Bioinspired Structures Made of Silicone Nanofilaments for Upcycling Waste Masks to Reusable N95 Respirators.

The increasing demand for personal protective equipment such as single-use masks has led to large amounts of nondegradable plastic waste, aggravating economic and environmental burdens. This study reports a simple and scalable approach for upcycling waste masks via a chemical vapor deposition technique, realizing a trichome-like biomimetic (TLB) N95 respirator with superhydrophobicity (water contact angle ≥150°), N95-level protection, and reusability. The TLB N95 respirator comprising templated silicone nanofilaments with an average diameter of ∼150 nm offers N95-level protection and breathability comparable to those of commercial N95 respirators. The TLB N95 respirator can still maintain its N95-level protection against particulate matter and viruses after 10 disinfection treatment cycles (i.e., ultraviolet irradiation, microwave irradiation, dry heating, and autoclaving), demonstrating durable reusability. The proposed strategy provides new insight into upcycle waste masks, breaking the existing design and preparation concept of reusable masks.

Trichome-Like Biomimetic Air Filters via Templated Silicone Nanofilaments.

Air pollution threats to human health have increased awareness of the role of filter units in air cleaning applications. As an ideal energy-saving strategy for air filters, the slip effect on nanofiber surfaces can potentially overcome the trade-off between filtration efficiency and pressure drop. However, the potential of the slip effect in nanofibrous structures is significantly limited by the tight nanofiber stacks. In this study, trichome-like biomimetic (TLB) air filters with 3D-templated silicone nanofilaments (average diameter: ≈74 nm) are prepared based on an in situ chemical vapor deposition (CVD) method inspired by plant purification. Theoretical modeling and experimental results indicate that TLB air filters make significant use of the slip effect to overcome the efficiency-resistance tradeoff. The selectable filter class (up to U15, ≈99.9995%) allows TLB air filters to meet various requirements, and their integral filtration performance surpasses that of most commodity air filters, including melt-blown cloth, ePTFE membranes, electrospun mats, and glass fiber paper. The proposed strategy directly transforms commercial filter media and filters into TLB air filters using a bottom-up, one-step approach. As a proof-of-concept, reusable N95 respirators and air purifiers equipped with TLB air filters are fabricated, overcoming the limitations of existing filter designs and fabrication methods.

Additive Manufacturing of Nanocellulose Aerogels with Structure-Oriented Thermal, Mechanical, and Biological Properties.

Additive manufacturing (AM) is widely recognized as a versatile tool for achieving complex geometries and customized functionalities in designed materials. However, the challenge lies in selecting an appropriate AM method that simultaneously realizes desired microstructures and macroscopic geometrical designs in a single sample. This study presents a direct ink writing method for 3D printing intricate, high-fidelity macroscopic cellulose aerogel forms. The resulting aerogels exhibit tunable anisotropic mechanical and thermal characteristics by incorporating fibers of different length scales into the hydrogel inks. The alignment of nanofibers significantly enhances mechanical strength and thermal resistance, leading to higher thermal conductivities in the longitudinal direction (65 mW m-1  K-1 ) compared to the transverse direction (24 mW m-1  K-1 ). Moreover, the rehydration of printed cellulose aerogels for biomedical applications preserves their high surface area (≈300 m2  g-1 ) while significantly improving mechanical properties in the transverse direction. These printed cellulose aerogels demonstrate excellent cellular viability (>90% for NIH/3T3 fibroblasts) and exhibit robust antibacterial activity through in situ-grown silver nanoparticles.

Biomimetic Light-Driven Aerogel Passive Pump for Volatile Organic Pollutant Removal.

Inspired by the solar-light-driven oxygen transportation in aquatic plants, a biomimetic sustainable light-driven aerogel pump with a surface layer containing black manganese oxide (MnO2 ) as an optical absorber is developed. The flow intensity of the pumped air is controlled by the pore structure of nanofilbrillated cellulose, urea-modified chitosan, or polymethylsilsesquioxane (PMSQ) aerogels. The MnO2 -induced photothermal conversion drives both the passive gas flow and the catalytic degradation of volatile organic pollutants. All investigated aerogels demonstrate superior pumping compared to benchmarked Knudsen pump systems, but the inorganic PMSQ aerogels provide the highest flexibility in terms of the input power and photothermal degradation activity. Aerogel light-driven multifunctional gas pumps offer a broad future application potential for gas-sensing devices, air-quality mapping, and air quality control systems.

Additive manufacturing of silica aerogels.

Owing to their ultralow thermal conductivity and open pore structure1-3, silica aerogels are widely used in thermal insulation4,5, catalysis6, physics7,8, environmental remediation6,9, optical devices10 and hypervelocity particle capture11. Thermal insulation is by far the largest market for silica aerogels, which are ideal materials when space is limited. One drawback of silica aerogels is their brittleness. Fibre reinforcement and binders can be used to overcome this for large-volume applications in building and industrial insulation5,12, but their poor machinability, combined with the difficulty of precisely casting small objects, limits the miniaturization potential of silica aerogels. Additive manufacturing provides an alternative route to miniaturization, but was "considered not feasible for silica aerogel"13. Here we present a direct ink writing protocol to create miniaturized silica aerogel objects from a slurry of silica aerogel powder in a dilute silica nanoparticle suspension (sol). The inks exhibit shear-thinning behaviour, owing to the high volume fraction of gel particles. As a result, they flow easily through the nozzle during printing, but their viscosity increases rapidly after printing, ensuring that the printed objects retain their shape. After printing, the silica sol is gelled in an ammonia atmosphere to enable subsequent processing into aerogels. The printed aerogel objects are pure silica and retain the high specific surface area (751 square metres per gram) and ultralow thermal conductivity (15.9 milliwatts per metre per kelvin) typical of silica aerogels. Furthermore, we demonstrate the ease with which functional nanoparticles can be incorporated. The printed silica aerogel objects can be used for thermal management, as miniaturized gas pumps and to degrade volatile organic compounds, illustrating the potential of our protocol.

Flexible and Ultrathin Waterproof Cellular Membranes Based on High-Conjunction Metal-Wrapped Polymer Nanofibers for Electromagnetic Interference Shielding.

Ultrathin, lightweight, and flexible electromagnetic interference (EMI) shielding materials are urgently demanded to address EM radiation pollution. Efficient design to utilize the shields' microstructures is crucial yet remains highly challenging for maximum EMI shielding effectiveness (SE) while minimizing material consumption. Herein, novel cellular membranes are designed based on a facile polydopamine-assisted metal (copper or silver) deposition on electrospun polymer nanofibers. The membranes can efficiently exploit the high-conjunction cellular structures of metal and polymer nanofibers, and their interactions for excellent electrical conductivity, mechanical flexibility, and ultrahigh EMI shielding performance. EMI SE reaches more than 53 dB in an ultra-broadband frequency range at a membrane thickness of merely 2.5 µm and a density of 1.6 g cm-3 , and an SE of 44.7 dB is accomplished at the lowest thickness of 1.2 µm. The normalized specific SE is up to 232 860 dB cm2 g-1 , significantly surpassing that of other shielding materials ever reported. More, integrated functionalities are discovered in the membrane, such as antibacterial, waterproof properties, excellent air permeability, high resistance to mechanical deformations and low-voltage uniform heating performance, offering strong potential for applications in aerospace and portable and wearable smart electronics.