply the electrical stimulation, since they are non-invasive, and can be easily applied and repositioned as necessary. However, the current electrode options available for transcutaneous FES are limited and can have practical disadvantages, such as the need for a wet interface with the skin for better comfort and performance. Hence, we were motivated to develop a dry stimulation electrode which could perform equivalently or better than existing commercially available options. METHODS: We manufactured a thin-film dry polymer nanocomposite electrode, characterized it, and tested its performance for stimulation purposes with thirteen healthy individuals. We compared its functionality in terms of stimulation-induced muscle torque and comfort level against two other types of transcutaneous electrodes: self-adhesive hydrogel and carbon rubber. Each electrode type was also tested using three different stimulators and different intensity levels of stimulation. RESULTS: We found the proposed dry polymer nanocomposite electrode to be functional for stimulation, as there was no statistically significant difference between its performance to the other standard electrodes. Namely, the proposed dry electrode had comparable muscle torque generated and comfort level as the self-adhesive hydrogel and carbon rubber electrodes. From all combinations of electrode type and stimulators tested, the dry polymer nanocomposite electrode with the MyndSearch stimulator had the most comfortable average rating. CONCLUSIONS: The dry polymer nanocomposite electrode is a durable and flexible alternative to existing self-adhesive hydrogel and carbon rubber electrodes, which can be used without the addition of a wet interfacing agent (i.e., water or gel) to perform as well as the current electrodes used for stimulation purposes.

Development of an Aerogel-Based Wet Electrode for Functional Electrical Stimulation.

Functional electrical stimulation (FES) has been a useful therapeutic tool in rehabilitation, particularly for people with paralysis. To deliver stimulation in its most basic setup, a stimulator and at least a pair of electrodes are needed. The electrodes are an essential part of the system since they allow the transduction of the stimulator signals into the body. Their performance can influence the experience of both patient and therapist in terms of movement generation, comfort, and ease of use. For non-invasive surface stimulation, current electrode options have several limitations involving their interfacing with the skin, practical inconveniences, and short-term functionality. Standard hydrogel electrodes tend to lose their adhesion with the skin quickly, while dry or textile electrodes require constant wetting to be comfortable. In this paper, we present the fabrication, characterization, and FES testing of a new aerogel-based wet electrode for surface stimulation applications for long-term and reusable FES applications. We investigated its functionality by stimulating the biceps brachii of twelve healthy individuals and collected elbow joint torque and comfort ratings for three different intensity levels (low, moderate, and high) of FES. Comparing to standard hydrogel electrodes, no statistically significant difference was found for any intensity of stimulation in either torque or comfort. Overall, the new aerogel-based electrode has an appropriate impedance, is flexible and soft, is conformable to the skin, has a high water absorption and retention, and can be used for FES purposes.

Flexible, Thermally Stable, and Ultralightweight Polyimide-CNT Aerogel Composite Films for Energy Storage Applications.

Polyimide (PI) aerogels are promising in various fields of application, ranging from thermal insulators to aerospace. However, they are typically in the form of a bulk monolith, which suffers from a lack of conformability and drapability. Moreover, their electrical conductivity is limited, and they mainly display an insulative behavior. These shortcomings can limit the applications of PI aerogels in energy storage systems, which require ultralightweight flexible conductive films, which at the same time offer high thermal stability, ultralow density, and high surface area. To overcome these obstacles, the present study reports the fabrication of PI-carbon nanotube (PI-CNT) aerogel composite films with varying CNT content prepared through a sol-gel preparation method, followed by a supercritical drying procedure. Compared to pristine PI aerogels, which displayed a large shrinkage and density of 18.3% and 0.12 g cm-3, respectively, the incorporation of only 5 wt % CNTs resulted in a significant reduction of both shrinkage and density to only 11.5% and 0.10 g cm-3, respectively. This suggests the importance of CNTs in improving the dimensional stability of aerogels and creating a robust network. Further characterizations showed that incorporation of 5 wt % CNTs also resulted in the highest pore volume (1.25 cm3 g-1), highest surface area (324 m2 g-1), highest real permittivity (80), highest electrical conductivity (3 × 10-1 S m-1), and ultrahigh service temperature (575 °C). It was also shown that the aerogel films can withstand a large degree of bending, can be twisted, and can be fully rolled with no obvious cracks propagated in the structure. The combined outstanding properties of the developed aerogel composite films make them promising potential candidates for supercapacitor electrodes. Therefore, the electrochemical performance of the devices based on aerogel electrodes was further studied. The device demonstrated a high energy density of 2.6 Wh kg-1 at a power density of 303.8 W kg-1. The total capacitance after 5000 cycles was 91.8% of the initial capacitance, which indicated excellent stability and durability of the device. Overall, this work provides a facile yet effective methodology for the development of high-performance aerogel materials for energy storage applications.

Recent advances in tailoring and improving the properties of polyimide aerogels and their application.

With the rapid advancements in technology and growing aerospace applications, there is a need for effective low-weight and thermally insulating materials. Aerogels are known for their ultra-lightweight and they are highly porous materials with nanopores in a range of 2 to 50 nm with very low thermal conductivity values. However, due to hygroscopic nature and brittleness, aerogels are not used commercially and in daily life. To enhance the mechanical and hydrophobic properties, reinforcement materials such as styrene, cyanoacrylates, epoxy along with hydroxyl, amines, vinyl groups are added to the surface. The addition of organic materials resulted in lower service temperatures which reduce its potential applications. Polyimides (PI) are commonly used in engine applications due to their suitable stability at high temperatures along with excellent mechanical properties. Previous research on polyimide aerogels reported high flexibility or even foldability. However, those works' strategy was mainly limited to altering the backbone chemistry of polyimide aerogels by changing either the monomer's compositions or the chemical crosslinker. This work aims to summarize, categorize, and highlight the recent techniques for improving and tailoring properties of polyimide aerogels followed by the recent advancements in their applications.

Flexible, Air Dryable, and Fiber Modified Aerogel-Based Wet Electrode for Electrophysiological Monitoring.

This study presents a novel type of wet electrode material for electrophysiological monitoring based on a conductive aerogel film. The electrode material incorporates cellulose nanocrystal and fiber as a biocompatible polymer and multi-walled carbon nanotube as a conductive filler. The fabricated electrode is fully characterized to explore the chemical, mechanical, electrical, and water absorption properties. The wet aerogel film presents suitable mechanical flexibility owing to the use of fiber enabling it to be conformal to curved surfaces like human body. The water absorption percentage of the fabricated aerogel film is extremely high (∼500%) due to the porosity of the film and hydrophilicity of the base polymer allowing it for effective wet electrode applications. The film is air dryable with a fast (∼10 min) and facile wetting process granting the electrode application for long-term, multiple use, and remote monitoring of patients. The electrical impedance range of the fabricated aerogel electrodes is relatively low (20 Ω/cm2-370 Ω/cm2) which is within the range of use for various electrophysiological monitoring purposes such as electrocardiography (ECG) and electroencephalography (EEG). Overall, the presented study introduces a novel wet electrode based on porous and electrically conductive aerogel film to be used for various biomedical applications.

Polyimide aerogels with novel bimodal micro and nano porous structure assembly for airborne nano filtering applications.

Aerogels have presented a very high potential to be utilized as airborne nanoparticles' filtration media due to their nanoscale pore size and extremely high porosity. The filtering performance of aerogels, such as air permeability and filtration efficiency, is highly related to the configuration of aerogels' nanostructure assembly. However, as aerogel morphology is formed with respect to the intermolecular forces during the gelation stage, tailoring the aerogel nanostructure assembly is still a challenge. In this work, a novel strategy for tailoring polyimide aerogel nanostructure assembly is proposed by controlled disturbing of the intermolecular forces. From the results, the nanostructure assembly of the 4,4'-oxydianiline (ODA)-biphenyl-tetracarboxylic acid dianhydride (BPDA) polyimide aerogel is tailored to a uniform bimodal micro and nano porous structure. This was achieved by introducing the proper fraction of thermoplastic polyurethane (TPU) chains to the polyimide chains in the solution state and through a controlled process. The fabricated polyimide/TPU aerogels with bimodal morphology presented enhanced filtration performance, with 30% improved air permeability and reduced cell size of 3.51 nm over the conventional ODA-BPDA polyimide aerogels. Moreover, the fabricated bimodal aerogels present the reduced shrinkage, density, and effective thermal conductivity of 6.3% and 0.063 g cm-3, 28.7 mW m-1 K-1, respectively. Furthermore, the bimodal polyimide/TPU aerogels show the higher porosity of 96.5 vol% along with increased mechanical flexibility over the conventional polyimide aerogel with comparable backbone chemistry.

A High Performance Triboelectric Nanogenerator Using Porous Polyimide Aerogel Film.

This paper presents a novel aerogel-based Triboelectric Nanogenerator (TENG) which shows a superior performance for energy harvesting and sensing applications. Polyimide-based aerogel film with varying open-cell content level is developed to be used as the main contact material for the TENG. The fabricated aerogel film is fully characterized to reveal the chemical and mechanical properties of the developed material. It is shown the use of Polyimide aerogel film remarkably enhances the performance of the TENG compared to a TENG with fully dense Polyimide layer with no porosity. This enhancement is due to the increase on the effective surface area, charge generation inside the open-cells of the aerogel, and increase on the relative capacitance of the TENG device. The effect of varying porosity from zero to 70% of open-cell content reveals that the aerogel film with 50% shows the highest performance where the peak open-circuit voltage of 40V and peak short-circuit current of 5 µA are obtained. These values are higher than those of the TENG with simple Polyimide layer with an order of magnitude. Finally, the performance of proposed TENG under resistive loads and capacitors are tested. Thus, this work presents an effective method for high performance TENG.