Bio-Based Artificial Nacre with Excellent Mechanical and Barrier Properties Realized by a Facile In Situ Reduction and Cross-Linking Reaction

Supertough MXene/Sodium Alginate Composite Fiber Felts Integrated with Outstanding Electromagnetic Interference Shielding and Heating Properties

The development of multifunctional MXene-based fabrics for smart textiles and portable devices has garnered significant attention. However, very limited studies have focused on their structure design and associated mechanical properties. Here, the supertough MXene fiber felts composed of MXene/sodium alginate (SA) fibers were fabricated. The fracture strength and bending stiffness of felts can be up to 97.8 MPa and 1.04 N mm2, respectively. Besides, the fracture toughness of felts was evaluated using the classic Griffith theory, yielding to a critical stress intensity factor of 1.79 M P a m . In addition, this kind of felt presents outstanding electrothermal conversion performance (up to 119 °C at a voltage of 2.5 V), high cryogenic and high-temperature tolerance of photothermal conversion performance (-196 to 160 °C), and excellent electromagnetic interference (EMI) shielding effectiveness (54.4 dB in the X-band). This work provides new structural design concepts for high-performance MXene-based textiles, broadening their future applications.

Self-Assembled Hydrogel Membranes with Structurally Tunable Mechanical and Biological Properties

Using supramolecular self-assembled nanocomposite materials made from protein and polysaccharide components is becoming more popular because of their unique properties, such as biodegradability, hierarchical structures, and tunable multifunctionality. However, the fabrication of these materials in a reproducible way remains a challenge. This study presents a new evaporation-induced self-assembly method producing layered hydrogel membranes (LHMs) using tropocollagen grafted by partially deacetylated chitin nanocrystals (CO-g-ChNCs). ChNCs help stabilize tropocollagen's helical conformation and fibrillar structure by forming a hierarchical microstructure through chemical and physical interactions. The LHMs show improved mechanical properties, cytocompatibility, and the ability to control drug release using octenidine dihydrochloride (OCT) as a drug model. Because of the high synergetic performance between CO and ChNCs, the modulus, strength, and toughness increased significantly compared to native CO. The biocompatibility of LHM was tested using the normal human dermal fibroblast (NHDF) and the human osteosarcoma cell line (Saos-2). Cytocompatibility and cell adhesion improved with the introduction of ChNCs. The extracted ChNCs are used as a reinforcing nanofiller to enhance the performance properties of tropocollagen hydrogel membranes and provide new insights into the design of novel LHMs that could be used for various medical applications, such as control of drug release in the skin and bone tissue regeneration.

A Strong, Tough, and Stable Composite with Nacre-Inspired Sandwich Structure

Improving the fracture resistance of nacre-inspired composites is crucial in addressing the strength-toughness trade-off. However, most previously proposed strategies for enhancing fracture resistance in these composites have been limited to interfacial modification by polymer, which restricts mechanical enhancement. Here, a composite material consisting of graphene oxide (GO) lamellae and nanocrystalline reinforced amorphous alumina nanowires (NAANs) has been developed. The structure of the composite is inspired by nacre and is composed of stacked GO nanosheets with NAANs in between, forming a sandwich-like structure. This design enhances the fracture resistance of the composite through the pull-out of GO nanosheets at the nanoscale and GO/NAANs sandwich-like coupling at the micro-scale, while also providing stiff ceramic support. This composite simultaneously possesses high strength (887.8 MPa), toughness (31.6 MJ m-3), superior cyclic stability (1600 cycles), and long-term (2 years) immersion stability, which outperform previously reported GO-based lamellar composites. The hierarchical fracture design provides a new path to design next-generation strong, tough, and stable materials for advanced engineering applications.

Scalable Production of 2D Minerals by Polymer Intercalation and Adhesion for Multifunctional Applications

Natural and sustainable 2D minerals have many unique properties and may reduce reliance on petroleum-based products. However, the large-scale production of 2D minerals remains challenging. Herein, a green, scalable, and universal polymer intercalation and adhesion exfoliation (PIAE) method to produce 2D minerals such as vermiculite, mica, nontronite, and montmorillonite with large lateral sizes and high efficiency, is developed. The exfoliation relies on the dual functions of polymers involving intercalation and adhesion to expand interlayer space and weaken interlayer interactions of minerals, facilitating their exfoliation. Taking vermiculite as an example, the PIAE produces 2D vermiculite with an average lateral size of 1.83 ± 0.48 µm and thickness of 2.40 ± 0.77 nm at a yield of ≈30.8%, surpassing state-of-the-art methods in preparing 2D minerals. Flexible films are directly fabricated by the 2D vermiculite/polymer dispersion, exhibiting outstanding performances including mechanical strength, thermal resistance, ultraviolet shielding, and recyclability. The representative application of colorful multifunctional window coatings in sustainable buildings is demonstrated, indicating the potential of massively produced 2D minerals.

Molecular Orientation-Regulated Bioinspired Multilayer Composites with Largely Enhanced Mechanical Properties

Natural nacre's hierarchical brick-and-mortar architecture motivates intensive studies on inorganic platelet/polymer multilayer composites, targeting mechanical property enhancement only by two strategies: optimizing the size and alignment of inorganic platelets and improving the interfacial interaction between inorganic platelets and polymers. Herein, a new strategy of polymer chain orientation to enhance the property of bioinspired multilayered composites is presented, which facilitates more stress to be transferred from polymer layers to inorganic platelets by simultaneous stiffening of multiple polymer chains. To this end, bioinspired multilayer films consisting of oriented sodium carboxymethyl cellulose chains and alumina platelets are designed and fabricated by three successive steps of water evaporation-induced gelation in glycerol, high-ratio prestretching, and Cu²⁺ infiltration. Regulating the orientation state of sodium carboxymethyl cellulose leads to a large enhancement of mechanical properties, including Young's modulus (2.3 times), tensile strength (3.2 times), and toughness (2.5 times). It is observed experimentally and predicted theoretically that the increased chain orientation induces failure mode transition in the multilayered films from alumina platelet pull-out to alumina platelet fracture because more stress is transferred to the platelets. This strategy opens an avenue toward rational design and manipulation of polymer aggregation states in inorganic platelet/polymer multilayer composites and allows a highly effective increase in modulus, strength, and toughness.

Strong and Tough Nacre-Inspired Graphene Oxide Composite with Hierarchically Similar Structure

We report a graphene oxide (GO)-based composite, featuring GO/cross-linking agent (CA) nanoparticles, inspired by a nacre-like hierarchical structure present in nature. The as-prepared GO/CA composite was powdered to nanoscale particles and then mixed with pure GO to be GO/CA/GO (GCG) composite forming hierarchical GO/CA nanoasperities on the GO surface. The strength and toughness of the nacre-inspired GCG composite films were simultaneously improved by adjusting the nanoparticle concentration and hierarchical level of the GO-based films. Compared to pristine GO films and GO/CA composites, which exhibit a low level of hierarchy in their structures, the tensile strength and toughness of the GCG composites with higher hierarchy were enhanced 3.1 and 1.6 times and 47.6 and 10.9 times, respectively. Furthermore, a plausible mechanism of increasing mechanical properties based on nanoscale asperities and homogeneous interactions between GO and CA has been discussed.

Development of photoluminescent artificial nacre-like nanocomposite from polyester resin and graphene oxide

Long-lasting phosphorescent nacre-like material was simply prepared from a nanocomposite of inorganic and organic materials. Low molecular weight unsaturated polyester (PET), graphene oxide (GO), and nanoparticles of rare-earth activated aluminate pigment were used in the preparation process of an organic/inorganic hybrid nanocomposite. Using methylethylketone peroxide (MEKP) as a hardener, we were able to develop a fluid solution that hardens within minutes at room temperature. Covalent and hydrogen bonds were introduced between the polyester resin and graphene oxide nanosheets. The interface interactions of those bonds resulted in toughness, excellent tensile strength, and high durability. The produced nacre substrates demonstrated long-persistent and reversible luminescence. The excitation of the produced nacre substrates at 365 nm resulted in a 524 nm emission. After being exposed to UV light, the photoluminescent nacre substrates became green. The increased superhydrophobic activity of the produced nacre substrates was achieved without affecting their physico-mechanical properties.

Quaternary Artificial Nacre-Based Electronic Textiles with Enhanced Mechanical and Flame-Retardant Performance

Interest in wearable electronics has led to extensive studies on woven textiles that are mechanically robust and stretchable, have high electrical conductivities, and exhibit fire resistance properties even at high temperatures. We demonstrate a highly easy and scalable method for fabricating defect-free graphene (dfG) nacre-based woven electronic textiles (e-textiles) with enhanced flame-retardant properties and high electronic conductivities. The as-prepared graphene shows perfect preservation of its inherent properties without any crystal damage during subsequent exfoliation and noncovalent melamine functionalization. The defect-free graphene functionalized by melamine (m-dfG) is well dispersed in various polar solvents. To investigate the synergistic effect of m-dfG, quaternary artificial nacre composites are fabricated by adding manganese(II) chloride to a m-dfG/polymer (carboxymethyl cellulose (CMC)) composite. Their mechanical, electrical, and thermal characteristics are then evaluated. The quaternary m-dfG-Mn²⁺-CMC artificial nacre exhibits exceptionally enhanced mechanical properties (tensile strength: 613.9 MPa; toughness: 7.13 MJ m^-3) and the best flame retardancy (even at torch heating) as compared to those of graphene oxide/reduced graphene oxide (GO/rGO)-based nacres. In this context, our approach will be helpful to future wearable electronics and fire-retardant textiles with high strength, which can accelerate the commercial viability of e-textiles.

Emerging Developments on Nanocellulose as Liquid Crystals: A Biomimetic Approach

Biomimetics is the field of obtaining ideas from nature that can be applied in science, engineering, and medicine. The usefulness of cellulose nanocrystals (CNC) and their excellent characteristics in biomimetic applications are exciting and promising areas of present and future research. CNCs are bio-based nanostructured material that can be isolated from several natural biomasses. The CNCs are one-dimensional with a high aspect ratio. They possess high crystalline order and high chirality when they are allowed to assemble in concentrated dispersions. Recent studies have demonstrated that CNCs possess remarkable optical and chemical properties that can be used to fabricate liquid crystals. Research is present in the early stage to develop CNC-based solvent-free liquid crystals that behave like both crystalline solids and liquids and exhibit the phenomenon of birefringence in anisotropic media. All these characteristics are beneficial for several biomimetic applications. Moreover, the films of CNC show the property of iridescent colors, making it suitable for photonic applications in various devices, such as electro-optical devices and flat panel displays.

Mechanically Strong Electrically Insulated Nanopapers with High UV Resistance Derived from Aramid Nanofibers and Cellulose Nanofibrils

Aramid nanofibers (ANFs) have great potential for civil and military applications due to their remarkable mechanical modulus, excellent chemical reliability, and superior thermostability. Unfortunately, the weak combination of neighboring ANFs limits the mechanical properties of ANF-based materials owing to their inherent rigidity and chemical inertness. Herein, high-performance nanopapers are fabricated by introducing a tiny amount of cellulose nanofibrils (CNFs) to serve as reinforcing blocks via vacuum filtration. As a result of the formation of nanosized building blocks and hydrogen-bonding interaction of CNFs, the resultant ANF/CNF nanopaper yields a record-high tensile strength (406.43 ± 16.93 MPa) and toughness (86.13 ± 5.22 MJ m^-3), which are 1.8 and 4.3 times higher than those of the pure ANF nanopaper, respectively. When normalized by weight, the specific tensile strength of the nanopaper is as high as 307.90 MPa·g^-1·cm³, which is even significantly superior to that of titanium alloys (257 MPa·g^-1·cm³). The ANF/CNF nanopaper also possesses excellent dielectric strength (53.42 kV mm^-1), superior UV-shielding performance (≥99.999% absorption for ultraviolet radiation), and a favorable thermostability (T_onset = 530 °C). This study proposes a new design strategy for developing ultrathin ANF-based nanopapers combined with high reliability and thermostability for application in high-end electrical insulation fields, such as 5G communication, wearable electronics, and artificial intelligence.

D-spacing controllable GO membrane intercalated by sodium tetraborate pentahydrate for dye contamination wastewater treatment

Sodium tetraborate pentahydrate (STB) was intercalated into graphene oxide (GO) nanosheets to form a nanocomposite (STB@GO). Subsequently, it was self-assembled on a substrate membrane to prepare STB@GO nanofiltration membrane. The properties of the STB@GO powder samples and the nanofiltration membrane were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), contact angle (CA), and zeta potential. When the STB concentration was 1.0 g/L in the cross-linking reaction, the membrane was described as the STB₂@GO membrane and exhibited a large interlayer space (d-spacing = 1.347 nm), high hydrophilicity (CA = 22.2°), and high negative potential (zeta = -18.0 mV). Meanwhile, the pure water flux of the membrane was significantly increased by 56.60% than that of the GO membrane. In addition, the STB₂@GO membrane exhibited a favorable capability for dye rejection,98.52% for Evans blue (EB), 99.26% for Victoria blue B (VB), 91.94% for Alizarin yellow (AY), and 93.21% for Neutral red (NR). Furthermore, the STB₂@GO membrane performed better in dye separation under various types and concentrations of dye, pH values, and ions in solution. Thus, this study provides a promising method for preparing laminated GO nanofiltration membranes for dye wastewater treatment.

Strategy to Fabricate a Strong and Supertough Bio-Inspired Fiber with Organic-Inorganic Networks in a Green and Scalable Way

Green and scalable production of some fibrous materials with higher fracture energy has long been the goal of researchers. Although some progress has been made in recent years in the research of materials with high fracture energy, inspired by the fiber structure of spider silk, it is still a great challenge to produce artificial fibers with extremely high toughness using a simple and green process. Here, we use the molecular and nanoscale engineering of calcium phosphate oligomers (CaP, < 1 nm) and waterborne polyurethanes (WPU) macromolecules that have strong interactions to form organic-inorganic networks just like β-sheet crystalline and flexible amorphous regions in spider silk. Through a simple and green route based on widespread paper string processing techniques, we fabricate a strong and supertough bioinspired fiber with a high strength (442 MPa), which is 7-15 times higher than the strength of counterpart PU (20-30 MPa), and a super toughness (640 MJ m^-3), which is 2-3.5 times higher than the toughness of spider dragline silk. This technique provides a strategy for industrially manufacturing spider fiber-like artificial fibers with a super toughness.

High-strength scalable MXene films through bridging-induced densification

[Figure: see text].

A tough, adhesive, self-healable, and antibacterial plant-inspired hydrogel based on pyrogallol-borax dynamic cross-linking

Multifunctional hydrogels that integrate stretchability, adhesion, self-healing, and antibacterial properties may find use in a variety of fields including electronic skin, wound dressings, and wearable devices; however, traditional hydrogels often exhibit short-term adhesiveness, poor mechanical properties, and a lack of antibacterial activity. Herein, a plant-inspired polyacrylamide-soybean protein isolate-pyrogallol/borax (PAM-SPI-P/B) hydrogel has been developed using a facile green method based on dynamic coordination cross-linking between pyrogallol (PG) and borax. The PG-borax dynamic bonds adjusted the network structure of the hydrogels to provide greater structural integrity to the PAM-SPI double network. This hydrogel possessed a high mechanical strength (large elongation up to 760% and compressive strength up to 1.25 MPa at 80% strain), low swelling ratio, and self-healing properties. Inspired by natural polyphenols that contain adhesive molecules, the addition of pyrogallol provided the hydrogel excellent adhesion to various hydrophilic and hydrophobic substrates. And with the inhibition of pyrogallol autoxidation due to the borax protection, the hydrogel showed repeatable and durable adhesion over 20 cycles. The obtained hydrogels also exhibited good antibacterial activities against Escherichia coli and Staphylococcus aureus because they were based on pyrogallol and borax, which have antibacterial properties. Accordingly, we envision that the PAM-SPI-P/B hydrogels have great potential for use in biomimetic tissues and biosensors.

Co-inspired hydroxyapatite-based scaffolds for vascularized bone regeneration

Hydroxyapatite (HA) is the main inorganic component of human bone. Inspired by nacre and cortical bone, hydroxyapatite-based coil scaffolds were successfully prepared. The scaffolds presented "brick and mortar" multi-layered structure of nacre and multi-layered concentric circular structure of cortical bone. Because of bioactive components and hierarchical structure, the scaffolds possessed good compressive strength (≈95 MPa), flexural strength (≈161 MPa) and toughness (≈1.1 MJ/m³). In addition, they showed improved angiogenesis and osteogenesis in rat and rabbit critical sized bone defect models. By mimicking co-biological systems, this work provided a feasible strategy to optimize the properties of traditional tissue engineering biological materials for vascularized bone regeneration.

Bioproduced Polymers Self-Assemble with Graphene Oxide into Nanocomposite Films with Enhanced Mechanical Performance

Graphene oxide (GO) has recently been highlighted as a promising multipurpose two-dimensional material. However, free-standing graphene oxide films suffer from poor strength and flexibility, which limits scaling-up of production and lifetime structural robustness in applications. Inspired by the relationship between the organic and inorganic components of the hierarchical structure of nacre found in mollusk shells, we have fabricated self-assembled, layered graphene-based composite films. The organic phase of our composite is produced via environmentally friendly and economical methods based on bacterial production of γ-poly(glutamic acid) (PGA). Composite films made of GO, PGA, and divalent cations (Ca²⁺) were prepared through a slow solvent evaporation method at ambient temperature, resulting in a nacre-like layered structure. These biobased nanocomposite films showed impressive mechanical properties, which resulted from a synergistic combination of hydrogen bonding with the bacterially produced PGA and ionic bonding with calcium ions (Ca²⁺). The GO/PGA/Ca²⁺ composite films possessed a high strength of 150 ± 51.9 MPa and a high Young's modulus of 21.4 ± 8.7 GPa, which represents an increase of 120% and over 70% with respect to pure GO films. We provide rational design strategies for the production of graphene-based films with improved mechanical performance, which can be applied in filtration purification of wastewater in the paper, food, beverage, pigment, and pharmaceuticals industries, as well as for manufacturing of functional membranes and surface coatings.

Synergistic enhancement of nanocellulose foam with dual in situ mineralization and crosslinking reaction

Cellulose nanocrystals (CNCs) foams have recently gained research interests because they are renewable, abundant, biodegradable and exhibit high surface area. However, the application of CNCs-based foams is still challenging, which is attributed to its lack of effective entanglements between the CNCs particles, thus lowering foam properties. In this study, a synergistic enhancement strategy was proposed, based on the in situ mineralization with hydroxyapatite (HAP) layer onto the CNCs surface, followed by a chemical crosslinking reaction. The physical and chemical structures of the composites were analyzed with SEM, STEM, XRD, FTIR, and TGA. By controlling the amount of coated HAP and the crosslinker, it is possible to manufacture a series of CNCs-based foams that are lightweight (50-75 mg/cm³), highly porous (~90%) with high water absorption (>1300%) and outstanding mechanical strength properties (as high as 1.37 MPa). Moreover, our study further indicated that these CNCs/HAP materials could increase the proliferation of rat osteoblast cells. The method developed in this study presents a novel approach to design improved networked CNCs foam, which has the potential to be used in thermal-retardant material, wastewater treatment, tissue engineering, and personal care applications.

Layer-by-layer assembly of bio-inspired borate/graphene oxide membranes for dye removal

Dye wastewater is harmful to the ecological environment because of its potential biological toxicity, teratogenicity, carcinogenicity, and mutagenicity. We fabricated a layered graphene oxide (GO) membrane through layer-by-layer (LBL) self-assembly. We used borate to crosslink with GO on a polyethyleneimine (PEI)-coated hydrolyzed polyacrylonitrile (hPAN) support. Fourier transform infrared (FTIR) spectrometry, Raman spectra, and x-ray photoelectron spectroscopy (XPS) confirmed the presence of a crosslinking reaction. The dynamic thermomechanical analysis (DMA) results indicated that the introduction of borate can significantly improve the mechanical properties of the membrane. The Young's modulus, ultimate tensile strength, and proportional limit of borate that was assembled twice as the outermost layer were increased by 110.81%, 62.37%, and 53.72%, respectively, as compared to those of a single-layered GO membrane. Moreover, the pure water fluxes of the layered GO membrane did not obviously decrease with an increase in the number of layers. The flux of the membrane with an outermost layer of borate was greater than that of the previous GO layer. The salt and dye rejection of the membranes was augmented with an increase in the number of layers. For the GO membrane assembled three times, rejection to methyl orange (MO), methylene blue (MB), NaCl, MgCl_2, and MgSO₄ reached 74.02%, 88.56%, 14.55%, 27.50%, and 41.95%, respectively. The use of borate as an inorganic crosslinker can avoid the environmental pollution caused by organic agents, and improve the mechanical properties as well as the filter capability of the layered GO membrane. Therefore, this study presents a novel method of membrane preparation for dye removal.

Ionic Liquid (1-Ethyl-3-methylimidazolium Acetate) Plasticization of Chitosan-Based Bionanocomposites

The structure and properties of different biopolymer composites based on chitosan and chitosan/carboxymethyl cellulose (CMC) are governed by multiple structure-property relationships associated with different phase interactions. Plasticization of these matrices with ionic liquid 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) played a dominant role, increasing the mobility of biopolymer chains as well as ions and associated dipoles but reducing biopolymer chain interactions, crystallinity, and thermal stability. These structural changes led to higher matrix ionic conductivity, shorter electrical relaxation time, and greater matrix ductility. The inclusion of graphene oxide (GO) and reduced GO (rGO) also influenced the structure and properties of these bionanocomposites by disrupting the biopolymer hydrogen bonding and/or polyelectrolyte complexation (PEC) and interacting with [C₂mim][OAc]. The impact of GO/rGO was more evident for 20 wt % [C₂mim][OAc], such as increased crystallinity and thermal stability of chitosan. PEC was hindered with excess (40 wt %) [C₂mim][OAc] added and further hindered again when rGO was included. This study shows that the structure and properties of bionanocomposites are not just determined by the surface chemistry of GO/rGO but can also be influenced by multiple interactions involving plasticizers such as ILs and additional biopolymers.

Structure and properties of thermomechanically processed chitosan/carboxymethyl cellulose/graphene oxide polyelectrolyte complexed bionanocomposites

Bionanocomposites of chitosan and chitosan/carboxymethyl cellulose (CMC) polyelectrolyte complexed materials with graphene oxide (GO) or reduced graphene oxide (rGO) were prepared by thermomechanical processing with excellent levels of dispersion. While GO has a greater affinity with the chitosan polycation, rGO had a more pronounced effect on properties resulting in increased tensile strength, Shore D hardness, and thermal stability of both matrices. Although GO is more hydrophilic than rGO, the former increased more effectively the surface hydrophobicity of the biocomposites regardless of matrix type. GO and rGO changed the α-transition of the biocomposites in a similar manner. The electrochemical properties of the biocomposites were influenced by both nanofiller type and matrix. This research revealed that inclusion of 2D carbon nanomaterials can alter biopolymer interactions and that the phase structure of the biopolymer blend may play a more important role than nanofiller-matrix interactions in determining the overall properties of these bionanocomposites.

High-Loading Boron Nitride-Based Bio-Inspired Paper with Plastic-like Ductility and Metal-like Thermal Conductivity

Although desirable in next-generation flexible electronics, fabricating hybrid film materials with excellent integration of mechanical and thermally conductive yet electrically insulating properties is still a challenge. In mollusk nacre, a small volume of the chitin nanofiber framework hosts 95 vol % CaCO₃ microplatelets, enabling the high-loading natural composites to exhibit a ductile deformation behavior. Inspired by this, we fabricate a large-area, boron nitride-based bio-inspired paper using a facile sol-gel-film conversion approach, in which BN microplatelets with a loading of 40-80 wt % are embedded into a 3D poly(p-phenylene benzobisoxazole) nanofiber framework. Because of the vital role of the 3D nanofiber framework, the BN-based paper exhibits plastic-like ductility (38-80%), ultrahigh toughness (10-100 MJ m^-3), and good folding endurance. The high-loading BN platelets form an oriented, percolative network and endow the paper with outstanding in-plane thermal conductivity (77.1-214.2 W m^-1 K^-1) comparable to that of some metals, such as aluminum alloys (108-230 W m^-1 K^-1). Using the electrically insulating BN-based paper as a flexible substrate, we demonstrate its promising application for lowering the temperature of electronic devices.

Photothermal-Responsive Graphene Oxide Membrane with Smart Gates for Water Purification

In this work, photothermal-responsive graphene oxide (GO)-based membranes intercalated by multiwalled carbon nanotubes (MWCNTs) were prepared by polydopamine (PDA) modification and 2-ureido-4[1H]-pyrimidinone (UPy) assembly process. Benefited from the high photothermal conversion ability of PDA and reversible UPy dimer, the permeation flux of the GO-based membrane can be easily modulated with a high gating ratio under near-infrared light switched off and on. Nanochannels created by the intercalation of MWCNTs into GO layers greatly increase water permeation without sacrificing the rejection of dye molecules in water (96.2% for methyl orange, 98.9% for rhodamine B, and 99.7% for Coomassie brilliant blue). The composite membranes also exhibit trade-off between rejection of heavy metal ions (Cu²⁺ and Fe³⁺). Moreover, such GO-based membranes show high pH stabilities, which show great potential in the water purification applications.

Bacterially Produced, Nacre-Inspired Composite Materials

The impressive mechanical properties of natural composites, such as nacre, arise from their multiscale hierarchical structures, which span from nano- to macroscale and lead to effective energy dissipation. While some synthetic bioinspired materials have achieved the toughness of natural nacre, current production methods are complex and typically involve toxic chemicals, extreme temperatures, and/or high pressures. Here, the exclusive use of bacteria to produce nacre-inspired layered calcium carbonate-polyglutamate composite materials that reach and exceed the toughness of natural nacre, while additionally exhibiting high extensibility and maintaining high stiffness, is introduced. The extensive diversity of bacterial metabolic abilities and the possibility of genetic engineering allows for the creation of a library of bacterially produced, cost-effective, and eco-friendly composite materials.

Bioinspired Design and Fabrication of Polymer Composite Films Consisting of a Strong and Stiff Organic Matrix and Microsized Inorganic Platelets

Intensive studies on nacre-inspired composites with exceptional mechanical properties based on an organic/inorganic hierarchical layered structure have been conducted; however, integrating high strength, stiffness, and toughness for engineering materials still remains a challenge. We herein report the design and fabrication of polymer composites through a hydrogel-film casting method that allow for building uniformly layered organic/inorganic microstructure. Alginate (Alg) was used for an organic matrix, whose mechanical properties were controlled by Ca²⁺ cross-linking toward the simultaneously strong, stiff, and tough resultant composite. Alumina (Alu) microplatelets were used for horizontally aligned inorganic phase, and their alignment and interactions with the organic matrix were improved by polyvinylpyrrolidone (PVP) coating on the platelet. The composite film exhibits well-balanced elastic and plastic deformation under tensile stress, leading to high stiffness and toughness, which have not been generally achieved in microplatelet-based composite films developed in previous studies. The synergistic effect of Ca²⁺ cross-linking and PVP-coated Alu platelets on the mechanical properties improved polymer-platelet interfacial interactions, and platelet alignment is clearly demonstrated through mechanical tests and Fourier transform infrared and X-ray diffraction analyses. We further demonstrate that the reinforcing effect of the Alu platelet and PVP-coated platelet on the mechanical properties is dependent on humidity. Such effects are maximized at highly dry conditions, which is consistent with the model estimation. Furthermore, a thick bulk composite was produced by laminating thin films and showed high mechanical properties under flexural stress. Our design and fabrication strategies combined with the understanding of their mechanism yield an alternative approach to produce engineered composite materials.

Biomimetic composite scaffold from an in situ hydroxyapatite coating on cellulose nanocrystals

A novel nanocomposite scaffold was developed by homogeneous deposition of hydroxyapatite (HAP) on a cellulose nanocrystals (CNCs) matrix suspended in a simulated body fluid (SBF). By adjusting the pH of the SBF, the HAP content in the nanocomposite could be controlled between 15 wt% and 47 wt%. Physical and chemical characteristics of the nanocomposites were analyzed by SEM, FTIR, XRD, SAED, and TEM, which confirmed the successful incorporation of HAP onto the CNCs. The nanocomposites were then freeze-casted into porous scaffolds by different solidification technologies (i.e., directional freezing (DF), plunging in liquid N₂ (PL) or in a −20 °C freezer (FZ)) followed by lyophilization. Compression testing of the HAP/CNCs foams indicated that DF caused significant improvement in mechanical properties due to the specific orientation and anisotropic porous structure compared to conventional freezing methods such as PL and FZ. Moreover, the scaffold with high HAP content exhibited improved mechanical and thermal properties, which holds potential for application in bone tissue engineering.

A novel nanocomposite scaffold was developed by homogeneous deposition of hydroxyapatite (HAP) on a cellulose nanocrystal (CNCs) matrix suspended in a simulated body fluid (SBF).

Bioinspired Macroscopic Ribbon Fibers with a Nacre-Mimetic Architecture Based on Highly Ordered Alignment of Ultralong Hydroxyapatite Nanowires

A variety of biological materials in natural organisms supply a rich source of structural design guidelines and inspirations for the construction of advanced structural materials with excellent mechanical properties. In this work, inspired by the natural nacre and human bone, a kind of flexible macroscopic ribbon fiber made from highly ordered alignment of ultralong hydroxyapatite (HAP) nanowires and sodium polyacrylate (PAAS) with a "brick-and-mortar" layered structure has been developed by a scalable and convenient wet-spinning method. The quasi-long-range orderly liquid crystal of one-dimensional ultralong hydroxyapatite nanowires is employed and spun into the continuous flexible macroscopic ribbon fiber. In this work, highly ordered ultralong HAP nanowires act as the hard "brick" and PAAS acts as the soft "mortar", and the nacre-mimetic layered architecture is obtained. The as-prepared flexible macroscopic HAP/PAAS ribbon fiber exhibits superior mechanical properties, and the maximum tensile strength and Young's modulus are as high as 203.58 ± 45.38 MPa and 24.56 ± 5.35 GPa, respectively. In addition, benefiting from the excellent flexibility and good knittability, the as-prepared macroscopic HAP/PAAS ribbon fiber can be woven into various flexible macroscopic architectures. Additionally, the as-prepared flexible macroscopic HAP/PAAS ribbon fiber can be further functionalized by incorporation of various functional components, such as magnetic and photoluminescent constituents. The as-prepared flexible macroscopic HAP/PAAS ribbon fiber has potential applications in various fields such as smart wearable devices, optical devices, magnetic devices, and biomedical engineering.

Bioinspired reinforcement of cyclosiloxane hybrid polymer

Structural analysis showed that cyclosiloxane hybrid polymer (CHP) is a collection of nano-sized nacre-like structures in random orientations. Inspired by the reinforcement of nacre-like materials, basal-functionalized graphene (GO-AA) was inserted between CHP layers, acting as 'double-sided tape' to improve the mechanical properties. The resulting GO-AA/CHP nanocomposites showed a 156% improvement in toughness with only a 0.08 wt% loading of GO-AA, and a 25% improvement in thermal conductivity with a 0.10 wt% loading of GO-AA. The proposed 'double-sided tape' effect was also used to explain the highly efficient enhancement in thermal conductivity. This research promotes the application of CHP in harsher environments, demonstrates its prospects in thermal management areas, and contributes to nature-inspired materials design.

Strong, Conductive, Foldable Graphene Sheets by Sequential Ionic and π Bridging

The goal of this work is to develop an inexpensive low-temperature process that provides polymer-free, high-strength, high-toughness, electrically conducting sheets of reduced graphene oxide (rGO). To develop this process, we have evaluated the mechanical and electrical properties resulting from the application of an ionic bonding agent (Cr3+ ), a π-π bonding agent comprising pyrene end groups, and their combinations for enhancing the performance of rGO sheets. When only one bonding agent was used, the π-π bonding agent is much more effective than the ionic bonding agent for improving both the mechanical and electrical properties of rGO sheets. However, the successive application of ionic bonding and π-π bonding agents maximizes tensile strength, toughness, long-term electrical stability in various corrosive solutions, and resistance to mechanical abuse and ultrasonic dissolution. Using a combination of ionic bonding and π-π bonding agents, high tensile strength (821 MPa), high toughness (20 MJ m-3 ), and electrical conductivity (416 S cm-1 ) were obtained, as well as remarkable retention of mechanical and electrical properties during ultrasonication and mechanical cycling by both sheet stretch and sheet folding, suggesting high potential for applications in aerospace and flexible electronics.

Facile and On-Demand Cross-Linking of Nacre-Mimetic Nanocomposites Using Tailor-Made Polymers with Latent Reactivity

The development of on-demand cross-linking strategies is a key aspect in promoting mechanical properties of high-performance bioinspired nanocomposites. Here, we embed styrene sulfonyl azide groups with latent chemical reactivity into water-soluble copolymers and assemble those with high-aspect-ratio synthetic nanoclays to generate well-defined layered polymer/nanoclay nacre-mimetics. A considerable stiffening and strengthening occurs upon activation of the covalent cross-linking using simple heating. Varying the amount of cross-linkable units allows molecular control of mechanical properties from ductile to stiff and strong. Moreover, the covalent cross-linking enhances the moisture stability of water-borne nacre-mimetics. The strategy is facile and versatile allowing for a transfer into applications.

High-strength and morphology-controlled aerogel based on carboxymethyl cellulose and graphene oxide

Composite aerogels with excellent mechanical properties were prepared by using carboxymethyl cellulose (CMC) as raw materials, 2D graphene oxide (GO) nanosheets as reinforcement, boric acid (BA) as cross-linker. By controlling the heat transfer rate, composite aerogels with isotropy and anisotropy structure were prepared, the mechanical and heat insulation properties were studied. The isotropy composite aerogel had compression strength of 110 kPa at 60% compression, which was 5 times of the axial and 14 times of the radial of anisotropy structure composite aerogels, and thermal conductivity was also lower than those of two directions of anisotropy composite aerogel. Besides, the mechanical properties of isotropy composite aerogels increased with the increase of GO content. When GO content was up to 5 wt%, the compressive strength and Young's modulus of composite aerogels reached 349 kPa and 1029 kPa, which were 1.6 and 4.5 times that of CMC aerogels, respectively.

Biomimetic Domain-Active Electrospun Scaffolds Facilitating Bone Regeneration Synergistically with Antibacterial Efficacy for Bone Defects

To improve bone regeneration in oral microenvironment, we generated a novel biodegradable, antibacterial, and osteoconductive electrospun PLGA/PCL membrane as an ideal osteogenic scaffold. The novel three-layer membranes were structured with serial layers of electrospun chlorhexidine-doped-PLGA/PCL (PPC), PLGA/PCL (PP), and β-tricalcium phosphate-doped-PLGA/PCL (PPβ). To characterize osteoconductive properties of these membranes, MC3T3-E1 (MC) cultures were seeded onto the membranes for 14 days for evaluation of cell proliferation, morphology and gene/protein expression. In addition, MC cells were cultured onto different surfaces of the three-layer membranes, PPC layer facing MC cells (PPβ-PP-PPC) and PPβ layer facing MC cells (PPC-PP-PPβ) to evaluate surface-material effects. Membrane properties and structures were evaluated. Antibacterial properties against Streptococcus mutans and Staphylococcus aureus were determined. Scanning electron microscope demonstrated smaller interfiber spaces of PPC and PPβ-PP-PPC compared to PPβ, PPC-PP-PPβ, and PP. PPC and PPβ-PP-PPC exhibited hydrophilic property. The three-layer membranes (PPC-PP-PPβ and PPβ-PP-PPC) demonstrated significantly higher Young's modulus (94.99 ± 4.03 MPa and 92.88 ± 4.03 MPa) compared to PP (48.76 ± 18.15 MPa) or PPC (7.92 ± 3.97 MPa) (p < 0.05). No significant difference of cell proliferation was found among any groups at any time point (p > 0.05). Higher expression of integrins were detected at 12 h of cultures on PPC-PP-PPβ compared to the controls. Promoted osteoconductive effects of PPC-PP-PPβ were revealed by alkaline phosphatase assays and Western blot compared with the controls at 7 and 14 days. PPC, PPC-PP-PPβ and PPβ-PP-PPC exhibited a significantly wider antibacterial zone against the tested bacteria compared to PP and PPβ (p < 0.05). These results suggested that the three-layer electrospun membranes demonstrated superior properties: higher strength, better cell adhesion, and promoted osteoconductive properties compared to single-layer membrane: however, antibacterial properties were exhibited in three-layer electrospun membranes and chlorhexidine-doped single-layer membrane. We concluded that the novel three-layer membranes could be used as a biocompatible scaffold for intraoral bone regeneration due to its enhanced osteoconductive activity and antibacterial effect.

Fabrication of Water-Resistant Nacre-like Polymer/Clay Nanocomposites via in Situ Polymerization

Fabrication and characterization of water-resistant nacre-like polymer/clay nanocomposites, in which clay platelets and hydrophobic polymer chains are alternately stacked in parallel, are reported. Hydrophilic clay was converted by an ion-exchange reaction with a methacrylate monomer having a long alkyl chain and a quaternary ammonium salt group at the end. The subsequent in situ polymerization bound the neighboring clay surfaces, leading to the preferential orientation of the clay platelets owing to their high aspect ratio. The composites maintained excellent mechanical properties even after being immersed in water for more than a day. Strong shape stability was observed in water as well as in various organic solvents.

Topological Design of Ultrastrong and Highly Conductive Graphene Films

Nacre-like graphene films are prepared by evaporation-induced assembly of graphene oxide dispersions containing small amounts of cellulose nanocrystal (CNC), followed by chemical reduction with hydroiodic acid. CNC induces the formation of wrinkles on graphene sheets, greatly enhancing the mechanical properties of the resultant graphene films. The graphene films deliver an ultrahigh tensile strength of 765 ± 43 MPa (up to 800 MPa in some cases), a large failure strain of 6.22 ± 0.19%, and a superior toughness of 15.64 ± 2.20 MJ m^-3 , as well as a high electrical conductivity of 1105 ± 17 S cm^-1 . They have a great potential for applications in flexible electronics because of their combined excellent mechanical and electrical properties.

Reduced Graphene Oxide/Alumina, A Good Accelerant for Cellulose-Based Artificial Nacre with Excellent Mechanical, Barrier, and Conductive Properties

In this article, a simple strategy was employed to fabricate bioinspired hybrid composite with carboxymethyl cellulose (CMC), graphene oxide, and reduced graphene oxide/alumina (rGO/Al) by a facile solution casting method. The tensile strength and toughness of rGO/Al-CMC-GO can reach 586.6 ± 12 MPa, 12.1 ± 0.44 MJm^-3, respectively, due to the interface strengthening of alumina, which is 1.43 and 12 times higher than steel and about 4.3 and 6.7 times that of nature nacre. The artificial nacre hybrid composite is conductive due to the introduction of rGO/Al on the surface. Interestingly this structure can also be coated on the surface of cotton thread to give the thread good mechanical performance and conductivity. Additionally, the artificial nacre has better fire shielding and gas barrier properties. The oxygen permeability (OP) for 1% rGO/Al-CMC decreased from 0.0265 to 0.003 mLμm m^-2 day^-1 kpa^-1, the water vapor permeability (WVP) decreased from 0.363 to 0.205 gmmm^-2 day^-1 kpa^-1 when the concentration increased from 1% rGO/Al to 6% rGO/Al. It is believed this work provided a simple and feasible strategy to fabricate ultrastrong and ultratough graphene-based artificial nacre multifunctional materials.

Ultrastrong and Bioactive Nanostructured Bio-Based Composites

Nature's design of functional materials relies on smart combinations of simple components to achieve desired properties. Silk and cellulose are two clever examples from nature-spider silk being tough due to high extensibility, whereas cellulose possesses unparalleled strength and stiffness among natural materials. Unfortunately, silk proteins cannot be obtained in large quantities from spiders, and recombinant production processes are so far rather expensive. We have therefore combined small amounts of functionalized recombinant spider silk proteins with the most abundant structural component on Earth (cellulose nanofibrils (CNFs)) to fabricate isotropic as well as anisotropic hierarchical structures. Our approach for the fabrication of bio-based anisotropic fibers results in previously unreached but highly desirable mechanical performance with a stiffness of ∼55 GPa, strength at break of ∼1015 MPa, and toughness of ∼55 MJ m^-3. We also show that addition of small amounts of silk fusion proteins to CNF results in materials with advanced biofunctionalities, which cannot be anticipated for the wood-based CNF alone. These findings suggest that bio-based materials provide abundant opportunities to design composites with high strength and functionalities and bring down our dependence on fossil-based resources.