A Nature-Inspired, Flexible Substrate Strategy for Future Wearable Electronics

Tannic acid - a bridge and suspending agent for lithium cobalt oxide and reduced graphene oxide: a lodestar for lithium-ion batteries

ABSTRACTLithium cobalt oxide (LCO) has been employed as cathode material for 40 years. However, the low solubility of LCOs in water and strong electrostatic force and H-bonding between the LCOs particles limited the use of the aqueous binders in the LCO system. We report a feasible and universal approach to fabricating a complex cathode of LCO and reduced graphene oxide (RGO). Tannic acid (TA) could simultaneously disperse LCO and RGO particles. Meanwhile, the branched polyphenol TA acts as a 'bridge' molecule for connecting the LCO and RGO, confirmed by the SEM test. The rheology properties of the PVDF slurry of cathode materials (LCO, LCO/, RGO, and TA/LCO/RGO) were also determined. It could be found that the TA could act as a crosslinking agent for the LCO and RGO particles, increasing the viscosity and storage modulus of the slurry. The cell employed the TA/LCO/RGO slurry as the cathode material, have a higher areal capacity, and had a higher redox potential than employed LCO/RGO and LCO as cathode materials, all of which could be attributed to the addition of the TA. This green molecule can be used to fabricate environmentally friendly and possibly biodegradable electrochemical energy storage devices.

Tannic acid ameliorates the hazards effect of beryllium induced neuro-alterations and oxidative stress in adult male rats

Background

Tannic acid (TA) is one of the most consumed and famous polyphenols with a widespread attention in the medical field according to its unique structural, pharmaceutical, physicochemical, antioxidant and other biological features. A rare study was conducted on the hazard effect of beryllium (Be) on the central nervous system.

Aims

This study aims to show the ability of beryllium to cross the blood brain barrier. Demonstrate the effect of beryllium and tannic acid separately or with each other on brain ions (Na+, K+, Ca++) and on norepinephrine, dopamine, serotonin, finally on the glutathione and malondialdehyde.

Animals grouping

Seventy-two rats were divided into four groups as control, Be, TA, and Be+TA where Be was injected intraperitoneally as 1 mg/Kg b. wt, TA was orally administrated as 5% in aquas solution.

Results

The administration of beryllium showed its ability to cross the blood brain barrier and accumulated in cortex > cerebellum>hypothalamus also, a significant increase in Na+, Ca++ cooperated with a significant decrease in K+ ions content was observed. Norepinephrine, dopamine, and serotonin showed a general significant decrease in their content joined with a significant decrease in glutathione (GSH) and elevation in malondialdehydes (MDA) because of Be intoxication. On the other hands the daily oral administration of tannic acid showed a general significant decrease in Na+, Ca++ ions content parallel with a significant increase K+ also, a non-significant change in the three measured neurotransmitters was noticed.

Conclusion

Tannic acid showed a mitigation effect against Be intoxication which may regarded to the tannic acid antioxidant, chelating effect.

Synthesis of Superelastic, Highly Conductive Graphene Aerogel/Liquid Metal Foam and its Piezoresistive Application

Graphene aerogel (GA) has important application potential as piezoresistive sensors due to its low density, high conductivity, high porosity, and good mechanical properties. However, the fabrication of GA-based sensors with good mechanical properties and excellent sensing performance is still challenging. Herein, liquid- metal-modified GAs (GA/LM) are proposed for the development of an excellent GA-based sensor. GA/LM with three-dimensional interconnected layered structure exhibits excellent compressive stress of 41 KPa and fast response time (<20 ms). While generally flexible GA composites cannot be compressed beyond 80 % strain without plastic deformation, GA/LM demonstrates a high compressive strength of 60 kPa under a strain of 90 %. A real-time pressure sensor was fabricated based on GA/LM-2 to monitor swallowing, pulse beating, finger, wrist and knee bending, and even plantar pressure during walking. These excellent features enable potential applications in health detection.

Flexible thin film thermocouples: From structure, material, fabrication to application

Flexible thin-film thermocouples (TFTCs) have been garnering interest as temperature sensors due to the advantages of being flexible, ultrathin, and ultralight. Additionally, they have fast response times and enable detection of temperature. These properties have made them suitable for applications such as wearable electronics, healthcare, portable personal devices, and smart detection systems. This review presents the progress in the development of flexible TFTCs. The mechanism, structural design, materials, fabrication methods, and related applications of flexible TFTCs are also elaborated. Finally, future development directions of flexible TFTCs are discussed such as wide-range temperature measurement, multiple sensor integration, and achieving reliable cold-end compensation systems.

Advances in Biodegradable Electronic Skin: Material Progress and Recent Applications in Sensing, Robotics, and Human-Machine Interfaces

The rapid growth of the electronics industry and proliferation of electronic materials and telecommunications technologies has led to the release of a massive amount of untreated electronic waste (e-waste) into the environment. Consequently, catastrophic environmental damage at the microbiome level and serious human health diseases threaten the natural fate of the planet. Currently, the demand for wearable electronics for applications in personalized medicine, electronic skins (e-skins), and health monitoring is substantial and growing. Therefore, "green" characteristics such as biodegradability, self-healing, and biocompatibility ensure the future application of wearable electronics and e-skins in biomedical engineering and bioanalytical sciences. Leveraging the biodegradability, sustainability, and biocompatibility of natural materials will dramatically influence the fabrication of environmentally friendly e-skins and wearable electronics. Here, the molecular and structural characteristics of biological skins and artificial e-skins are discussed. The focus then turns to the biodegradable materials, including natural and synthetic-polymer-based materials, and their recent applications in the development of biodegradable e-skin in wearable sensors, robotics, and human-machine interfaces (HMIs). Finally, the main challenges and outlook regarding the preparation and application of biodegradable e-skins are critically discussed in a near-future scenario, which is expected to lead to the next generation of biodegradable e-skins.

Elastic Fibers/Fabrics for Wearables and Bioelectronics

Wearables and bioelectronics rely on breathable interface devices with bioaffinity, biocompatibility, and smart functionality for interactions between beings and things and the surrounding environment. Elastic fibers/fabrics with mechanical adaptivity to various deformations and complex substrates, are promising to act as fillers, carriers, substrates, dressings, and scaffolds in the construction of biointerfaces for the human body, skins, organs, and plants, realizing functions such as energy exchange, sensing, perception, augmented virtuality, health monitoring, disease diagnosis, and intervention therapy. This review summarizes and highlights the latest breakthroughs of elastic fibers/fabrics for wearables and bioelectronics, aiming to offer insights into elasticity mechanisms, production methods, and electrical components integration strategies with fibers/fabrics, presenting a profile of elastic fibers/fabrics for energy management, sensors, e-skins, thermal management, personal protection, wound healing, biosensing, and drug delivery. The trans-disciplinary application of elastic fibers/fabrics from wearables to biomedicine provides important inspiration for technology transplantation and function integration to adapt different application systems. As a discussion platform, here the main challenges and possible solutions in the field are proposed, hopefully can provide guidance for promoting the development of elastic e-textiles in consideration of the trade-off between mechanical/electrical performance, industrial-scale production, diverse environmental adaptivity, and multiscenario on-spot applications.

Significantly Enhanced Electromagnetic Interference Shielding Performances of Epoxy Nanocomposites with Long-Range Aligned Lamellar Structures

High‑efficiency electromagnetic interference (EMI) shielding materials are of great importance for electronic equipment reliability, information security and human health. In this work, bidirectional aligned Ti₃C₂T_x@Fe₃O₄/CNF aerogels (BTFCA) were firstly assembled by bidirectional freezing and freeze-drying technique, and the BTFCA/epoxy nanocomposites with long-range aligned lamellar structures were then prepared by vacuum-assisted impregnation of epoxy resins. Benefitting from the successful construction of bidirectional aligned three-dimensional conductive networks and electromagnetic synergistic effect, when the mass fraction of Ti₃C₂T_x and Fe₃O₄ are 2.96 and 1.48 wt%, BTFCA/epoxy nanocomposites show outstanding EMI shielding effectiveness of 79 dB, about 10 times of that of blended Ti₃C₂T_x@Fe₃O₄/epoxy (8 dB) nanocomposites with the same loadings of Ti₃C₂T_x and Fe₃O₄. Meantime, the corresponding BTFCA/epoxy nanocomposites also present excellent thermal stability (T_{heat-resistance index} of 198.7 °C) and mechanical properties (storage modulus of 9902.1 MPa, Young's modulus of 4.51 GPa and hardness of 0.34 GPa). Our fabricated BTFCA/epoxy nanocomposites would greatly expand the applications of MXene and epoxy resins in the fields of information security, aerospace and weapon manufacturing, etc.

Tannic acid: a crosslinker leading to versatile functional polymeric networks: a review

With the thriving of mussel-inspired polyphenol chemistry as well as the demand for low-cost analogues to polydopamine in adhesive design, tannic acid has gradually become a research focus because of its wide availability, health benefits and special chemical properties. As a natural building block, tannic acid could be used as a crosslinker either supramolecularly or chemically, ensuring versatile functional polymeric networks for various applications. Up to now, a systematic summary on tannic-acid-based networks has still been waiting for an update and outlook. In this review, the common features of tannic acid are summarized in detail, followed by the introduction of covalent and non-covalent crosslinking methods leading to various tannic-acid-based materials. Moreover, recent progress in the application of tannic acid composites is also summarized, including bone regeneration, skin adhesives, wound dressings, drug loading and photothermal conversion. Above all, we also provide further prospects concerning tannic-acid-crosslinked materials.

A New Class of Electronic Devices Based on Flexible Porous Substrates

With the advent of the Internet of Things era, the connection between electronic devices and humans is getting closer and closer. New-concept electronic devices including e-skins, nanogenerators, brain-machine interfaces, and implantable medical devices, can work on or inside human bodies, calling for wearing comfort, super flexibility, biodegradability, and stability under complex deformations. However, conventional electronics based on metal and plastic substrates cannot effectively meet these new application requirements. Therefore, a series of advanced electronic devices based on flexible porous substrates (e.g., paper, fabric, electrospun nanofibers, wood, and elastic polymer sponge) is being developed to address these challenges by virtue of their superior biocompatibility, breathability, deformability, and robustness. The porous structure of these substrates can not only improve device performance but also enable new functions, but due to their wide variety, choosing the right porous substrate is crucial for preparing high-performance electronics for specific applications. Herein, the properties of different flexible porous substrates are summarized and their basic principles of design, manufacture, and use are highlighted. Subsequently, various functionalization methods of these porous substrates are briefly introduced and compared. Then, the latest advances in flexible porous substrate-based electronics are demonstrated. Finally, the remaining challenges and future directions are discussed.

Functionalized Fiber-Based Strain Sensors: Pathway to Next-Generation Wearable Electronics

Wearable strain sensors are arousing increasing research interests in recent years on account of their potentials in motion detection, personal and public healthcare, future entertainment, man-machine interaction, artificial intelligence, and so forth. Much research has focused on fiber-based sensors due to the appealing performance of fibers, including processing flexibility, wearing comfortability, outstanding lifetime and serviceability, low-cost and large-scale capacity. Herein, we review the latest advances in functionalization and device fabrication of fiber materials toward applications in fiber-based wearable strain sensors. We describe the approaches for preparing conductive fibers such as spinning, surface modification, and structural transformation. We also introduce the fabrication and sensing mechanisms of state-of-the-art sensors and analyze their merits and demerits. The applications toward motion detection, healthcare, man-machine interaction, future entertainment, and multifunctional sensing are summarized with typical examples. We finally critically analyze tough challenges and future remarks of fiber-based strain sensors, aiming to implement them in real applications.

Fiber Surface/Interfacial Engineering on Wearable Electronics

Surface/interfacial engineering is an essential technique to explore the fiber materials properties and fulfil new functionalities. An extensive scope of current physical and chemical treating methods is reviewed here together with a variety of real-world applications. Moreover, a new surface/interface engineering approach is also introduced: self-assembly via π-π stacking, which has great potential for the surface modification of fiber materials due to its nondestructive working principle. A new fiber family member, metal-oxide framework (MOF) fiber shows promising candidacy for fiber based wearable electronics. The understanding of surface/interfacial engineering techniques on fiber materials is advanced here and it is expected to guide the rational design of future fiber based wearable electronics.

Ionic Conductive Organohydrogel With Ultrastretchability, Self-Healable and Freezing-Tolerant Properties for Wearable Strain Sensor

Currently, stretchable hydrogel has attracted great attention in the field of wearable flexible sensors. However, fabricating flexible hydrogel sensor simultaneously with superstretchability, high mechanical strength, remarkable self-healing ability, excellent anti-freezing and sensing features via a facile method remains a huge challenge. Herein, a fully physically linked poly(hydroxyethyl acrylamide)-gelatin-glycerol-lithium chloride (PHEAA-GE-Gl-LiCl) double network organohydrogel is prepared via a simple one-pot heating-cooling-photopolymerization method. The prepared PHEAA-GE-Gl-LiCl organohydrogel exhibits favorable stretchability (970%) and remarkable self-healing property. Meanwhile, due to the presence of glycerol and LiCl, the PHEAA-GE-Gl-LiCl organohydrogel possesses outstanding anti-freezing capability, it can maintain excellent stretchability (608%) and conductivity (0.102 S/m) even at -40°C. In addition, the PHEAA-GE-Gl-LiCl organohydrogel-based strain sensor is capable of repeatedly and stably detecting and monitoring both large-scale human motions and subtle physiological signals in a wide temperature range (from -40°C to 25°C). More importantly, the PHEAA-GE-Gl-LiCl organohydrogel-based sensor displays excellent strain sensitivity (GF = 13.16 at 500% strain), fast response time (300 ms), and outstanding repeatability. Based on these super characteristics, it is envisioned that PHEAA-GE-Gl-LiCl organohydrogel holds promising potentials as wearable strain sensor.

Wearable E-Textiles Using a Textile-Centric Design Approach

Electronics worn on the body have the potential to improve human health and the quality of life by monitoring vital signs and movements, displaying information, providing self-illumination for safety, and even providing new routes for personal expression through fashion. Textiles are a part of daily life in clothing, making them an ideal platform for wearable electronics. The acceptance of wearable e-textiles hinges on maintaining the properties of textiles that make them compatible with the human body. Beneficial properties such as softness, stretchability, drapability, and breathability come from the 3D fibrous structures of knitted and woven textiles. However, these structures also present considerable challenges for the fabrication of wearable e-textiles. Fabrication methods used for modern electronic devices are designed for 2D planar substrates and are mostly unsuitable for the complex 3D structures of textiles. There is thus an urgent need to develop fabrication methods specifically for e-textiles to advance wearable electronics. Solution-based fabrication methods are a promising approach to fabricating wearable e-textiles, especially considering that textiles have been successfully modified using pigmented dyes in dyebaths and printing inks for thousands of years. In this Account, we discuss our research on the solution-based electroless metallization of textiles to fabricate conductive e-textiles that are building blocks for e-textile devices. Electroless metallization solutions fully permeate textile structures to deposit metallic coatings on the surfaces of individual textile fibers, maintaining the inherent textile structures and wearability. The resulting e-textiles are highly conductive, soft, and stretchable. We furthermore discuss ways to turn the challenges related to textile structures into new opportunities by strategically using the structural features of textiles for e-textile device design. We demonstrate this textile-centric approach to designing e-textile devices using two examples. We discuss how the structure of an ultrasheer knitted textile forms a useful framework for new e-textile transparent conductive electrodes and describe the implementation of these electrodes to form highly stretchable light-emitting e-textiles. We also show how the structural features of velour fabrics form the basis for an innovative "island-bridge" strain-engineering structure that enables the integration of brittle electroactive materials and protects them from strain-induced damage, leading to the fabrication of stretchable textile-based lithium-ion battery electrodes. With the vast variety of textile structures available, we highlight the opportunities associated with this textile-centric design approach to advance textile-based wearable electronics. Such advances depend on a deep understanding of the relationship between the textile structure and the device requirements, which may potentially lead to the development of new textile structures customized to support specific devices. We conclude with a discussion of the challenges that remain for the future of e-textiles, including durability, sustainability, and the development of performance standards.

Fully Soft Pressure Sensor Based on Bionic Spine-Pillar Structure for Robotics Motion Monitoring

Soft and stretchable sensors are essential to the development of electronic skin, especially their potential applications in health care and intelligent robots, which have increasingly attracted attentions. Herein, inspired by the epidermal tissue hierarchy, we propose a high-sensitivity fully soft capacitive pressure sensor with bionic spine-pillar microstructure. Benefiting from the combination of the random microscale spines and the millimeter-sized pillar array prepared based on polydimethylsiloxane, the proposed sensor exhibits a well deformability, a high sensitivity up to 2.87 k/Pa at low-pressure range, and a broad linear pressure dynamic range from 5 Pa to 100 kPa. A simple equivalent circuit model was established to demonstrate the sensing mechanism and geometric effect. For practical application demonstrations, the sensor was utilized to monitor local subtle and large movements of the skin, such as finger bending, wrist bending, swallowing, and facial muscle movements. The sensor shows a conformality with human skin to follow the skin extension closely. Furthermore, the proposed sensing strategy can provide a distinguishable tactile feedback for controlling robot arm and soft claw in various tasks, illustrating its potential applications in robotics.

A Highly Controlled Organic-Inorganic Encapsulation Nanocomposite with Versatile Features toward Wearable Device Applications

Ultraviolet-curable polyurethane acrylate (PUA) materials can be used in a number of important applications spanning from microfluidics, surface patterning to wearable technology. For the first time, the potential of encapsulation of modified zirconia (ZrO₂ ) nanoparticles is reported in PUA-based hybrid films aimed to facilitate profoundly enhanced hardness and refractive index. By successfully manipulating the interfacial reaction conditions between ZrO₂ nanoparticles and PUA film, the PUA-based nanocomposites exhibit an ultrahigh hardness of 9 and superior refractive index of 1.64 (589.3 nm). The outcomes obtained pave the way for seamless application of nanozirconia/PUA as a potent encapsulating material that provides structurally morphable, water resistant, and optically transparent light emitting diodes toward wearables devices in healthcare.

Red wine-inspired tannic acid-KH561 copolymer: its adhesive properties and its application in wound healing

Damaged tissue with an open wound is one of the daily injuries and can have different levels of severity. Inspired by the textile dyeing, coloration and skin care effect of pyrogallol-rich red wine, tannic acid-KH561 (TA561) copolymer was fabricated by phenol-silanol reaction and polycondensation of silane in an aqueous medium under mild conditions. This copolymer could undergo sol-gel transition via continuous heating or when simply placed at room temperature, during which liquid TA561 oligomers connected with each other to form solid TA561 as a bulk resin or thin film. Combining the advantages of the polyphenols and polysiloxane, TA561 can be used as an adhesive for multiple surfaces, including wood, polytetrafluoroethylene, poly(vinyl chloride), aluminum chips and silicon rubber. Furthermore, TA561 also possessed reducing activity towards Ag+ or Au3+ ions to form the corresponding nanoparticles. An in vivo antimicrobial ability test indicated that TA561 could promote wound healing and showed resistance to methicillin-resistant Staphylococcus aureus (MRSA) infection in comparison with KH561. Indeed, TA561 has the potential to be utilized as a low-cost, green bioadhesive material for skin preparations.

Conducting materials as building blocks for electronic textiles

ABSTRACT

To realize the full gamut of functions that are envisaged for electronic textiles (e-textiles) a range of semiconducting, conducting and electrochemically active materials are needed. This article will discuss how metals, conducting polymers, carbon nanotubes, and two-dimensional (2D) materials, including graphene and MXenes, can be used in concert to create e-textile materials, from fibers and yarns to patterned fabrics. Many of the most promising architectures utilize several classes of materials (e.g., elastic fibers composed of a conducting material and a stretchable polymer, or textile devices constructed with conducting polymers or 2D materials and metal electrodes). While an increasing number of materials and devices display a promising degree of wash and wear resistance, sustainability aspects of e-textiles will require greater attention.

Ultraelastic Yarns from Curcumin-Assisted ELD toward Wearable Human-Machine Interface Textiles

Intelligent human-machine interfaces (HMIs) integrated wearable electronics are essential to promote the Internet of Things (IoT). Herein, a curcumin-assisted electroless deposition technology is developed for the first time to achieve stretchable strain sensing yarns (SSSYs) with high conductivity (0.2 Ω cm-1) and ultralight weight (1.5 mg cm-1). The isotropically deposited structural yarns can bear high uniaxial elongation (>>1100%) and still retain low resistivity after 5000 continuous stretching-releasing cycles under 50% strain. Apart from the high flexibility enabled by helical loaded structure, a precise strain sensing function can be facilitated under external forces with metal-coated conductive layers. Based on the mechanics analysis, the strain sensing responses are scaled with the dependences on structural variables and show good agreements with the experimental results. The application of interfacial enhanced yarns as wearable logic HMIs to remotely control the robotic hand and manipulate the color switching of light on the basis of gesture recognition is demonstrated. It is hoped that the SSSYs strategy can shed an extra light in future HMIs development and incoming IoT and artificial intelligence technologies.

Hybrid Metallic Foam with Superior Elasticity, High Electrical Conductivity, and Pressure Sensitivity

Growing interest has been received in metallic foams for their combined features of metals and porous structures. Coating metals on polymers have been the most prevalent method to fabricate hybrid metallic foams to inherit both the merits of metals and the mechanical flexibility of polymers. However, direct coating metals on foams is challenging and requires tedious synthesis, such as electrolysis and chemical reduction. This work reported a facile strategy to build hybrid metallic foams via in situ foaming of liquid metals (LM) and polyurethane. The fluidity and incompatibility of LM with porous polyurethane allow the coating of LM on polymers. LM-Foams exhibit high electrical conductivity (3.9 × 10⁴ S/m), low density (ρ < 1 g/cm³), phenomenal elasticity (recover at 95% strain), and excellent mechanical stability (stable with 1000 compressive cycles). Interestingly, the ease of deformation for fluidic fillers in elastic polyurethane generates additional resistive change under pressure, showing unique sensory behaviors which were not observed in conventional conductive foams, such as high response sensitivity (gauge factor >25), short response time (202 ms), and outstanding electrical stability. The nonuniform size distribution of pores leads LM-Foams to show unusual position-dependent sensitivity, enabling advanced applications as password pads and electrical protection foams.

3D Shapeable, Superior Electrically Conductive Cellulose Nanofibers/Ti3C2Tx MXene Aerogels/Epoxy Nanocomposites for Promising EMI Shielding

In this work, 3D highly electrically conductive cellulose nanofibers (CNF)/Ti₃C₂T_x MXene aerogels (CTA) with aligned porous structures are fabricated by directional freezing followed by freeze-drying technique, and the thermally annealed CTA (TCTA)/epoxy nanocomposites are then fabricated by thermal annealing of CTA, subsequent vacuum-assisted impregnation and curing method. Results show that TCTA/epoxy nanocomposites possess 3D highly conductive networks with ultralow percolation threshold of 0.20 vol% Ti₃C₂T_x. When the volume fraction of Ti₃C₂T_x is 1.38 vol%, the electrical conductivity (σ), electromagnetic interference shielding effectiveness (EMI SE), and SE divided by thickness (SE/d) values of the TCTA/epoxy nanocomposites reach 1672 S m^-1, 74 dB, and 37 dB mm^-1, respectively, which are almost the highest values compared to those of polymer nanocomposites reported previously at the same filler content. In addition, compared to those of the samples without Ti₃C₂T_x, the storage modulus and heat-resistance index of TCTA/epoxy nanocomposites are enhanced to 9792.5 MPa and 310.7°C, increased by 62% and 6.9°C, respectively, presenting outstanding mechanical properties and thermal stabilities. The fabricated lightweight, easy-to-process, and shapeable TCTA/epoxy nanocomposites with superior EMI SE values, excellent mechanical properties, and thermal stabilities greatly broaden the applications of MXene-based polymer composites in the field of EMI shielding.

Flexible Ultrasonic Transducer Array with Bulk PZT for Adjuvant Treatment of Bone Injury

Flexible electronic devices are developing rapidly, especially in medical applications. This paper reports an arrayed flexible piezoelectric micromachined ultrasonic transducer (FPMUT) with a sandwich structure for adjuvant treatment of bone injury. To make the device conformable and stretchable for attaching to the skin surface, the flexible substrate of polydimethylsiloxane (PDMS) was combined with the flexible metal line interconnection between the bulk lead zirconate titanate (PZT) arrays. Simulations and experiments were carried out to verify the resonant frequency and tensile property of the reported FPMUT device. The device had a resonant frequency of 321.15 KHz and a maximum sound pressure level (SPL) of 180.19 dB at the distance of 5 cm in water. In addition, detailed experiments were carried out to test its acoustic performance with different pork tissues, and the results indicated good ultrasound penetration. These findings confirm that the FPMUT shows unique advantages for adjuvant treatment of bone injury.