Self-charging electrostatic face masks leveraging triboelectrification for prolonged air filtration

Sustainable self-powered PVDF fibrous filter medias based on triboelectric nanogenerator with efficient dust collection for personal occupational protection

The filtration efficiency of traditional filter medias is relatively low for the removal of fine dusts ranging from 10 to 1000 nm, which is seriously harmful to human health. In this study, a novel self-powered fibrous filter media based on polyvinylidene fluoride/cellulose acetate (PVDF/CA) electrospun nanofibrous membrane and a triboelectric nanogenerator (TENG) driven by respiration (R-TENG) was developed. Two different electrets including hydroxylation graphene (G-OH) and cesium lead halide inorganic chalcocite (CsPbI2Br) were added to improve the filtration performance of PVDF/CA membranes. The results showed that the filtration efficiency of the PVDF/CA/G-OH membrane for NaCl particles arrived at 96.8 %, with a pressure drop of 132.5 Pa, a tensile strength of 2.88 MPa and permeability of 221.45 mm/s. Compared with the R-TENG fabricated by the PVDF/CA membrane, the short-circuit current, the open-circuit voltage and the transferred charge of the R-TENG fabricated by the PVDF/CA/G-OH membrane (2.91 μA, 12.84 V and 14.23 nC) largely increased, representing a increase of 2.03, 1.74 and 1.99 times respectively. On the basis of the R-TENG, the self-powered fibrous filter medias showed a higher filtration efficiency and lower pressure drop for the fine particulates after continuous use for 240 min at the huge flow rates of 85 L/min. Combined with the COMSOL simulation, it could be found that R-TENG continuously provided electrostatic charge on the fibrous membranes and promoted the ionization of gas molecules to effectively capture the fine dusts, exhibiting an excellent air purification method with great prospects in wearable breathing devices for occupational health protection.

Fully-biodegradable and self-powered intelligent filter assembled by fibrous cellulose and MOF-functionalized poly(lactic acid) core-shell nanofibers for active PM capturing and passive respiratory sensing

With the increasing demand for ecofriendly air filtration materials, poly(lactic acid) (PLA) nanofibrous membranes (NFMs) show significant potential for efficient air purification while evading plastic pollution. However, there is still an urgent need to solve the issues of intrinsically low electroactivity and poor electret performance for PLA. Here, we prepared MOF-functionalized core-shell beaded PLA (MCSB-PLA) gradient nanofibers at fibrous cellulose, featuring a PLA/MOF-5 composite shell layer by coaxial electrospinning. Under the action of high-voltage electric field, MOF-5 nanocrystals were ready to interact with PLA chains, prompting the generation of highly refined and electroactive nanofibers. The MCSB-PLA NFMs were characterized by ultrafine fibers (diameter decrease of 23.5 %) and MOF-triggered bead-on-string microstructures. Meanwhile, both the surface potential and dielectric constant were largely elevated for MCSB-PLA NFMs (up to 5.2 kV and 1.86, respectively), accompanied by excellent tribo-output performance (236.8 % and 161.9 % increase in output voltage and current, respectively). Given the increased electroactivity, MCSB-PLA NFMs showed high-efficiency PM0.3 filtration (93.4 %, 106 Pa, at 32 L/min), representing an increase of 12.26 % compared to pure PLA counterpart (only 83.2 %). Even under high-humidity conditions, 91.3 % removal of PM0.3 was realized by MCSB-PLA (at 90 %RH and 32 L/min). Furthermore, the self-powered mechanisms were integrated with MCSB-PLA/cellulose, permitting real-time monitoring of physiological signals. The proposed degradable and highly electroactive MCSB-PLA NFMs is highly promising for air purification and passive healthcare.

Self-Cleaning Microwave-Responsive MXene-Coated Filtration System for Enhanced Airborne Virus Disinfection

The COVID-19 pandemic has highlighted the urgent demand for advanced air disinfection technologies. Traditional air filters primarily capture large airborne particles but are ineffective against submicrometer aerosols. This study introduces a microwave-enabled catalytic air filtration system using Ti3C2Tx MXene-coated polypropylene filters to enhance air disinfection. With only 0.05 mg·cm-2 of MXene coating, the filter surface temperature rapidly reached 104 °C within 3 s under 125 W microwave irradiation. Such surface heating led to a significantly higher log removal value (LRV) (1.86 ± 0.47) of the MS2 bacteriophage in the synthetic bioaerosol with an initial concentration of 105 PFU·mL-1, compared to 0.24-0.38 achieved by the pristine filter or the MXene-coated filter without microwave irradiation. Additionally, the filter surface exhibited promising self-cleaning behavior, as indicated by the stable viral inactivation and removal efficiency even in high-humidity environments. This innovative air filtration technology shows promising potential for preventing airborne pathogen transmission and protecting public health across diverse environmental conditions.

Bicomponent Electrospinning of PVDF-Based Nanofiber Membranes for Air Filtration and Oil-Water Separation

Particulate matter (PM) and water pollution have posed serious hazards to human health. Nanofiber membranes (NFMs) have emerged as promising candidates for the elimination of PMs and the separation of oil-water mixtures. In this study, a polyvinylidene difluoride (PVDF)-based nanofiber membrane with an average diameter of approximately 150 nm was prepared via a double-nozzle electrospinning technology, demonstrating high-efficiency PM filtration and oil-water separation. The finer fiber diameter not only enhances PM filtration efficiency but also reduces air resistance. The high-voltage electric field and mechanical stretching during electrospinning promote high crystallization of β-phase PVDF. Additionally, the electrostatic charges generated on the surface of β-phase PVDF facilitate the adsorption of PM from the atmosphere. The introduction of polydopamine (PDA) in PVDF produces abundant adsorption sites, enabling outstanding filtration performance. PVDF-PVDF/PDA NFMs can achieve remarkable PM0.3 filtration efficiency (99.967%) while maintaining a low pressure drop (144 Pa). PVDF-PVDF/PDA NFMs are hydrophobic, and its water contact angle (WCA) is 125.9°. It also shows excellent resistance to both acidic and alkaline environments, along with notable flame retardancy, as it can self-extinguish within 3 s. This nanofiber membrane holds significant promise for applications in personal protection, indoor air filtration, oily wastewater treatment, and environmental protection.

Self-powered Wraparound (Abaxial) Droplet Deposition via a Superhydrophobic Surface Aid

Many diseases and pests are fond of the backs of leaves, making wraparound deposition essential for enhancing agrochemical utilization and minimizing environmental hazards. We present a superhydrophobic surface decorated with fluorinated-SiO2 nanoparticles on the adaxial (front) side, improving sprayed droplet wraparound behaviors and achieving a 10-fold increase in abaxial (backside) deposition without using an electrostatic sprayer. Solid-liquid contact electrification boosts the positive charge-to-mass ratio of rebound spraying from 17 to 454 nC g-1, with the abaxial surface acquiring opposite electric charges at kilovolt-level voltages. This intensified droplet-solid electrostatic attraction guides droplets to wrap around and deposit on the abaxial surface. Further, a homemade fluorinated superhydrophobic tube enhances spray charge and abaxial deposition density on superhydrophobic plant leaves by 47- and 5- times, respectively, compared to those obtained via direct spraying. This work will significantly improve agrochemical efficiency, reducing environmental risks in sustainable agriculture and related industries.

High-efficiency respiratory protection and intelligent monitoring by nanopatterning of electroactive poly(lactic acid) nanofibers

The advent of multifunctional nanofibrous membranes (NFMs) has led to the development of next-generation air filters that are ready to intercept fine particulate matters (PMs) and monitor the respiratory diseases. However, it is still challenging to fabricate biodegradable NFMs featuring the desirable combination of high filtration efficiencies, low air resistance, and intelligent real-time monitoring. Herein, a hierarchical nanopatterning approach was proposed to functionalize the stereocomplexed poly(lactic acid) (PLA) (SC-PLA) nanofibers via the combined electrospinning of SC-PLA and electrospray of CNT@ZIF-8 nanohybrids. The nanopatterned SC-PLA (NSC-PLA) NFMs were characterized by largely increased surface activity and electroactivity, as evidenced by the nearly two-fold increase in surface potential (up to 7.3 kV) and substantial improvements in the dielectric properties. Furthermore, the NSC-PLA NFMs exhibited excellent tribo-output performance, yielding a voltage of as high as 13.5 V for NSC-PLA NFMs loaded 10 % nanohybrids (NSC-PLA10). In particular, the exceptionally high electroactivity and unique protrusion structure together contributed to promote the filtration efficiencies, while providing a low pressure drop (e.g., 96.1 % for PM2.5 and 88.3 % for PM0.3, only 67.6 Pa of NSC-PLA10, at 32 L/min). More importantly, NSC-PLA NFMs enabled real-time monitoring of physiological signals during different respiratory states, as evidenced by the output voltages of 17.2, 32.9 and 37.5 mV for normal breath, fast breath and cough recorded by NSC-PLA10. The proposed NSC-PLA NFMs show enormous potential in the fields of air filtration and real-time respiratory monitoring, thus providing ecofriendly solutions to personal health management.

Electrospun multifunctional nanofibers for advanced wearable sensors

The multifunctional extension of fiber-based wearable sensors determines their integration and sustainable development, with electrospinning technology providing reliable, efficient, and scalable support for fabricating these sensors. Despite numerous studies on electrospun fiber-based wearable sensors, further attention is needed to leverage composite structural engineering for functionalizing electrospun fibers. This paper systematically reviews the research progress on fiber-based multifunctional wearable sensors in terms of design concept, device fabrication, mechanism exploration, and application potential. Firstly, the basics of electrospinning are briefly introduced, including its development, principles, parameters, and material selection. Tactile sensors, as crucial components of wearable sensors, are discussed in detail, encompassing their performance parameters, transduction mechanisms, and preparation strategies for pressure, strain, temperature, humidity, and bioelectrical signal sensors. The main focus of the article is on the latest research progress in multifunctional sensing design concepts, multimodal decoupling mechanisms, sensing mechanisms, and functional extensions. These extensions include multimodal sensing, self-healing, energy harvesting, personal thermal management, EMI shielding, antimicrobial properties, and other capabilities. Furthermore, the review assesses existing challenges and outlines future developments for multifunctional wearable sensors, highlighting the need for continued research and innovation.

Exhaled Breath Analysis: From Laboratory Test to Wearable Sensing

Breath analysis and monitoring have emerged as pivotal components in both clinical research and daily health management, particularly in addressing the global health challenges posed by respiratory and metabolic disorders. The advancement of breath analysis strategies necessitates a multidisciplinary approach, seamlessly integrating expertise from medicine, biology, engineering, and materials science. Recent innovations in laboratory methodologies and wearable sensing technologies have ushered in an era of precise, real-time, and in situ breath analysis and monitoring. This comprehensive review elucidates the physical and chemical aspects of breath analysis, encompassing respiratory parameters and both volatile and non-volatile constituents. It emphasizes their physiological and clinical significance, while also exploring cutting-edge laboratory testing techniques and state-of-the-art wearable devices. Furthermore, the review delves into the application of sophisticated data processing technologies in the burgeoning field of breathomics and examines the potential of breath control in human-machine interaction paradigms. Additionally, it provides insights into the challenges of translating innovative laboratory and wearable concepts into mainstream clinical and daily practice. Continued innovation and interdisciplinary collaboration will drive progress in breath analysis, potentially revolutionizing personalized medicine through entirely non-invasive breath methodology.

Hybrid Nanofibrous Membrane with Durable Electret for Anti-Wetting Air Filtration

Electrospun fibrous materials with fine fibers and small pores are fundamental for particulate matter (PM) filtration, addressing its harmful environmental and health impacts. However, the existing electrospun fibers are still limited to their sub-micron diameters and unstable surface electrostatic effect, leading to deteriorated filtration performance after prolonged storage or wetting. Herein, the study creates nanofibrous membranes with long-time stable electrostatics by electret-enhanced electrospinning. The phase separation and polarization of the charged jet are manipulated to achieve rapid stretch and strong electret. The obtained membrane exhibits nanosized structures with fiber diameters of ≈220 nm, pore size <1 µm, as well as robust surface potential of 0.4 kV. By virtue of the synergistic effects of sieving and adsorption, the nanofibrous membrane showed a remarkable PM0.3 filtration efficiency of 96.6% and pressure drop of 140 Pa, even reaching the N90 standard after five wetting cycles. The design of such durable membranes will offer a new sight in the functional filtration materials.

Next-generation air filtration nanotechnology for improved indoor air quality

Indoor air quality (IAQ) significantly affects human health, with pollutants such as organic, inorganic substances, and biological contaminants contributing to various respiratory, neurological, and immunological diseases. In this review, we highlighted the need for advanced air filtration technologies to mitigate these pollutants, which are emitted from household products, building materials, combustion processes, and bioaerosols. While traditional HVAC systems and mechanical filtration methods have been effective, they are often energy-intensive and limited in their ability to capture specific pollutants. To address these limitations, nanotechnology-based air filtration technologies, particularly those utilizing electrospinning processes, offer promising alternatives. This review classifies pollutants and details the working principles of next-generation filters, focusing on passive, self-powered, and externally powered mechanisms. These advanced filters achieve high filtration efficiency with minimal pressure drop, enhanced pollutant capture, and in some cases, health monitoring capabilities. This review emphasizes the significance of ongoing research into eco-friendly and sustainable filtration systems to enhance IAQ and minimize health risks linked to long-term exposure to indoor air pollutants.

Highly air-permeable and dust-holding protective membranes by hierarchical structuring of electroactive poly(lactic acid) micro- and nanofibers

The application of biodegradable electrospun poly(lactic acid) (PLA) fibrous membranes (FMs) toward respiratory protection has long been dwarfed by the poor electret effect and short service life. Herein, a micro-on-nano (MON) approach was proposed to fabricate highly electroactive dual-scale poly(lactic acid) (DS-PLA) FMs consisting of inner-layer nanofibers (667 nm) and outer-layer microfibers (1.22 µm). Customized Ag-decorated BTO (Ag-BTO) dielectrics were incorporated to improve the electret effect and charge storage stability of DS-PLA FMs, contributing to the improved dielectric constants (1.40), surface potential (11.4 kV), and triboelectric performance (output voltage of 34.2 V at 10 N, 0.5 Hz). The unique hierarchies and profound electrostatic adsorption effect synergistically allowed the DS-PLA FMs to achieve high PM filtration efficiencies (99.10 % for PM2.5, 90.37 % for PM0.3, 32 L/min) at a reduced pressure drop (only 58.8 Pa). Furthermore, benefiting from the cascade filtration mechanisms, the DS-PLA FMs demonstrated superior dust holding capacity (9.4 g/m2), which was 3.2 times higher than that of normal PLA. With the assistance of convolutional neural network (CNN), a set of breathing patterns could be recognized with a classification accuracy as high as 96.7 %. This work provides a facile pathway to significantly prolong the service life of electrospun PLA filters for high-performance air filtration and deep learning-assisted respiratory monitoring.

Advanced Dielectric Materials for Triboelectric Nanogenerators: Principles, Methods, and Applications

Triboelectric nanogenerator (TENG) manifests distinct advantages such as multiple structural selectivity, diverse selection of materials, environmental adaptability, low cost, and remarkable conversion efficiency, which becomes a promising technology for micro-nano energy harvesting and self-powered sensing. Tribo-dielectric materials are the fundamental and core components for high-performance TENGs. In particular, the charge generation, dissipation, storage, migration of the dielectrics, and dynamic equilibrium behaviors determine the overall performance. Herein, a comprehensive summary is presented to elucidate the dielectric charge transport mechanism and tribo-dielectric material modification principle toward high-performance TENGs. The contact electrification and charge transport mechanism of dielectric materials is started first, followed by introducing the basic principle and dielectric materials of TENGs. Subsequently, modification mechanisms and strategies for high-performance tribo-dielectric materials are highlighted regarding physical/chemical, surface/bulk, dielectric coupling, and structure optimization. Furthermore, representative applications of dielectric materials based TENGs as power sources, self-powered sensors are demonstrated. The existing challenges and promising potential opportunities for advanced tribo-dielectric materials are outlined, guiding the design, fabrication, and applications of tribo-dielectric materials.

High-Temperature-Resistant Dual-Scale Ceramic Nanofiber Films toward Improved Air Filtration

Currently, air pollution primarily arises from industrial emissions, coal combustion, and automobile exhaust, posing significant challenges for mitigation. This highlights the urgent need for advanced and efficient filtration materials with low pressure drop and high-temperature resistance. Traditionally, improving filtration property has involved increasing the thickness of the filtration materials, which consequently leads to higher costs. Here, dual-scale mullite nanofiber (MNF) films containing interwoven thick nanofibers (606 nm) and thin nanofibers (186 nm) are prepared using solution blow spinning. The dual-scale structure design enables the films to maintain a low pressure drop while achieving high filtration efficiency. At an airflow velocity of 5.3 cm s-1, the films with an areal density of 3.8 mg cm-2, achieve a filtration efficiency of 98.23% and a pressure drop of 141 Pa for PM0.3. In addition, the MNF films exhibit excellent flexibility and high-temperature resistance, making them have great potential for use in high-temperature flue gas filtration.

Biodegradable Poly (L-Lactic acid) Fibrous Membrane with Ribbon-Structured Fibers and Ultrafine Nanofibers Enhances Air Filtration Performance

Here, the poly (l-lactic acid) (PLLA) membrane with multi-structured networks (MSN) is successfully prepared by electrospinning technology for the first time. It is composed of micron-sized ribbon-structured fibers and ultrafine nanofibers with a diameter of tens of nanometers, and they are connected to form the new network structure. Thanks to the special fiber morphology and structure, the interception and electrostatic adsorption ability for against atmospheric particulate matter (PM) are significantly enhanced, and the resistance to airflow is reduced due to the "slip effect" caused by ultrafine nanofibers. The PLLA MSN membrane shows excellent filtration performance with ultra-high filtration efficiency (>99.9% for PM2.5 and >99.5% for PM0.3) and ultra-low pressure drop (≈20 Pa). It has demonstrated filtration performance that even exceeds current non-biodegradable polymer materials, laying the foundation for future applications of biodegradable PLLA in the field of air filtration. In addition, this new structure also provides a new idea for optimizing the performance of other polymer materials.

Application of Biomass-Based Triboelectrification for Particulate Matter Removal

Electrostatic fields are crucial for achieving the highly efficient filtration of airborne pollutants. However, the dissipation of static charges over time, especially under humid conditions, limits their practical application. In this study, we present a self-charging air filter (SAF) powered by a triboelectric nanogenerator (TENG). This SAF is integrated into a commercial mask, termed SAFM, which can effectively capture and degrade airborne pollutants without requiring an external power source. By leveraging the triboelectric effect during breathing, the TENG within the SAFM continuously replenishes static charges, maintaining the triboelectric field. The system employs a cellulose aerogel/Ti3C2Tx composite as the electron donor and an esterified cellulose-based electrospun nanofiber as the electron acceptor. Remarkably, the triboelectric field significantly enhances filtration performance, with the SAF achieving up to 95.7% filtration efficiency for particulate matter as small as 0.3 μm. This work underscores the potential of TENG-powered triboelectric fields in the development of multifunctional, human-machine interactive facemasks.

Hierarchically Nano-Decorated Poly(lactic acid) Nanofibers for Humidity-Resistant Respiratory Healthcare and High-Accuracy Disease Diagnosis

The application of biodegradable and eco-friendly poly(lactic acid) (PLA) nanofibrous membranes (NFMs) toward respiratory healthcare has long been thwarted by the poor electroactivity and low surface activity of PLA. Herein, we unravel a microwave-assisted route to fabricate rod-like ZnO nanodielectrics, which were decorated with dopamine (ZnO@PDA) and anchored at the PLA nanofibers via an electrospinning-electrospray approach. The PLA/ZnO@PDA NFMs featured a substantially elevated specific surface area (up to 20.7 m2/g), increased dielectric constant (nearly 1.8) and a surface potential as high as 9.5 kV, resulting in superior air filtering performance (99.45% for PM0.3, 94.1 Pa, 32 L/min) compared with the pure PLA counterpart (90.04%, 169.0 Pa, 32 L/min). The notably increased electroactivity endowed the PLA/ZnO@PDA NFMs with significant improvements in triboelectric properties (output voltage of 11.5 V at 10 N, 0.5 Hz), laying down the cornerstone for self-powered monitoring of personal respiration. More importantly, a deep learning-assisted diagnostic system was developed based on respiration-driven signal patterns, enabling intelligent and real-time disease diagnosis with 100% accuracy for the protective membranes. The proposed hierarchical nanodecoration strategy opens up new possibilities for engendering eco-friendly nanofibers with an exceptional combination of efficient respiratory healthcare and intelligent diagnosis.

Interfacial Polarization Strategy to Electroactive Poly(lactic acid) Nanofibers for Humidity-Resistant Respiratory Protection and Machine Learning-Assisted Monitoring

The advancement of intelligent and biodegradable respiratory protection equipment is pivotal in the realm of human health engineering. Despite significant progress, achieving a balance between efficient filtration and intelligent monitoring remains a great challenge, especially under conditions of high relative humidity (RH) and high airflow rate (AR). Herein, we proposed an interfacial stereocomplexation (ISC) strategy to facilitate intensive interfacial polarization for poly(lactic acid) (PLA) nanofibrous membranes, which were customized for machine learning-assisted respiratory diagnosis. Theoretical principles underlying the facilitated formation of the electroactive phase and aligned PLA chains were quantitatively depicted in the ISC-PLA nanofibers, contributing to the increased dielectric constant and surface potential (as high as 2.2 and 5.1 kV, respectively). Benefiting from the respiration-driven triboelectric mechanisms, the ISC-PLA demonstrated a high PM0.3 filtration efficiency of over 99% with an ultralow pressure drop (75 Pa), even in challenging circumstances (95 ± 5% RH, AR of 85 L/min). Furthermore, we implemented the ISC-PLA with multifunction respiratory monitoring (response time of 0.56 s and recovery time of 0.25 s) and wireless transmission technology, yielding a high recognition rate of 83% for personal breath states. This innovation has practical implications for health management and theoretical advancements in respiratory protection equipment.

Advances in Machine Learning for Wearable Sensors

Recent years have witnessed tremendous advances in machine learning techniques for wearable sensors and bioelectronics, which play an essential role in real-time sensing data analysis to provide clinical-grade information for personalized healthcare. To this end, supervised learning and unsupervised learning algorithms have emerged as powerful tools, allowing for the detection of complex patterns and relationships in large, high-dimensional data sets. In this Review, we aim to delineate the latest advancements in machine learning for wearable sensors, focusing on key developments in algorithmic techniques, applications, and the challenges intrinsic to this evolving landscape. Additionally, we highlight the potential of machine-learning approaches to enhance the accuracy, reliability, and interpretability of wearable sensor data and discuss the opportunities and limitations of this emerging field. Ultimately, our work aims to provide a roadmap for future research endeavors in this exciting and rapidly evolving area.

Emerging Trends of Nanofibrous Piezoelectric and Triboelectric Applications: Mechanisms, Electroactive Materials, and Designed Architectures

Over the past few decades, significant progress in piezo-/triboelectric nanogenerators (PTEGs) has led to the development of cutting-edge wearable technologies. Nanofibers with good designability, controllable morphologies, large specific areas, and unique physicochemical properties provide a promising platform for PTEGs for various advanced applications. However, the further development of nanofiber-based PTEGs is limited by technical difficulties, ranging from materials design to device integration. Herein, the current developments in PTEGs based on electrospun nanofibers are systematically reviewed. This review begins with the mechanisms of PTEGs and the advantages of nanofibers and nanodevices, including high breathability, waterproofness, scalability, and thermal-moisture comfort. In terms of materials and structural design, novel electroactive nanofibers and structure assemblies based on 1D micro/nanostructures, 2D bionic structures, and 3D multilayered structures are discussed. Subsequently, nanofibrous PTEGs in applications such as energy harvesters, personalized medicine, personal protective equipment, and human-machine interactions are summarized. Nanofiber-based PTEGs still face many challenges such as energy efficiency, material durability, device stability, and device integration. Finally, the research gap between research and practical applications of PTEGs is discussed, and emerging trends are proposed, providing some ideas for the development of intelligent wearables.

Hyperbranched Polymer Induced Antibacterial Tree-Like Nanofibrous Membrane for High Effective Air Filtration

The air filtration materials with high efficiency, low resistance, and extra antibacterial property are crucial for personal health protection. Herein, a tree-like polyvinylidene fluoride (PVDF) nanofibrous membrane with hierarchical structure (trunk fiber of 447 nm, branched fiber of 24.7 nm) and high filtration capacity is demonstrated. Specifically, 2-hydroxypropyl trimethyl ammonium chloride terminated hyperbranched polymer (HBP-HTC) with near-spherical three-dimensional molecular structure and adjustable terminal positive groups is synthesized as an additive for PVDF electrospinning to enhance the jet splitting and promote the formation of branched ultrafine nanofibers, achieving a coverage rate of branched nanofibers over 90% that is superior than small molecular quaternary ammonium salts. The branched nanofibers network enhances mechanical properties and filtration efficiency (99.995% for 0.26 µm sodium chloride particles) of the PVDF/HBP-HTC membrane, which demonstrates reduced pressure drop (122.4 Pa) and a quality factor up to 0.083 Pa-1 on a 40 µm-thick sample. More importantly, the numerous quaternary ammonium salt groups of HBP-HTC deliver excellent antibacterial properties to the PVDF membranes. Bacterial inhibitive rate of 99.9% against both S. aureus and E. coli is demonstrated in a membrane with 3.0 wt% HBP-HTC. This work provides a new strategy for development of high-efficiency and antibacterial protection products.

Tribo-charge enhanced and cellulose based biodegradable nanofibrous membranes with highly fluffy structure for air filtration and self-powered respiration monitoring systems

Recently, the demand for healthcare products especially wearable smart masks is increasing. The biosafety and degradability of smart masks are crucial for human health and environmental protection. However, the development of biodegradable and biocompatible fibrous membranes with high filtration efficiency and low pressure drop is still a challenge. How to realize the collaborative improvement between air filtration efficiency and pressure drop of the nanofibrous membrane is still a challenge. Here, a tribo-charge enhanced and biodegradable nanofibrous membranes (TCB NFMs) with highly fluffy structure for air filtration and self-powered respiration monitoring systems is reported for the first time. The filtration efficiency and pressure drop of the prepared membranes for 0.3 µm NaCl particulates is 99.971% and 41.67 Pa. The TCB NFMs based smart mask possesses a series of satisfactory and excellent characteristics, such as self-powered, biodegradable, biocompatible, high filtration efficiency, and low pressure drop, which is highly promising for application in air filtration systems and intelligent wearable respiration monitoring systems.

Nanopatterning of beaded poly(lactic acid) nanofibers for highly electroactive, breathable, UV-shielding and antibacterial protective membranes

Despite great potential in fabrication of biodegradable protective membranes by electrospinning of poly(lactic acid) (PLA) nanofibers, it is still thwarted by smooth surfaces and poor electroactivity that challenge the promotion of electret properties and long-term air filtration performance. Here, a microwave-assisted synthetic method was used to customize dielectric TiO2 nanocrystals of ultrasmall and uniform dimensions (∼30 nm), which were homogeneously embedded at beaded PLA nanofibers (PLA@TiO2, diameter of around 280 nm) by the combined "electrospinning-electrospray" approach. With small amounts of TiO2 (2, 4 and 6 wt%), the nanopatterned PLA@TiO2 nanofibrous membranes (NFMs) were characterized by largely increased dielectric constants (nearly 1.9), surface potential (up to 1.63 kV) and triboelectric properties (output voltage of 12.2 V). Arising from the improved electroactivity and self-charging mechanisms, the nanopatterned PLA@TiO2 NFMs exhibited remarkable PM0.3 filtration properties (97.9 %, 254.6 Pa) even at the highest airflow rate of 85 L/min, surpassing those of pure PLA membranes (86.2 %, 483.7 Pa). This was moreover accompanied by inhibition rates of 100 % against both E. coli and S. aureus, as well as excellent UV-blocking properties (UPF as high as 3.8, TUVA of 50.9 % and TUVB of 20.1 %). The breathable and electroactive nanopatterned PLA NFMs permit promising applications in multifunctional protective membranes toward excellent UV shielding and high-efficiency removal of both PMs and pathogens.

Ultrathin, ultralight dual-scale fibrous networks with high-infrared transmittance for high-performance, comfortable and sustainable PM0.3 filter

Highly permeable particulate matter (PM) can carry various bacteria, viruses and toxics and pose a serious threat to public health. Nevertheless, current respirators typically sacrifice their thickness and base weight for high-performance filtration, which inevitably causes wearing discomfort and significant consumption of raw materials. Here, we show a facile yet massive splitting eletrospinning strategy to prepare an ultrathin, ultralight and radiative cooling dual-scale fiber membrane with about 80% infrared transmittance for high-protective, comfortable and sustainable air filter. By tailoring antibacterial surfactant-triggered splitting of charged jets, the dual-scale fibrous filter consisting of continuous nanofibers (44 ± 12 nm) and submicron-fibers (159 ± 32 nm) is formed. It presents ultralow thickness (1.49 μm) and base weight (0.57 g m-2) but superior protective performances (about 99.95% PM0.3 removal, durable antibacterial ability) and wearing comfort of low air resistance, high heat dissipation and moisture permeability. Moreover, the ultralight filter can save over 97% polymers than commercial N95 respirator, enabling itself to be sustainable and economical. This work paves the way for designing advanced and sustainable protective materials.

Evaluating Droplet Survivability on Face Masks with X-ray Microtomography

When a person talks, coughs, or sneezes, respiratory droplets are expelled and inevitably land on several surfaces, representing a route for respiratory disease transmission. Here, face masks act as a barrier by obstructing the passage of droplets during exhalation and inhalation. Being constantly exposed to respiratory events and carrying droplet residue, understanding the evaporation and absorption dynamics for tiny droplets on face masks and the fate of viral particle deposition is necessary to analyze the contamination risk. We explore the ideal design for masks from the interaction of mask surfaces with surrogate respiratory droplets by X-ray microscopy and microtomography. We show that the respiratory droplet survivability is significantly reduced in masks with a hydrophilic surface where absorption takes place, leading to a reduction of the postevaporation droplet residue at the mask surface compared with a hydrophobic surface. The results allow us to propose a better mask layer design dependent on wettability, reducing the risk of contamination from respiratory droplets.

One-Step Fast Fabrication of Electrospun Fiber Membranes for Efficient Particulate Matter Removal

Rapid social and industrial development has resulted in an increasing demand for fossil fuel energy, which increases particulate matter (PM) pollution. In this study, we employed a simple one-step electrospinning technique to fabricate polysulfone (PSF) fiber membranes for PM filtration. A 0.3 g/mL polymer solution with an N,N-dimethylformamide:tetrahydrofuran volume ratio of 3:1 yielded uniform and bead-free PSF fibers with a diameter of approximately 1.17 μm. The PSF fiber membrane exhibited excellent hydrophobicity and mechanical properties, including a tensile strength of 1.14 MPa and an elongation at break of 116.6%. Finally, the PM filtration performance of the PSF fiber membrane was evaluated. The filtration efficiencies of the membrane for PM2.5 and PM1.0 were approximately 99.6% and 99.2%, respectively. The pressure drops were 65.0 and 65.2 Pa, which were significantly lower than those of commercial air filters. Using this technique, PSF fiber membrane filters can be easily fabricated over a large area, which is promising for numerous air filtration systems.

Biomaterials and bioelectronics for self-powered neurostimulation

Self-powered neurostimulation via biomaterials and bioelectronics innovation has emerged as a compelling approach to explore, repair, and modulate neural systems. This review examines the application of self-powered bioelectronics for electrical stimulation of both the central and peripheral nervous systems, as well as isolated neurons. Contemporary research has adeptly harnessed biomechanical and biochemical energy from the human body, through various mechanisms such as triboelectricity, piezoelectricity, magnetoelasticity, and biofuel cells, to power these advanced bioelectronics. Notably, these self-powered bioelectronics hold substantial potential for delivering neural stimulations that are customized for the treatment of neurological diseases, facilitation of neural regeneration, and the development of neuroprosthetics. Looking ahead, we expect that the ongoing advancements in biomaterials and bioelectronics will drive the field of self-powered neurostimulation toward the realization of more advanced, closed-loop therapeutic solutions, paving the way for personalized and adaptable neurostimulators in the coming decades.

Hyperstable Eutectic Core-Spun Fiber Enabled Wearable Energy Harvesting and Personal Thermal Management Fabric

Electronic textiles have gradually evolved into one of the most important mainstays of flexible electronics owing to their good wearability. However, textile multifunctionality is generally achieved by stacking functional modules, which is not conducive to wearability. Integrating these modules into a single fiber provides a better solution. In this work, a core-spun functional fiber (CSF) constructed from hyper-environmentally stable Zn-based eutectogel as the core layer and polytetrafluoroethylene as the sheath is designed. The CSF achieves a synergistic output effect of piezoelectricity-enhanced triboelectricity, as well as reliable hydrophobicity, and high mid-infrared emissivity and visible light reflectivity. A monolayer functionalized integrated textile is woven from the CSF to enable effective energy (mechanical and droplet energy) harvesting and personal thermal management functions. Furthermore, scenarios for the energy supply, motion detection, and outdoor use of electronic fabrics for electronics applications are demonstrated, opening new avenues for the functional integration of electronic textiles.

The Rise of Electroactive Materials in Face Masks for Preventing Virus Infections

Air-transmitted pathogens may cause severe epidemics, posing considerable threats to public health and safety. Wearing a face mask is one of the most effective ways to prevent respiratory virus infection transmission. Especially since the new coronavirus pandemic, electroactive materials have received much attention in antiviral face masks due to their highly efficient antiviral capabilities, flexible structural design, excellent sustainability, and outstanding safety. This review first introduces the mechanism for preventing viral infection or the inactivation of viruses by electroactive materials. Then, the applications of electrostatic-, conductive-, triboelectric-, and microbattery-based materials in face masks are described in detail. Finally, the problems of various electroactive antiviral materials are summarized, and the prospects for their future development directions are discussed. In conclusion, electroactive materials have attracted great attention for antiviral face masks, and this review will provide a reference for materials scientists and engineers in antiviral materials and interfaces.

Tracing the Flu Symptom Progression via a Smart Face Mask

Respiration and body temperature are largely influenced by the highly contagious influenza virus, which poses persistent global public health challenges. Here, we present a wireless all-in-one sensory face mask (WISE mask) made of ultrasensitive fibrous temperature sensors. The WISE mask shows exceptional thermosensitivity, excellent breathability, and wearing comfort. It offers highly sensitive body temperature monitoring and respiratory detection capabilities. Capitalizing on the advances in the Internet of Things and artificial intelligence, the WISE mask is further demonstrated by customized flexible circuitry, deep learning algorithms, and a user-friendly interface to continuously recognize the abnormalities of both the respiration and body temperature. The WISE mask represents a compelling approach to tracing flu symptom progression in a cost-effective and convenient manner, serving as a powerful solution for personalized health monitoring and point-of-care systems in the face of ongoing influenza-related public health concerns.

Recent Progress of Advanced Materials for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) have received intense attention due to their broad application prospects in the new era of internet of things (IoTs) as distributed power sources and self-powered sensors. Advanced materials are vital components for TENGs, which decide their comprehensive performance and application scenarios, opening up the opportunity to develop efficient TENGs and expand their potential applications. In this review, a systematic and comprehensive overview of the advanced materials for TENGs is presented, including materials classifications, fabrication methods, and the properties required for applications. In particular, the triboelectric, friction, and dielectric performance of advanced materials is focused upon and their roles in designing the TENGs are analyzed. The recent progress of advanced materials used in TENGs for mechanical energy harvesting and self-powered sensors is also summarized. Finally, an overview of the emerging challenges, strategies, and opportunities for research and development of advanced materials for TENGs is provided.

Fibrous wearable and implantable bioelectronics

Fibrous wearable and implantable devices have emerged as a promising technology, offering a range of new solutions for minimally invasive monitoring of human health. Compared to traditional biomedical devices, fibers offer a possibility for a modular design compatible with large-scale manufacturing and a plethora of advantages including mechanical compliance, breathability, and biocompatibility. The new generation of fibrous biomedical devices can revolutionize easy-to-use and accessible health monitoring systems by serving as building blocks for most common wearables such as fabrics and clothes. Despite significant progress in the fabrication, materials, and application of fibrous biomedical devices, there is still a notable absence of a comprehensive and systematic review on the subject. This review paper provides an overview of recent advancements in the development of fibrous wearable and implantable electronics. We categorized these advancements into three main areas: manufacturing processes, platforms, and applications, outlining their respective merits and limitations. The paper concludes by discussing the outlook and challenges that lie ahead for fiber bioelectronics, providing a holistic view of its current stage of development.

Optimization of PVDF-TrFE Based Electro-Conductive Nanofibers: Morphology and In Vitro Response

In this study, morphology and in vitro response of electroconductive composite nanofibers were explored for biomedical use. The composite nanofibers were prepared by blending the piezoelectric polymer poly(vinylidene fluoride-trifluorethylene) (PVDF-TrFE) and electroconductive materials with different physical and chemical properties such as copper oxide (CuO), poly(3-hexylthiophene) (P3HT), copper phthalocyanine (CuPc), and methylene blue (MB) resulting in unique combinations of electrical conductivity, biocompatibility, and other desirable properties. Morphological investigation via SEM analysis has remarked some differences in fiber size as a function of the electroconductive phase used, with a reduction of fiber diameters for the composite fibers of 12.43% for CuO, 32.87% for CuPc, 36.46% for P3HT, and 63% for MB. This effect is related to the peculiar electroconductive behavior of fibers: measurements of electrical properties showed the highest ability to transport charges of methylene blue, in accordance with the lowest fibers diameters, while P3HT poorly conducts in air but improves charge transfer during the fiber formation. In vitro assays showed a tunable response of fibers in terms of viability, underlining a preferential interaction of fibroblast cells to P3HT-loaded fibers that can be considered the most suitable for use in biomedical applications. These results provide valuable information for future studies to be addressed at optimizing the properties of composite nanofibers for potential applications in bioengineering and bioelectronics.

Enhanced Filtration Efficiency of Natural Materials with the Addition of Electrospun Poly(vinylidene fluoride-co-hexafluoropropylene) Fibres

Pollutants and infectious diseases can spread through air with airborne droplets and aerosols. A respiratory mask can decrease the amount of pollutants we inhale and it can protect us from airborne diseases. With the onset of the COVID-19 pandemic, masks became an everyday item used by a lot of people around the world. As most of them are for a single use, the amount of non-recyclable waste increased dramatically. The plastic from which the masks are made pollutes the environment with various chemicals and microplastic. Here, we investigated the time- and size-dependent filtration efficiency (FE) of aerosols in the range of 25.9 to 685.4 nm of five different natural materials whose FE was enhanced using electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) fibres. A scanning electron microscope (SEM) was used to determine the morphology and structure of the natural materials as well as the thickness of the PVDF fibres, while the phase of the electrospun fibres was determined by Raman spectroscopy. A thin layer of the electrospun PVDF fibres with the same grammage was sandwiched between two sheets of natural materials, and their FE increased up to 80%. By varying the grammature of the electrospun polymer, we tuned the FE of cotton from 82.6 to 99.9%. Thus, through the optimization of the grammage of the electrospun polymer, the amount of plastic used in the process can be minimized, while achieving sufficiently high FE.

Efficient, Breathable and Biodegradable Filter Media for Face Masks

The global outbreak of COVID-19 results in the surge of disposable sanitary supplies, especially personal protective face masks. However, the charge dissipation of the electret meltblown nonwovens, which predominate in the commercial face mask filters, confines the durability and safety of commercial face masks. Furthermore, most of the face masks are made from nondegradable materials (such as PP) or part of their degradation products are toxic and contaminative to the environment. Herein, a type of face mask with biodegradable and highly effective PLA bi-layer complex fibrous membrane as filter core is reported. The prepared PLA complex membrane possesses a high-filtration efficiency of 99.1% for PM0.3 while providing a favorable pressure drop of 93.2 Pa. With the PLA complex membrane as the filter core, our face mask exhibits comparable or even higher wearability to commercial face masks, which further manifests our designed PLA complex membrane a promising filter media for face masks.