The Rising Aerogel Fibers: Status, Challenges, and Opportunities

Review on the application of biomass-based aerogels in the field of thermal insulation

The continuous progression of industrialisation and the burgeoning global population have precipitated the non-renewable energy crisis and exacerbated environmental problems, thereby stimulating a huge demand for production of environmentally friendly materials. Typically, biomass-based aerogels (BAs) derived from cellulose, chitosan (CS), lignin, and alginate have been gradually captivating the attention of researchers owing to their high specific surface area, substantial porosity, low density, porous architecture, and biodegradability. In this review, we demonstrate the sustainability of BAs by contrasting the overall advantages or disadvantages of BAs with those of synthetic alternatives in terms of cost, insulation performance, and planetary boundaries. In addition, the aerogels based on biomass in recent years are summarized, including thermal insulation mechanisms, the raw materials, test methods, preparation approaches (focusing on the use of crosslinking and drying methods in the preparation process), as well as the wide-ranging applications. Furthermore, we offer the incisive insights into the challenges and prospective opportunities for BAs. The up-to-date summary and discussion will be beneficial to the development of functional BAs, which can improve resource utilization efficiency, thereby catalyzing the advancement of green technology.

Anti-Fatigue Cellular Graphene Aerogel Through Multiscale Joint Strengthening

Despite fatigue free of monolayer graphene, its assemblies, like cellular graphene aerogels (CGA), are usually suffering of frequent fatigue and inherent strength degradation in repeated loading. In this work, by employing multiscale modeling, the highly intrinsic anisotropic mechanical properties of the cell wall due to the layer-by-layer stacked graphene sheets are uncovered, which easily trigger the unique skeleton joints damage during repeated loading and contribute the primary fatigue mechanism of CGA. Conversely, multiscale joint strengthening strategies are proposed by interlayer crosslinking and joint curvation, improving the interlayer interaction, and decreasing interlayer stress during compression, respectively, so as to effectively suppress joint damage to improve fatigue performance of CGA. This work not only clarifies the underlying fatigue mechanism of 2D cellular materials but also highlights optimal design strategies for developing anti-fatigue graphene cellular structures.

Air-Drying for Rapid Manufacture of Flexible Aramid Nanofiber Aerogel Fibers with Robust Mechanical Properties and Thermal Insulation in Harsh Environments

Aerogel fibers uniting characteristics of both aerogels (lightweight and porosity) and fibers (flexibility and wearability) exhibit a great potential for the production of the next generation of thermal protection textiles; still, the complex drying procedures and mechanical brittleness remain the main obstacles toward further exploitation. Herein, flexible and robust aramid nanofiber aerogel fibers (ANAFs) are scalably prepared by continuous wet-spinning coupled with fast air-drying. This synthesis involves calcium ions (Ca2⁺) cross-linking and solvent displacement by low surface tension solvents, to enhance skeleton strength and reduce the capillary force during evaporation, respectively, thus minimizing shrinkage to 29.0% and maximizing specific surface area to 225.0 m2 g-1 for ANAF. Surprisingly, the air-dried ANAF showed excellent tensile strength (13.5 MPa) and toughness (7.0 MJ m-3), allowing their easy weaving into the textile without damage. Importantly, the ANAF textile with a skin-core porous structure exhibited low thermal conductivity (≈38.5 mW m-1 K-1) and excellent thermal insulation ability in the wide temperature range (-196 to 400 °C). Besides, the aramid molecular structure, as well as Ca2⁺ cross-linking, endowed the ANAF with high thermal stability and flame retardancy. Consequently, the robust ANAF with a fast-air-drying method is promising for thermal protection in extreme environments, such as in spacesuits.

Adhesion Strategy for Cross-Linking AgNWs/MXene Janus Membrane: Stretchable and Self-Healing Electromagnetic Shielding and Infrared Stealth Capabilities

Developing lightweight polymer shielding membranes with additional physicochemical properties is of great significance for addressing the complex contemporary security demands. However, precise structural design at the molecular level remains a challenge. Herein, a unique Janus composite membrane is assembled from conductive AgNWs/MXene 1D/2D network and polyurethane elastomer (MPHEA), displaying combined superior electromagnetic shielding effectiveness (EMSE) of up to 80 dB and remarkable infrared stealth capability at a wide temperature range of room temperature to 50 °C. Moreover, the endowed chemical crosslinking in the membrane resulted in the exceptional mechanical strength, self-healing, and superior adhesion. The maintained electromagnetic shielding (over 20 dB) even under a strain of 40% and the recovered shielding efficiency of 90% after mechanical damage and self-healing are observed, which is attributed to the synergistic 3D polymer elastic and 1D/2D conductive network in the multi-dimensional crosslinked MPHEA@AgNWs/MXene composite membrane. This work has represented an excellent micro-nano structure design strategy on multifunctional electromagnetic wave manager in complex application scenario.

A Review on MXene/Nanocellulose Composites: Toward Wearable Multifunctional Electromagnetic Interference Shielding Application

With the rapid development of mobile communication technology and wearable electronic devices, the electromagnetic radiation generated by high-frequency information exchange inevitably threatens human health, so high-performance wearable electromagnetic interference (EMI) shielding materials are urgently needed. The 2D nanomaterial MXene exhibits superior EMI shielding performance owing to its high conductivity, however, its mechanical properties are limited due to the high porosity between MXene nanosheets. In recent years, it has been reported that by introducing natural nanocellulose as an organic framework, the EMI shielding and mechanical properties of MXene/nanocellulose composites can be synergically improved, which are expected to be widely used in wearable multifunctional shielding devices. In this review, the electromagnetic wave (EMW) attenuation mechanism of EMI shielding materials is briefly introduced, and the latest progress of MXene/nanocellulose composites in wearable multifunctional EMI shielding applications is comprehensively reviewed, wherein the advantages and disadvantages of different preparation methods and various types of composites are summarized. Finally, the challenges and perspectives are discussed, regarding the performance improvement, the performance control mechanism, and the large-scale production of MXene/nanocellulose composites. This review can provide guidance on the design of flexible MXene/nanocellulose composites for multifunctional electromagnetic protection applications in the future intelligent wearable field.

Super-strong hydrogel reinforced by an interconnected hollow microfiber network via regulating the water-cellulose-copolymer interplay

The discontinuous fiber reinforced hydrogels are easy to fail due to the fracture of the fiber matrix during load-bearing. Here, we propose a novel strategy based on the synergistic reinforcement of interconnected natural fiber networks at multiple scales to fabricate hydrogels with extraordinary mechanical properties. Specifically, the P(AA-AM)/Cel (P(AA-AM), poly(acrylic acid-acrylamide); Cel, cellulose) hydrogel is synthesized by copolymerizing AA and AM on a substrate of paper with an interconnected hollow cellulose microfiber network. This innovative design achieves a collaborative improvement of mechanical properties, including a 253-times increase in strength (27.8 vs. 0.11 MPa), 137-times increase in work of fracture (3.59 vs. 0.026 MJ m-3), and 235-times increase in fracture energy (16.48 vs. 0.07 kJ m-2). These outstanding mechanical properties benefit from the P(AA-AM) network formed by the copolymerization, which fills both the inside and outside of the hollow cellulose fibers, thus establishing abundant strong hydrogen bonds with the fibers and welding the fiber junctions. Consequently, the hydrogel exhibits enhanced resistance to the slippage and fracture of fibers. This strategy demonstrates the mechanical strengthening effectiveness of a variety of hydrogels by regulating the water-cellulose-copolymer interplay, representing a practical and universal route for designing super-strong hydrogels.

Biopolymer-Based Flame Retardants and Flame-Retardant Materials

Polymeric materials featuring excellent flame retardancy are essential for applications requiring high levels of fire safety, while those based on biopolymers are highly favored due to their eco-friendly nature, sustainable characteristics, and abundant availability. This review first outlines the pyrolysis behaviors of biopolymers, with particular emphasis on naturally occurring ones derived from non-food sources such as cellulose, chitin/chitosan, alginate, and lignin. Then, the strategies for chemical modifications of biopolymers for flame-retardant purposes through covalent, ionic, and coordination bonds are presented and compared. The emphasis is placed on advanced methods for introducing biopolymer-based flame retardants into polymeric matrices and fabricating biopolymer-based flame-retardant materials. Finally, the challenges for sustaining the current momentum in the utilization of biopolymers for flame-retardant purposes are further discussed.

Fire-Safe Aerogels and Foams for Thermal Insulation: From Materials to Properties

The ambition of human beings to create a comfortable environment for work and life in a sustainable way has triggered a great need for advanced thermal insulation materials in past decades. Aerogels and foams present great prospects as thermal insulators owing to their low density, good thermal insulation, mechanical robustness, and even high fire resistance. These merits make them suitable for many real-world applications, such as energy-saving building materials, thermally protective materials in aircrafts and battery, and warming fabrics. Despite great advances, to date there remains a lack of a comprehensive yet critical review on the thermal insulation materials. Herein, recent progresses in fire-safe thermal-insulating aerogels and foams are summarized, and pros/cons of three major categories of aerogels/foams (inorganic, organic and their hybrids) are discussed. Finally, key challenges associated with existing aerogels are discussed and some future opportunities are proposed. This review is expected to expedite the development of advanced aerogels and foams as fire-safe thermally insulating materials, and to help create a sustainable, safe, and energy-efficient society.

Tough and thermal insulating cellulose-based aerogel fiber via long yarn-assisted interfacial polyelectrolyte complexation spinning

Cellulose-based aerogel fibers are recognized as a promising candidate for wearable thermal insulation textiles due to their high porosity, extremely low thermal conductivity, and environmental friendliness. Unfortunately, their practical application in textiles is severely limited by their brittleness. Herein, a novel "long yarn-assisted interfacial polyelectrolyte complexation (YAIPC) spinning" technique is proposed to fabricate cellulose-based aerogel fibers with a unique core-shell structure. The as-prepared core-shell aerogel fibers show excellent thermal insulation performance (34.3 mW m-1 K-1) and robust mechanical strength (∼100 MPa, 31.5 MJ m-3), providing great potential as wearable thermal insulating materials. Accordingly, our research would open a new avenue for designing and constructing wearable aerogel fibers and textiles.

Bio-Templated Aerogel Fibers: Heterogeneous Spinodal Architecting and In Situ Fibrillation of Thermoplastic Polyurethane-Silica on Nanostructured Cellulose Nanofiber Scaffold for Enhanced Thermomechanical Performance

This study addresses the inherent fragility and fractal limitations of traditional silica aerogels by developing a bio-templated aerogel fiber. Integrating cellulose nanofibers (CNFs), thermoplastic polyurethane (TPU), and silica aerogel (SA) in a dimethyl sulfoxide (DMSO) dispersion, a gel-spinning technique was employed to create aerogel fibers with superior thermomechanical performance. CNF also provided excellent rheological modification for successful spinnability, fast gelation, and fiber formation. The unique hierarchical structure of these fibers, formed through hot-stretching and surface modification, combined the superior mechanical strength and flexibility of TPU with the exceptional insulation properties of CNF and SA. The CNF network, encapsulated within the SA particles, formed a core-shell structure, axially aligned, that significantly enhances the thermal stability and mechanical performance of the fibers while maintaining a lightweight and porous architecture. Comprehensive morphological, thermal, and mechanical analyses were conducted to evaluate the properties of the developed aerogel fibers. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy verified the successful surface modification and grafting reactions on CNF, contributing to improved hydrophobicity and thermal insulation. Adjusting the CNF content allowed for tailoring of the thermomechanical characteristics, with a notable 294% increase in tensile strength from 5.3 to 15.6 MPa and an enhanced crystallization temperature from 106 to 119.97 °C. Furthermore, cyclic tensile and compression tests validated the durability and shape recovery capabilities of the aerogel fibers, making them promising candidates for high-performance applications in extreme environments. The thermal conductivity validated by experimental data further highlights the potential of CNF-based aerogel fibers as sustainable and multifunctional materials for advanced thermal insulation, mechanical reinforcement, and flexible structural applications.

Polyimide Aerogel Fiber Bundles for Extreme Thermal Management Systems in Aerospace Applications

Aerogel fibers are an emerging class of ultralightweight materials, which, compared to conventional bulk monolithic and aerogel films, provide better flexibility and extensibility. Despite the recent advancements in this field, due to their highly porous structure, their mechanical properties can be deteriorated. Inspired by the textile industry, we report the development of aerogel fiber bundles with twisted structures as a promising strategy to enhance the mechanical performance and practicality of aerogel fibers. Polyimide (PI) aerogel fibers were prepared via the sol-gel confined transition method. The fibers showed a unique nanostructured assembly with high specific surface area, excellent optical transparency, outstanding flexibility at diverse extreme conditions, self-extinguishing behavior, and superior thermal insulation performance. Using PI aerogel fibers as the backbone, aerogel fiber bundles in various configurations were designed and fabricated. A systematic study was performed to analyze the effect of design parameters on the mechanical performance of the bundles. Results revealed an optimal twist level for bundles, leading to a peak in mechanical properties across various bundle configurations. The observed improvement in mechanical properties was attributed to increased fiber-to-fiber binding strength, enhanced friction, and interlocking mechanism of fibers, underscoring the potential of the optimized twist level for enhancing the performance of aerogel fiber bundles. Overall, the development of aerogel fiber bundles holds great promise in revolutionizing the production of high-performance ultralightweight materials for thermal management applications.

HNTs Improve Flame Retardant and Thermal Insulation of the PVA/CA Composite Aerogel

Porous materials are widely used in construction, batteries, electrical appliances, and other fields. In order to meet the demand for flame-retardant and thermal insulation properties of organic porous materials, in this work, poly(vinyl alcohol)/calcium alginate/halloysite nanotube (PVA/CA/HNTs) aerogels with a hierarchical pore structure at micrometer-nanometer scales were prepared through freeze-drying using PVA as the substrate. The cross-linking reactions of PVA with H3BO3 and sodium alginate (SA) with CaCl2 constructed a double cross-linking network structure within the aerogel. And the HNTs were incorporated as reinforcing agents. The experimental results showed that the PVA/CA/HNTs aerogels had excellent flame-retardant and thermal insulation properties, and the heat release rate (HRR) and total heat release (THR) were effectively reduced compared to the PVA/CA aerogel. In addition, PVA/CA/HNTs aerogels had a high limiting oxygen index (LOI 60%) and low thermal conductivity (0.040 W/m·K). While their surface was subjected to a flame (800-1000 °C) for 25 min, the temperatures of the back surface were still lower than 80 °C. The low thermal conductivity of HNTs with hollow nanotube-like structures and the excellent flame-retardant properties of CA contributed to this phenomenon. The presence of HNTs and CA facilitated the formation of a dense carbon layer during combustion, enhancing the flame retardancy for PVA. In addition, the interpenetrating cross-linking network and the unique nanopores of HNTs collectively established a hierarchical pore structure within the gel, effectively impeding substance and heat exchange between the substrate and external environment. As the flame-retardant and thermal insulating material, PVA/CA/HNTs aerogels have a promising development prospect and potential in the fields of construction, transportation, electronics, and electrical appliances.

Ultrathin aerogel-structured micro/nanofiber metafabric via dual air-gelation synthesis for self-sustainable heating

Incorporating passive heating structures into personal thermal management technologies could effectively mitigate the escalating energy crisis. However, current passive heating materials struggle to balance thickness and insulating capability, resulting in compromised comfort, space efficiency, and limited thermoregulatory performance. Here, a dual air-gelation strategy, is developed to directly synthesize ultrathin and self-sustainable heating metafabric with 3D dual-network structure during electrospinning. Controlling the interactions among polymer, solvent, and water enables the microphase separation of charged jets, while adjusting the distribution of carbon black nanoparticles within charged fluids to form fibrous networks composed of interlaced aerogel micro/nanofibers with heat storage capabilities. With a low thickness of 0.18 mm, the integrated metafabric exhibits exceptional thermal insulation performance (15.8 mW m-1K-1), superhydrophobicity, enhanced mechanical properties, and high breathability while maintaining self-sustainable radiative heating ability (long-lasting warming of 8.8 °C). This strategy provides rich possibilities to develop advanced fibrous materials for smart textiles and thermal management.

Preparation of Fibrous Three-Dimensional Porous Materials and Their Research Progress in the Field of Stealth Protection

Intelligent and diversified development of modern detection technology greatly affects the battlefield survivability of military targets, especially infrared, acoustic wave, and radar detection expose targets by capturing their unavoidable infrared radiation, acoustic wave, and electromagnetic wave information, greatly affecting their battlefield survival and penetration capabilities. Therefore, there is an urgent need to develop stealth-protective materials that can suppress infrared radiation, reduce acoustic characteristics, and weaken electromagnetic signals. Fibrous three-dimensional porous materials, with their high porosity, excellent structural adjustability, and superior mechanical properties, possess strong potential for development in the field of stealth protection. This article introduced and reviewed the characteristics and development process of fibrous three-dimensional porous materials at both the micrometer and nanometer scales. Then, the process and characteristics of preparing fibrous three-dimensional porous materials through vacuum forming, gel solidification, freeze-casting, and impregnation stacking methods were analyzed and discussed. Meanwhile, their current application status in infrared, acoustic wave, and radar stealth fields was summarized and their existing problems and development trends in these areas from the perspectives of preparation processes and applicability were analyzed. Finally, several prospects for the current challenges faced by fibrous three-dimensional porous materials were proposed as follows: functionally modifying fibers to enhance their applicability through self-cross-linking; establishing theoretical models for the transmission of thermal energy, acoustic waves, and electromagnetic waves within fibrous porous materials; constructing fibrous porous materials resistant to impact, shear, and fracture to meet the needs of practical applications; developing multifunctional stealth fibrous porous materials to confer full-spectrum broadband stealth capability; and exploring the relationship between material size and mechanical properties as a basis for preparing large-scale samples that meet the application's requirement. This review is very timely and aims to focus researchers' attention on the importance and research progress of fibrous porous materials in the field of stealth protection, so as to solve the problems and challenges of fibrous porous materials in the field of stealth protection and to promote the further innovation of fibrous porous materials in terms of structure and function.

Soft Robotic Textiles for Adaptive Personal Thermal Management

Thermal protective textiles are crucial for safeguarding individuals, particularly firefighters and steelworkers, against extreme heat, and for preventing burn injuries. However, traditional firefighting gear suffers from statically fixed thermal insulation properties, potentially resulting in overheating and discomfort in moderate conditions, and insufficient protection in extreme fire events. Herein, an innovative soft robotic textile is developed for dynamically adaptive thermal management, providing superior personal protection and thermal comfort across a spectrum of environmental temperatures. This unique textile features a thermoplastic polyurethane (TPU)-sealed actuation system, embedded with a low boiling point fluid for reversible phase transition, resembling an endoskeleton that triggers an expansion within the textile matrix for enhanced air gap and thermal insulation. The thermal resistance improves automatically from 0.23 to 0.48 Km2 W-1 by self-actuating under intense heat, exceeding conventional textiles by maintaining over 10 °C cooler temperatures. Additionally, the knitted substrate incorporated into the soft actuators can substantially mitigate convective heat transfer, as evidenced by the thermal resistance tests and the temperature mapping derived from numerical simulations. Moreover, it boasts significantly increased moisture permeability. The thermoadaptation and breathability of this durable all-fabric system signify considerable progress in the development of protective clothing with high comfort for dynamic and extreme temperature conditions.

Visible Microfluidic Deprotonation for Aramid Nanofibers as Building Blocks of Cascade-Microfluidic-Processed Colloidal Aerogels

 Microfluidic deprotonation approach is proposed to realize continuous, scalable, efficient, and uniform production of aramid nanofibers (ANFs) by virtue of large specific surface area, high mixing efficiency, strong heat transfer capacity, narrow residence time distribution, mild laminar-flow process, and amplification-free effect of the microchannel reactor. By means of monitoring capabilities endowed by the high transparency of the microchannel, the kinetic exfoliation process of original aramid particles is in situ observed and the corresponding exfoliation mechanism is established quantificationally. The deprotonated time can be reduced from the traditional several days to 7 min for the final colloidal dispersion due to the synergistic effect between enhanced local shearing/mixing and the rotational motion of aramid particles in microchannel revealed by numerical simulations. Furthermore, the cascade microfluidic processing approach is used to make various ANF colloidal aerogels including aerogel fibers, aerogel films, and 3D-printed aerogel articles. Comprehensive characterizations show that these cascade-microfluidic-processed colloidal aerogels have identical features as those prepared in batch-style mode, revealing the versatile use value of these ANFs. This work achieves significant progress toward continuous and efficient production of ANFs, bringing about appreciable prospects for the practical application of ANF-based materials and providing inspiration for exfoliating any other nano-building blocks.

Woven Agarose-Cellulose Composite Aerogel Fibers with Outstanding Radial Elasticity for Personal Thermal Management

Aerogel fibers are good thermal insulators, suitable for weaving, and show potential as the next generation of intelligent textiles that can effectively reduce heat consumption for personal thermal management. However, the production of continuous aerogel fibers from biomass with sufficient strength and radial elasticity remains a significant challenge. Herein, continuous gel fibers were produced via wet spinning using agarose (AG) as the matrix, 2,2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized cellulose nanofibers (TOCNs) as the reinforcing agent, and no other chemical additives by utilizing the gelling properties of AG. Supercritical drying and chemical vapor deposition (CVD) were then used to produce hydrophobic AG-TOCN aerogel fibers (HATAFs). During CVD, the HATAF gel skeleton was covered with an isostructural silica coating. Consequently, the HATAFs can recover from radial compression under 60% strain. Moreover, the HATAFs have low densities (≤0.14 g cm-3), high porosities (≥91.8%), high specific surface areas (≥188 m2 g-1), moderate tensile strengths (≤1.75 MPa), excellent hydrophobicity (water contact angles of >130°), and good thermal insulating properties at different temperatures. Thus, HATAFs are expected to become a new generation of materials for efficient personal thermal management.

High-Energy Laser Protection Performance of Fibrous Felt-Reinforced Aerogels with Hierarchical Porous Architectures

Continuous-wave lasers can cause irreversible damage to structured materials in a very short time. Modern high-energy laser protection materials are mainly constructed from ceramic, polymer, and metal constitutions. However, these materials are protected by sacrificing their structural integrity under the irradiation of high-energy lasers. In this contribution, we reported multilayer fibrous felt-reinforced aerogels that can sustain the continuous irradiation of a laser at a power density of 120 MW·m-2 without structural damage. It is found that the exceptional high-energy laser protection performance and the comparable mechanical properties of aerogel nanocomposites are attributed to the unique characteristics of hierarchical porous architectures. In comparison with various preparation methods and other aerogel materials, multilayer fibrous felt-reinforced aerogels exhibit the best performance in high-energy laser protection, arising from the gradual interception and the Raman-Rayleigh scattering cycles of a high-energy laser in the porous aerogels. Furthermore, a near-zero thermal expansion coefficient and extremely low thermal conductivity at high temperature allow the lightweight felt-reinforced aerogels to be applied in extreme conditions. The felt-reinforced aerogels reported herein offer an attractive material that can withstand complex thermomechanical stress and retain excellent insulation properties at extremely high temperature.

Mechanically Strengthened Aerogels through Multiscale, Multicompositional, and Multidimensional Approaches: A Review

In recent decades, aerogels have attracted tremendous attention in academia and industry as a class of lightweight and porous multifunctional nanomaterial. Despite their wide application range, the low mechanical durability hinders their processing and handling, particularly in applications requiring complex physical structures. "Mechanically strengthened aerogels" have emerged as a potential solution to address this drawback. Since the first report on aerogels in 1931, various modified synthesis processes have been introduced in the last few decades to enhance the aerogel mechanical strength, further advancing their multifunctional scope. This review summarizes the state-of-the-art developments of mechanically strengthened aerogels through multicompositional and multidimensional approaches. Furthermore, new trends and future directions for as prevailed commercialization of aerogels as plastic materials are discussed.

Hydrophobic Silk Fibroin-Agarose Composite Aerogel Fibers with Elasticity for Thermal Insulation Applications

Aerogel fibers, characterized by their ultra-low density and ultra-low thermal conductivity, are an ideal candidate for personal thermal management as they hold the potential to effectively reduce the energy consumption of room heating and significantly contribute to energy conservation. However, most aerogel fibers have weak mechanical properties or require complex manufacturing processes. In this study, simple continuous silk fibroin-agarose composite aerogel fibers (SCAFs) were prepared by mixing agarose with silk fibroin through wet spinning and rapid gelation, followed by solvent replacement and supercritical carbon dioxide treatment. Among them, the rapid gelation of the SCAFs was achieved using agarose physical methods with heat-reversible gel properties, simplifying the preparation process. Hydrophobic silk fibroin-agarose composite aerogel fibers (HSCAFs) were prepared using a simple chemical vapor deposition (CVD) method. After CVD, the HSCAFs' gel skeletons were uniformly coated with a silica layer containing methyl groups, endowing them with outstanding radial elasticity. Moreover, the HSCAFs exhibited low density (≤0.153 g/cm3), a large specific surface area (≥254.0 m2/g), high porosity (91.1-94.7%), and excellent hydrophobicity (a water contact angle of 136.8°). More importantly, they showed excellent thermal insulation performance in low-temperature (-60 °C) or high-temperature (140 °C) environments. The designed HSCAFs may provide a new approach for the preparation of high-performance aerogel fibers for personal thermal management.

Wearable Aerogels for Personal Thermal Management and Smart Devices

Extreme climates have become frequent nowadays, causing increased heat stress in human daily life. Personal thermal management (PTM), a technology that controls the human body's microenvironment, has become a promising strategy to address heat stress. While effective in ordinary environments, traditional high-performance fibers, such as ultrafine, porous, highly thermally conductive, and phase change materials, fall short when dealing with harsh conditions or large temperature fluctuations. Aerogels, a third-generation superinsulation material, have garnered extensive attention among researchers for their thermal management applications in building energy conservation, transportation, and aerospace, attributed to their extremely low densities and thermal conductivity. While aerogels have historically faced challenges related to weak mechanical strength and limited secondary processing capacity, recent advancements have witnessed notable progress in the development of wearable aerogels for PTM. This progress underscores their potential applications within extremely harsh environments, serving as self-powered smart devices and sensors. This Review offers a timely overview of wearable aerogels and their PTM applications with a particular focus on their wearability and suitability. Finally, the discussion classifies five types of PTM applications based on aerogel function: thermal insulation, heating, cooling, adaptive regulation (involving thermal insulation, heating, and cooling), and utilization of aerogels as wearable smart devices.

Robust and Flame-Retardant Zylon Aerogel Fibers for Wearable Thermal Insulation and Sensing in Harsh Environment

The exceptional lightweight, highly porous, and insulating properties of aerogel fibers make them ideal for thermal insulation. However, current aerogel fibers face limitations due to their low resistance to harsh environments and a lack of intelligent responses. Herein, a universal strategy for creating polymer aerogel fibers using crosslinked nanofiber building blocks is proposed. This approach combines controlled proton absorption gelation spinning with a heat-induced crosslinking process. As a proof-of-concept, Zylon aerogel fibers that exhibited robust thermal stability (up to 650 °C), high flame retardancy (limiting oxygen index of 54.2%), and extreme chemical resistance are designed and synthesized. These fibers possess high porosity (98.6%), high breaking strength (8.6 MPa), and low thermal conductivity (0.036 W m-1 K-1 ). These aerogel fibers can be knotted or woven into textiles, utilized in harsh environments (-196-400 °C), and demonstrate sensitive self-powered sensing capabilities. This method of developing aerogel fibers expands the applications of high-performance polymer fibers and holds great potential for future applications in wearable smart protective fabrics.

Hydrogels and Wound Healing: Current and Future Prospects

The care and rehabilitation of acute and chronic wounds have a significant social and economic impact on patients and global health. This burden is primarily due to the adverse effects of infections, prolonged recovery, and the associated treatment costs. Chronic wounds can be treated with a variety of approaches, which include surgery, negative pressure wound therapy, wound dressings, and hyperbaric oxygen therapy. However, each of these strategies has an array of limitations. The existing dry wound dressings lack functionality in promoting wound healing and exacerbating pain by adhering to the wound. Hydrogels, which are commonly polymer-based and swell in water, have been proposed as potential remedies due to their ability to provide a moist environment that facilitates wound healing. Their unique composition enables them to absorb wound exudates, exhibit shape adaptability, and be modified to incorporate active compounds such as growth factors and antibacterial compounds. This review provides an updated discussion of the leading natural and synthetic hydrogels utilized in wound healing, details the latest advancements in hydrogel technology, and explores alternate approaches in this field. Search engines Scopus, PubMed, Science Direct, and Web of Science were utilized to review the advances in hydrogel applications over the last fifteen years.

Mimicking polar bear hairs in aerogel fibers

Encapsulated aerogel fibers offer thermal insulation, breathability, and strength.

Biomimetic, knittable aerogel fiber for thermal insulation textile

Aerogels have been considered as an ideal material for thermal insulation. Unfortunately, their application in textiles is greatly limited by their fragility and poor processability. We overcame these issues by encapsulating the aerogel fiber with a stretchable layer, mimicking the core-shell structure of polar bear hair. Despite its high internal porosity over 90%, our fiber is stretchable up to 1000% strain, which is greatly improved compared with that of traditional aerogel fibers (~2% strain). In addition to its washability and dyeability, our fiber is mechanically robust, retaining its stable thermal insulation property after 10,000 stretching cycles (100% strain). A sweater knitted with our fiber was only one-fifth as thick as down, with similar performance. Our strategy for this fiber provides rich possibilities for developing multifunctional aerogel fibers and textiles.

Direct Synthesis of Polyimide Curly Nanofibrous Aerogels for High-Performance Thermal Insulation Under Extreme Temperature

Maintaining human body temperature is one of the basic needs for living, which requires high-performance thermal insulation materials to prevent heat exchange with external environment. However, the most widely used fibrous thermal insulation materials always suffer from the heavy weight, weak mechanical property, and moderate capacity to suppress heat transfer, resulting in limited personal cold and thermal protection performance. Here, an ultralight, mechanically robust, and thermally insulating polyimide (PI) aerogel is directly synthesized via constructing 3D interlocked curly nanofibrous networks during electrospinning. Controlling the solution/water molecule interaction enables the rapid phase inversion of charged jets, while the multiple jets are ejected by regulating charge density of the fluids, thus synergistically allowing numerous curly nanofibers to interlock and cross-link with each other to form porous aerogel structure. The resulted PI aerogel integrates the ultralight property with density of 2.4 mg cm-3 , extreme temperature tolerance (mechanical robustness over -196 to 300 °C), and thermal insulation performance with ultralow thermal conductivity of 22.4 mW m-1 K-1 , providing an ideal candidate to keep human thermal comfort under extreme temperature. This work can provide a source of inspiration for the design and development of nanofibrous aerogels for various applications.

Folk arts-inspired twice-coagulated configuration-editable tough aerogels enabled by transformable gel precursors

Aerogels, as famous lightweight and porous nanomaterials, have attracted considerable attention in various emerging fields in recent decades, however, both low density and weak mechanical performance make their configuration-editing capability challenging. Inspired by folk arts, herein we establish a highly efficient twice-coagulated (TC) strategy to fabricate configuration-editable tough aerogels enabled by transformable gel precursors. As a proof of concept, aramid nanofibers (ANFs) and polyvinyl alcohol (PVA) are selected as the main components of aerogel, among which PVA forms a flexible configuration-editing gel network in the first coagulation process, and ANF forms a configuration-locking gel network in the second coagulation process. TC strategy guarantees the resulting aerogels with both high toughness and feasible configuration editing capability individually or simultaneously. Altogether, the resulting tough aerogels with special configuration through soft to hard modulation provide great opportunities to break through the performance limits of the aerogels and expand application areas of aerogels.

Fast and scalable production of crosslinked polyimide aerogel fibers for ultrathin thermoregulating clothes

Polyimide aerogel fibers hold promise for intelligent thermal management fabrics, but their scalable production faces challenges due to the sluggish gelation kinetics and the weak backbone strength. Herein, a strategy is developed for fast and scalable fabrication of crosslinked polyimide (CPI) aerogel fibers by wet-spinning and ambient pressure drying via UV-enhanced dynamic gelation strategy. This strategy enables fast sol-gel transition of photosensitive polyimide, resulting in a strongly-crosslinked gel skeleton that effectively maintains the fiber shape and porous nanostructure. Continuous production of CPI aerogel fibers (length of hundreds of meters) with high specific modulus (390.9 kN m kg-1) can be achieved within 7 h, more efficiently than previous methods (>48 h). Moreover, the CPI aerogel fabric demonstrates almost the same thermal insulating performance as down, but is about 1/8 the thickness of down. The strategy opens a promisingly wide-space for fast and scalable fabrication of ultrathin fabrics for personal thermal management.

Bioinspired Thermochromic Textile Based on Robust Cellulose Aerogel Fiber for Self-Adaptive Thermal Management and Dynamic Labels

Aerogel fiber has emerged recently for incorporation in personal thermal management textiles due to its flexibility, scalability, and ultrahigh porosity, which allows the body to keep warm via thermal isolation without energy consumption. However, the functionalization and intellectualization of cellulose-based aerogel fibers have not yet been fully developed. Herein, we propose a biomimicking design inspired by polar bear and Siamese cat hair that combines porous cellulose aerogel fiber (CAF) with reversible thermochromic microcapsules to mimic biological sensory and adaptive thermoregulation functions. The produced CAF has a controllable pore structure, a large specific surface area (230 m2/g), and excellent mechanical strength (∼15 MPa). Low-temperature darkening microcapsules have been incorporated into the robust CAF to spontaneously adjust color by perceiving the ambient temperature. The functional aerogel fiber fabric achieves high thermal insulation and photothermal modulation simultaneously at temperatures below 18 °C. The temperature of the thermochromic fabric was higher by 6 °C than that of the sample without the microcapsules at a light intensity of 0.2 W/cm2. In addition, the aerogel fibers mixed with two types of thermochromic microcapsules exhibit three color switches with fast response, a color-control precision of 0.2 °C, and good cycling performance. This smart aerogel fibers hold great promise for self-adaptive thermal management, temperature indication, information transfer, and anticounterfeiting in textiles.