Construction of Vine-Inspired Antimicrobial Filter with Multiscale 3D Nanonetwork for High-Efficiency Air Filtration.

Enhancing the antimicrobial activity of high-efficiency particulate air (HEPA) filters while maintaining filtration efficiency and pressure drop is currently an urgent issue for preventing the spread of pathogenic microorganisms. Herein, inspired by vines which can enwind fences to fix as well as decorate them, a flexible antimicrobial chitin nanofiber (ChNF@CuOx) was fabricated and loaded onto the rigid glass fiber (GF) skeleton of a HEPA filter. Through the physical interaction, ChNF@CuOx was spontaneously enwound on GF, and ChNF@CuOx itself interweaved to form a new nanonetwork between the GF skeleton. The obtained antimicrobial air filter (ChNF@CuOx/GF) with a unique nanonetwork increased the filtration efficiency of the HEPA filter. Meanwhile, it possessed excellent inactivation ability against Staphylococcus aureus, Escherichia coli, and Candida albicans due to the urchin-like in situ grown CuOx on the ChNF. In particular, the oxygen vacancies generated unexpectedly in CuOx enabled it to produce reactive oxygen species. After eight cycles of antimicrobial assays, the antimicrobial rates of bacteria were higher than 99.5%, and those of fungi were greater than 98.3%. The successful synthesis of antimicrobial fibers and the construction of multidimensional nanoscale structures through a simple postprocessing method provide a new design mentality for antimicrobial functionalization for HEPA filters.

Chitin/Chitosan Nanofibers Toward a Sustainable Future: From Hierarchical Structural Regulation to Functionalization Applications.

Owing to its multiple fascinating properties of renewability, biodegradability, biocompatibility, and antibacterial activity, chitin is expected to become a green cornerstone of next-generation functional materials. Chitin nanofibers, as building blocks, form multiscale hierarchical structures spanning nano- and macrolevels in living organisms, which pave the way for sophisticated functions. Therefore, from a biomimetic perspective, exploiting chitin nanofibers for use in multifunctional, high-performance materials is a promising approach. Here, we first summarize the latest advances in the multiscale hierarchical structure assembly mode of chitin and its derivative nanofibers, including top-down exfoliation and bottom-up synthesis. Subsequently, we emphasize the environmental impacts of these methods, which are crucial for whether chitin nanofibers can truly contribute to a more eco-friendly era. Furthermore, the latest progress of chitin nanofibers in environmental and medical applications is also discussed. Finally, the potential challenges and tailored solutions of chitin nanofibers are further proposed, covering raw material, structure, function, manufacturing, policies, etc.

Chitin nanofibers promote rhizobial symbiotic nitrogen fixation in Lotus japonicus.

Chitin, an N-acetyl-D-glucosamine polymer, has multiple functions in living organisms, including the induction of disease resistance and growth promotion in plants. In addition, chitin oligosaccharides (COs) are used as the backbone of the signaling molecule Nod factor secreted by soil bacteria rhizobia to establish a mutual symbiosis with leguminous plants. Nod factor perception triggers host plant responses for rhizobial symbiosis. In this study, the effects of chitins on rhizobial symbiosis were examined in the leguminous plants Lotus japonicus and soybean. Chitin nanofiber (CNF), retained with polymeric structures, and COs elicited calcium spiking in L. japonicus roots expressing a nuclear-localized cameleon reporter. Shoot growth and symbiotic nitrogen fixation were significantly increased by CNF but not COs in L.japonicus and soybean. However, treatments with chitin and cellulose nanofiber, structurally similar polymers to CNF, did not affect shoot growth and nitrogen fixation in L.japonicus. Transcriptome analysis also supported the specific effects of CNF on rhizobial symbiosis in L.japonicus. Although chitins comprise the same monosaccharides and nanofibers share similar physical properties, only CNF can promote rhizobial nitrogen fixation in leguminous plants. Taking the advantages on physical properties, CNF could be a promising material for improving legume yield by enhancing rhizobial symbiosis.

Utilization of Pickering emulsion stabilized by chitin nanofibers for improving water and oxygen resistance of gelatin films.

The hydrophilicity of gelatin films obviously limits their application. In this work, novel protonated chitin nanofiber was prepared with green methods, surficial deacetylation combined with acidic and mechanical treatment. Composite films with excellent water and oxygen barrier properties were successfully prepared by blending O/W Pickering emulsions stabilized by chitin nanofibers with gelatin substrates. The films were characterized by Fourier-transform infrared, X-ray diffraction, mechanical properties, water and oxygen permeability, moisture content, water solubility, water contact angle and optical properties. The results demonstrated that the amino groups of chitin nanofibers bound to the carboxyl groups of gelatin via electrostatic interactions, which contributing to the excellent mechanical and barrier properties of composite films. The elongation at break of composite film (the concentration of chitin nanofiber was 0.2 wt%) was 2.66 times of gelatin film. And the water vapor and oxygen permeability of composite films lowered to 65.9 % and 52.9 %, respectively. The introduction of O/W Pickering emulsion significantly enhanced the hydrophobicity of gelatin-based film and the chitin nanofibers played a positive role in stabilizing the gelatin chains to a certain extent. This study expands the application fields of gelatin-based films and provides valuable technical route for the preparation of barrier films.

Biodegradable chitin nanofiber-alginate dialdehyde hydrogel: An injectable, self-healing scaffold for anti-tumor drug delivery.

Injectable hydrogels fabricated from natural polymers have attracted increasing attentions for their potential in biomedical application owing to the biocompatibility and biodegradability. A new class of natural polymer based self-healing hydrogel is constructed through dynamic covalent bonds. The injectable self-healing hydrogels are fabricated by introducing alginate aldehyde to form Schiff base bonds with the chitin nanofibers. These hydrogels demonstrate excellent self-healing properties, injectability, and pH-responsive sol-gel transition behaviors. As a result, they can serve as carriers to allow an effective encapsulation of doxorubicin (DOX) for drug delivery. Furthermore, these hydrogels exhibit excellent biocompatibility and degradability in vitro and in vivo. The sustained release of DOX from the hydrogels effectively suppresses tumor growth in animal models without causing significant systemic toxicity, suggesting their potential application in anti-tumor therapies.

A Mini-Review: Fabrication of Polysaccharide Composite Materials Based on Self-Assembled Chitin Nanofibers.

This mini-review presents the fabrication methods for polysaccharide composite materials that employ self-assembled chitin nanofibers (ChNFs) as functional components. Chitin is one of the most abundant polysaccharides in nature. However, it is mostly not utilized because of its poor feasibility and processability. Self-assembled ChNFs are efficiently obtained by a regenerative bottom-up process from chitin ion gels using an ionic liquid, 1-allyl-3-methylimodazolium bromide. This is accomplished by immersing the gels in methanol. The resulting dispersion is subjected to filtration to isolate the regenerated materials, producing ChNF films with a morphology defined by highly entangled nanofibers. The bundles are disintegrated by electrostatic repulsion among the amino groups on the ChNFs in aqueous acetic acid to produce thinner fibers known as scaled-down ChNFs. The self-assembled and scaled-down ChNFs are combined with other chitin components to fabricate chitin-based composite materials. ChNF-based composite materials are fabricated through combination with other polysaccharides.

Cryomilling-assisted high purity ß-chitin extraction from Uroteuthis edulis pens.

We report on the extraction of ß-chitin from pens (or Gladius) of Uroteuthis edulis, a squid species prevalent in the Pacific coastal regions of East Asia. In particular, we employ cryogenic mechanical grinding (or cryomilling) as a pre-treatment process for the raw squid pens. We show that the cryomilling step enables an effective pulverization of the raw materials, which facilitates the removal of protein residues allowing the extraction of high-purity ß-chitin with a high acetylation degree (∼97 %) and crystallinity (∼82 %). We also demonstrate that the Uroteuthis edulis extract ß-chitin affords a free-standing film with excellent optical transmittance and mechanical properties.

Preparation of Chitin Nanofibers and Natural Rubber Composites and Their Triboelectric Nanogenerator Applications.

Triboelectric nanogenerators (TENGs) have gained significant attention as promising energy-harvesting devices that convert mechanical energy into electrical energy through charge separation induced by friction and electrostatic induction. In this study, we explore the utilization of biowaste shrimp shell-extracted chitin nanofiber (ChNF) as a viable eco-friendly material for TENG applications. Composite materials were prepared by incorporating ChNF into natural rubber (NRL) at loading levels of 0.1 and 0.2 wt% (NRL/ChNF) to form the TENG triboelectric layer. ChNFs with a uniform width of approximately 10-20 nm were successfully extracted from the shrimp shells through a simple mechanical procedure. The NRL/ChNF composites exhibited enhanced mechanical properties, as evidenced by a higher Young's modulus (3.4 GPa) compared to pure NRL. Additionally, the NRL/ChNF composites demonstrated an increased dielectric constant of 3.3 at 0.1 MHz. Moreover, the surface potential difference of NRL increased from 0.182 V to 1.987 V in the NRL/ChNF composite. When employed as the triboelectric layer in TENG, the NRL/ChNF composites exhibited significant improvement in their output voltage, with it reaching 106.04 ± 2.3 V. This enhancement can be attributed to the increased dielectric constant of NRL/ChNF, leading to enhanced charge exchange and charge density. This study presents a straightforward and environmentally friendly technique for preparing sustainable natural materials suitable for energy-harvesting devices.

Chitin nanofibrils assisted 3D printing all-chitin hydrogels for wound dressing.

The direct ink writing technique used in 3D printing technology is generally applied to designing biomedical hydrogels. Herein, we proposed a strategy for preparing all-chitin-based inks for wound dressing via direct ink writing technique. The ß-chitin nanofibers (MACNF) with a high aspect ratio were applied as a nanofiller to modulate the rheological properties of the alkaline dissolved chitin solution. The printing fidelity significantly depends on the MACNF introduction amount to the composite ink. 5-10 wt% MACNF ratio showed superior printing performance. The printed scaffold showed a uniform micron-sized pore structure and a woven network of nanofibers. Due to the good biocompatibility of chitin and the stereoscopic spatial skeleton, this scaffold showed excellent performance as a wound dressing, which can promote cell proliferation, collagen deposition and the angiogenesis of wounds, demonstrating its potential in biomedical applications. This approach successfully balanced the chitinous printability and biofunctions.

Smart nano-inks based on natural food colorant for screen-printing of dynamic shelf life of shrimp.

Intelligent packaging embedded with food freshness indicators can monitor food quality and be deployed for food safety and cutting food waste. The innovative nano-inks for dynamic shelf-life printing based on natural food colorant with application in real-time monitoring of shrimp freshness were prepared. Co-assembly of saffron petal anthocyanin (SPA) with hydrophobic curcumin (Cur) into chitin nano-scaffold (particle sizes around 26 ± 8 nm) could deliver hindering SPA leaching, confirmed by FT-IR, FE-SEM, AFM, and color stability test. The best response to pH-sensitivity was found in a ratio of (1:4) Cur/SPA (30% (v/w) in ChNFs that was correlated with the chemical and microbial changes of shrimp during shrimp freshness. However, smart screen-printed inks signified higher responsiveness to pH changes than FFI films. Therefore, smart-printed indicators introduced the excellent potential for a short response time, easy, cost-effective, eco-friendly, co-assembly, great color stabilities, and lifetime for nondestructively freshness monitoring foods and supplements.

Mussel-inspired chitin nanofiber adherable hydrogel sensor with interpenetrating network and great fatigue resistance for motion and acoustics monitoring.

A method for grafting dopamine onto TEMPO-oxidized chitin nanofibers (TOChN) was developed, achieving a surface grafting rate of 54 % through the EDC/NHS reaction. This process resulted in the formation of dopamine-grafted TOChN (TOChN-DA). Subsequently, an adherent, highly sensitive, fatigue-resistant conductive PAM/TOChN-PDA/Fe3+ (PTPF) hydrogel was successfully synthesized based on the composition of polyacrylamide (PAM) and TOChN-DA, which exhibited good cell compatibility, a tensile strength of 89.42 kPa, and a high adhesion strength of 62.56 kPa with 1.2 wt% TOChN-DA. Notably, the PTPF hydrogel showed stable adherence to various surfaces, such as rubber, copper, and human skin. Specifically, the addition of FeCl3 contributed to a multifunctional design in the PTPF interpenetrating network (IPN) hydrogel, endowing it with conductivity, cohesion, and antioxidant properties, which facilitated sensitive motion and acoustics monitoring. Moreover, the PTPF hydrogel demonstrated exceptional fatigue resistance and sensing stability, maintaining performance at 50 % strain over 1000 cycles. These attributes render the PTPF hydrogel a promising candidate for advanced biosensors in medical and athletic applications.

Promoting microbial fermentation in lignocellulosic hydrolysates by removal of inhibitors using MTES and PEI-modified chitosan-chitin nanofiber hybrid aerogel.

To further enhance the removal efficiency for furanic and phenolic compounds in lignocellulosic hydrolysates, a new detoxification strategy was proposed, which retained fermentable sugars and promoted the growth and metabolism of subsequent bacteria. The best adsorbent (P/M-CCA) was prepared by hybrid chitosan-chitin nanofiber, graft modification with polyethylenimine, and silanization with methyl triethoxylsilane in order. Taken corn cob hydrolysate as object, the removal rates of HMF and furfural were 85.1 % and 99.0 %, respectively. The removal rates of six out of nine phenolic inhibitors were 100 %, and the other three were more than 65 %. Even better, the retention rates of glucose and xylose were both 100 %. In contrast to no growth in undetoxified hydrolysates, Bacillus coagulans grew normally in detoxified hydrolysates, and lactic acid reached 19.1 g/L after 12 h fermentation. P/M-CCA achieves both removal of multiple inhibitors and retain sugars, which would promote the valorization of highly toxic lignocellulosic hydrolysates.

Magnetic macroporous chitin microsphere as a support for covalent enzyme immobilization.

In this study, a novel magnetic macroporous chitin microsphere (MMCM) was developed for enzyme immobilization. Chitin nanofibers were prepared and subsequently subjected to self-assembly with magnetic nanoparticles and PMMA (polymethyl methacrylate). Following this, microspheres were formed through spray drying, achieving a porous structure through etching. The MMCM serves as an effective support for immobilizing enzymes, allowing for their covalent immobilization both on the microsphere's surface and within its pores. The substantial surface area resulting from the porous structure leads to a 2.1-fold increase in enzyme loading capacity compared to non-porous microspheres. The MMCM enhances stability of the immobilized enzymes under various pH and temperature conditions. Furthermore, after 20 days of storage at 4 °C, the residual activity of the immobilized enzyme was 2.93 times that of the free enzyme. Even after being recycled 10 times, the immobilized enzyme retained 56.7 % of its initial activity. It's noteworthy that the active sites of the enzymes remained unchanged after immobilization using the MMCM, and kinetic analysis revealed that the affinity of the immobilized enzymes rivals that of the free enzymes.

Enhanced stabilization of multifunctional phenolic acids-grafted chitin nanofibers for Pickering emulsions.

The objective of this study was to develop novel functional stabilizers for Pickering emulsions using phenolic acids-grafted chitin nanofibers (phenolic acids-g-ChNF), which were fabricated by grafting ferulic acid (FA), sinapic acid (SA) and caffeic acid (CA) onto ChNF via free radical-mediated method. The Fourier transform infrared spectrum and Proton nuclear magnetic resonance showed that graft copolymerization occurred between the amino groups of ChNF and the carbonyl of the phenolic acids. Further, it was revealed that CA-g-ChNF and SA-g-ChNF possessed stronger antioxidant and antibacterial properties than the original ChNF and FA-g-ChNF. Additionally, we applied phenolic acids-g-ChNF to develop Pickering emulsions and found that SA-g-ChNF- and CA-g-ChNF-stabilized emulsions displayed reduced droplet sizes compared to FA, the main reason for which was that SA and CA had a rather close bonding relationship with ChNF. Taken together, SA-g-ChNF and CA-g-ChNF as novel multi-functional particles can be employed for facilitating the stability of Pickering emulsions.

Surface modification of chitin nanofibers with dopamine as efficient nanosorbents for enhanced removal of dye pollution and metal ions.

The development of environmentally friendly and low-cost adsorbents with high adsorption capacity remains a challenge. Herein, chitin nanofiber-polydopamine composite materials (CNDA) have been obtained by surface modification of chitin nanofiber using dopamine. According to the results of transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), and X-ray photoelectron spectrometer (XPS), polydopamine have been successfully coated on the surface of chitin nanofiber (ChNF). The ability to remove methylene blue (MB) has been analyzed via standard adsorption experiments, indicating that the maximum adsorption capacity (qmax) can reach 196.6 mg/g at MB initial concentration of 50 mg/L. Most importantly, the adsorption kinetics, isotherm, and thermodynamics were used to investigate the MB adsorption mechanism on composites. This indicated that the polydopamine on the surface of chitin nanofiber (ChNF) plays an important role in the MB dye adsorption. Moreover, the removal ability of CNDA to metal ions has also been investigated, indicating high capacities for Fe3+, Mn2+, Cu2+, and Ni2+. Based on their biodegradability and good adsorption capacity, the CNDA composite material can be considered a promising adsorbent for wastewater treatment.

Production of copper nanoparticle-immobilized chitin nanofibers and their role in plant disease control.

Chitin is used in agriculture to improve crop production; however, its use is limited due to difficulties in its handling. A chitin nanofiber (CNF) overcomes this issue and, due to its elicitor activity, has great potential for crop protection. To expand CNF utilization, a copper nanoparticles-based antimicrobic CNF (CuNPs/CNF) was prepared using a chemical reduction method. The formation of CuNPs was confirmed via scanning electron microscopy. Thermogravimetric analysis revealed that the amount of CuNPs on the CNF was dose-dependent on the precursor salt, copper acetate. CuNPs endowed the CNF with strong antimicrobial activity against Alternaria brassicicola and Pectobacterium carotovorum. Moreover, the CuNPs/CNF reduced pathogen infection in cabbage. The antimicrobial activity and disease prevention of the CuNPs/CNF was increased compared to the corresponding CNF or commercial agrochemical Bordeaux treatment. These results indicate that CuNPs conferred antimicrobial activity on the CNF and increased the efficacy of plant disease protection.

Thixotropic ß-Chitin Nanofiber Hydrogel with a Living Body-Responsive Self-Hardening Property and Its Application as a Sprayable Antiadhesion Barrier.

Considering recent advances in surgical techniques, sprayable antiadhesion barriers that are compatible with minimally invasive procedures are needed. However, the relatively low mechanical stiffness of the current thixotropic reversible sol-to-gel transition hydrogels has hindered their medical application. Herein, we show a thixotropic sprayable ß-chitin nanofiber hydrogel that spontaneously lost the thixotropic property in response to the environments within the living body. Furthermore, interactions between hydrogels and the biological environment result in a significant increase in mechanical stiffness. Due to these advantageous properties, ß-chitin nanofiber hydrogels administered by spray prevent postoperative abdominal adhesions and are thus promising sprayable antiadhesion barriers.

pH-sensitive cellulose/chitin nanofibrillar hydrogel for dye pollutant removal.

In this study, a pH-sensitive smart hydrogel was successfully prepared by combining a polyelectrolyte complex using biopolymeric nanofibrils. By adding a green citric acid cross-linking agent to the formed chitin and cellulose-derived nanofibrillar polyelectrolytic complex, a hydrogel with excellent structural stability could be prepared even in a water environment, and all processes were conducted in an aqueous system. The prepared biopolymeric nanofibrillar hydrogel not only enables rapid conversion of swelling degree and surface charge according to pH but can also effectively remove ionic contaminants. The ionic dye removal capacity was 372.0 mg/g for anionic AO and 140.5 mg/g for cationic MB. The surface charge conversion ability according to pH could be easily applied to the desorption of the removed contaminants, and as a result, it showed an excellent contaminant removal efficiency of 95.1 % or more even in the repeated reuse process 5 times. Overall, the eco-friendly biopolymeric nanofibrillar pH-sensitive hydrogel shows potential for complex wastewater treatment and long-term use.

Chitin-Derived Nitrogen-Doped Carbon Nanopaper with Subwavelength Nanoporous Structures for Solar Thermal Heating.

Sustainable biomass-derived carbons have attracted research interest because of their ability to effectively absorb and convert solar light to thermal energy, a phenomenon known as solar thermal heating. Although their carbon-based molecular and nanoporous structures should be customized to achieve enhanced solar thermal heating performance, such customization has insufficiently progressed. In this study, we transformed a chitin nanofiber/water dispersion into paper, referred to as chitin nanopaper, with subwavelength nanoporous structures by spatially controlled drying, followed by temperature-controlled carbonization without any pretreatment to customize the carbon-based molecular structures. The optimal carbonization temperature for enhancing the solar absorption and solar thermal heating performance of the chitin nanopaper was determined to be 400 °C. Furthermore, we observed that the nitrogen component, which afforded nitrogen-doped carbon structures, and the high morphological stability of chitin nanofibers against carbonization, which maintained subwavelength nanoporous structures even after carbonization, contributed to the improved solar absorption of the carbonized chitin nanopaper. The carbonized chitin nanopaper exhibited a higher solar thermal heating performance than the carbonized cellulose nanopaper and commercial nanocarbon materials, thus demonstrating significant potential as an excellent solar thermal material.

Highly stretchable, tough and conductive chitin nanofiber composite hydrogel as a wearable sensor.

To meet the requirements of eco-friendly and sustainability in the 21st century, hydrogels based on biopolymer with conductivity and stretchable property have attained increasing attention for strain sensor. However, the as-prepared of hydrogel sensor with excellent mechanical property and high strain sensitivity is still a challenge. In this study, chitin nanofiber (ChNF) reinforced composite hydrogels of PACF are fabricated via a facile one-pot method. The obtained PACF composite hydrogel exhibits good transparency (80.6 % at 800 nm)and excellent mechanical properties (tensile strength, 261.2 kPa; tensile strain as high as 550.3 %). Moreover, the composite hydrogels also demonstrate excellent anti-compression performance. The composite hydrogels own good conductivity (1.20 S/m) and strain sensitivity. Most importantly, the hydrogel can be assembled as a strain/pressure sensor for detecting large-scale and small-scale human motion. Therefore, flexible conductive hydrogel strain sensors will have broad application prospects in artificial intelligence, electronic skin, and personal health.