Hierarchical and reconfigurable interfibrous interface of bioinspired Bouligand structure enabled by moderate orderliness.

Introducing natural Bouligand structure into synthetics is expected to develop high-performance structural materials. Interfibrous interface is critical to load transfer, and mechanical functionality of bioinspired Bouligand structure yet receives little attention. Here, we propose one kind of hierarchical and reconfigurable interfibrous interface based on moderate orderliness to mechanically reinforce bioinspired Bouligand structure. The interface imparted by moderate alignment of adaptable networked nanofibers hierarchically includes nanofiber interlocking and hydrogen-bonding (HB) network bridging, being expected to facilitate load transfer and structural stability through dynamic adjustment in terms of nanofiber sliding and HB breaking-reforming. As one demonstration, the hierarchical and reconfigurable interfibrous interface is constructed based on moderate alignment of networked bacterial cellulose nanofibers. We show that the resultant bioinspired Bouligand structural material exhibits unusual strengthening and toughening mechanisms dominated by interface-microstructure multiscale coupling. The proposed interfibrous interface enabled by moderate orderliness would provide mechanical insight into the assembly of widely existing networked nanofiber building blocks toward high-performance macroscopic bioinspired structural assemblies.

Bottom-Up Film-to-Bulk Assembly Toward Bioinspired Bulk Structural Nanocomposites.

Biological materials, although composed of meager minerals and biopolymers, often exhibit amazing mechanical properties far beyond their components due to hierarchically ordered structures. Understanding their structure-properties relationships and replicating them into artificial materials would boost the development of bulk structural nanocomposites. Layered microstructure widely exists in biological materials, serving as the fundamental structure in nanosheet-based nacres and nanofiber-based Bouligand tissues, and implying superior mechanical properties. High-efficient and scalable fabrication of bioinspired bulk structural nanocomposites with precise layered microstructure is therefore important yet remains difficult. Here, one straightforward bottom-up film-to-bulk assembly strategy is focused for fabricating bioinspired layered bulk structural nanocomposites. The bottom-up assembly strategy inherently offers a methodology for precise construction of bioinspired layered microstructure in bulk form, availability for fabrication of bioinspired bulk structural nanocomposites with large sizes and complex shapes, possibility for design of multiscale interfaces, feasibility for manipulation of diverse heterogeneities. Not limited to discussing what has been achieved by using the current bottom-up film-to-bulk assembly strategy, it is also envisioned how to promote such an assembly strategy to better benefit the development of bioinspired bulk structural nanocomposites. Compared to other assembly strategies, the highlighted strategy provides great opportunities for creating bioinspired bulk structural nanocomposites on demand.

Bioinspired polysaccharide-based nanocomposite membranes with robust wet mechanical properties for guided bone regeneration.

Polysaccharide-based membranes with excellent mechanical properties are highly desired. However, severe mechanical deterioration under wet conditions limits their biomedical applications. Here, inspired by the structural heterogeneity of strong yet hydrated biological materials, we propose a strategy based on heterogeneous crosslink-and-hydration (HCH) of a molecule/nano dual-scale network to fabricate polysaccharide-based nanocomposites with robust wet mechanical properties. The heterogeneity lies in that the crosslink-and-hydration occurs in the molecule-network while the stress-bearing nanofiber-network remains unaffected. As one demonstration, a membrane assembled by bacterial cellulose nanofiber-network and Ca2+-crosslinked and hydrated sodium alginate molecule-network is designed. Studies show that the crosslinked-and-hydrated molecule-network restricts water invasion and boosts stress transfer of the nanofiber-network by serving as interfibrous bridge. Overall, the molecule-network makes the membrane hydrated and flexible; the nanofiber-network as stress-bearing component provides strength and toughness. The HCH dual-scale network featuring a cooperative effect stimulates the design of advanced biomaterials applied under wet conditions such as guided bone regeneration membranes.

Sr-induced Fermi Engineering of ß-FeOOH for Multifunctional Catalysis.

Designing a multifunctional electrocatalyst to produce H2 from water, urea, urine, and wastewater, is highly desirable yet challenging because it demands precise Fermi-engineering to realize stronger π-donation from O 2p to electron(e- )-deficient metal (t2g ) d-orbitals. Here a Sr-induced phase transformed ß-FeOOH/α-Ni(OH)2 catalyst anchored on Ni-foam (designated as pt-NFS) is introduced, where Sr produces plenteous Fe4+ (Fe3+ → Fe4+ ) to modulate Fermi level and e- -transfer from e- -rich Ni3+ (t2g )-orbitals to e- -deficient Fe4+ (t2g )-orbitals, via strong π-donation from the π-symmetry lone-pair of O bridge. pt-NFS utilizes Fe-sites near the Sr-atom to break the H─O─H bonds and weakens the adsorption of *O while strengthening that of *OOH, toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Invaluably, Fe-sites of pt-NFS activate H2 -production from urea oxidation reaction (UOR) through a one-stage pathway which, unlike conventional two-stage pathways with two NH3 -molecules, involves only one NH3 -molecule. Owing to more suitable kinetic energetics, pt-NFS requires 133 mV (negative potential shift), 193 mV, ≈1.352 V, and ≈1.375 V versus RHE for HER, OER, UOR, and human urine oxidation, respectively, to reach the benchmark 10 mA cm-2 and also demonstrates remarkable durability of over 25 h. This work opens a new corridor to design multifunctional electrocatalysts with precise Fermi engineering through d-band modulation.

Electron-Sponge Nature of Polyoxometalates for Next-Generation Electrocatalytic Water Splitting and Nonvolatile Neuromorphic Devices.

Designing next-generation molecular devices typically necessitates plentiful oxygen-bearing sites to facilitate multiple-electron transfers. However, the theoretical limits of existing materials for energy conversion and information storage devices make it inevitable to hunt for new competitors. Polyoxometalates (POMs), a unique class of metal-oxide clusters, have been investigated exponentially due to their structural diversity and tunable redox properties. POMs behave as electron-sponges owing to their intrinsic ability of reversible uptake-release of multiple electrons. In this review, numerous POM-frameworks together with desired features of a contender material and inherited properties of POMs are systematically discussed to demonstrate how and why the electron-sponge-like nature of POMs is beneficial to design next-generation water oxidation/reduction electrocatalysts, and neuromorphic nonvolatile resistance-switching random-access memory devices. The aim is to converge the attention of scientists who are working separately on electrocatalysts and memory devices, on a point that, although the application types are different, they all hunt for a material that could exhibit electron-sponge-like feature to realize boosted performances and thus, encouraging the scientists of two completely different fields to explore POMs as imperious contenders to design next-generation nanodevices. Finally, challenges and promising prospects in this research field are also highlighted.

Designing nanohesives for rapid, universal, and robust hydrogel adhesion.

Nanoparticles-based glues have recently been shown with substantial potential for hydrogel adhesion. Nevertheless, the transformative advance in hydrogel-based application places great challenges on the rapidity, robustness, and universality of achieving hydrogel adhesion, which are rarely accommodated by existing nanoparticles-based glues. Herein, we design a type of nanohesives based on the modulation of hydrogel mechanics and the surface chemical activation of nanoparticles. The nanohesives can form robust hydrogel adhesion in seconds, to the surface of arbitrary engineering solids and biological tissues without any surface pre-treatments. A representative application of hydrogel machine demonstrates the tough and compliant adhesion between dynamic tissues and sensors via nanohesives, guaranteeing accurate and stable blood flow monitoring in vivo. Combined with their biocompatibility and inherent antimicrobial properties, the nanohesives provide a promising strategy in the field of hydrogel based engineering.

Biomimetic Gradient Bouligand Structure Enhances Impact Resistance of Ceramic-Polymer Composites.

Biological materials relied on multiple synergistic structural design elements typically exhibit excellent comprehensive mechanical properties. Hierarchical incorporation of different biostructural elements into a single artificial material is a promising approach to enhance mechanical properties, but remains challenging. Herein, a biomimetic structural design strategy is proposed by coupling gradient structure with twisted plywood Bouligand structure, attempting to improve the impact resistance of ceramic-polymer composites. Via robocasting and sintering, kaolin ceramic filaments reinforced by coaxially aligned alumina nanoplatelets are arranged into Bouligand structure with a gradual transition in filament spacing along the thickness direction. After the following polymer infiltration, biomimetic ceramic-polymer composites with a gradient Bouligand (GB) structure are eventually fabricated. Experimental investigations reveal that the incorporation of gradient structure into Bouligand structure improves both the peak force and total energy absorption of the obtained ceramic-polymer composites. Computational modeling further suggests the substantial improvement in impact resistance by adopting GB structure, and clarifies the underlying deformation behavior of the biomimetic GB structured composites under impact. This biomimetic design strategy may provide valuable insights for developing lightweight and impact-resistant structural materials in the future.

Mechanically robust bamboo node and its hierarchically fibrous structural design.

Although short bamboo nodes function in mechanical support and fluid exchange for bamboo survival, their structures are not fully understood compared to unidirectional fibrous internodes. Here, we identify the spatial heterostructure of the bamboo node via multiscale imaging strategies and investigate its mechanical properties by multimodal mechanical tests. We find three kinds of hierarchical fiber reinforcement schemes that originate from the bamboo node, including spatially tightened interlocking, triaxial interconnected scaffolding and isotropic intertwining. These reinforcement schemes, built on porous vascular bundles, microfibers and more-refined twist-aligned nanofibers, govern the structural stability of the bamboo via hierarchical toughening. In addition, the spatial liquid transport associated with these multiscale fibers within the bamboo node is experimentally verified, which gives perceptible evidence for life-indispensable multidirectional fluid exchange. The functional integration of mechanical reinforcement and liquid transport reflects the fact that the bamboo node has opted for elaborate structural optimization rather than ingredient richness. This study will advance our understanding of biological materials and provide insight into the design of fiber-reinforced structures and biomass utilization.

Scalable Manufacturing of Mechanical Robust Bioinspired Ceramic-Resin Composites with Locally Tunable Heterogeneous Structures.

Lightweight structural materials with a unique combination of high stiffness, strength, toughness, and hardness, are highly desired yet challenging to be artificially fabricated. Biological structural materials, on the other hand, ingeniously integrate multiple mutually exclusive mechanical properties together relying on their hierarchically heterogeneous structures bonded with gradient interfaces. Here, a scalable bottom-up approach combining continuous nanofiber-assisted evaporation-induced self-assembly with laminating, pressure-less sintering and resin infiltration is reported to fabricate bioinspired heterogeneous ceramic-resin composites with locally tunable microstructure to fulfill specific properties. A gradient interlayer is introduced to provide a gradual transition between adjacent heterogeneous layers, effectively alleviating their property mismatch. The optimized heterogeneous nacre-like composite, as a demonstration, exhibits an attractive combination of low density (≈2.8 g cm-3 ), high strength (≈292 MPa), toughness (≈6.4 MPa m1/2 ), surface hardness (≈1144 kgf mm-2 ) and impact-resistance, surpassing the overall performance of engineering alumina. This material-independent approach paves the way for designing advanced bioinspired heterogeneous materials for diverse structural and functional applications.

Bioinspired Impact-Resistant and Self-Monitoring Nanofibrous Composites.

Lightweight and impact-resistant materials with self-monitoring capability are highly desired for protective applications, but are challenging to be artificially fabricated. Herein, a scalable-manufactured aramid nanofiber (ANF)-based composite combining these key properties is presented. Inspired by the strengthening and toughening mechanisms relying on recoverable interfaces commonly existing in biological composites, mechanically weak but dense hydrogen bonds are introduced into the ANF interfaces to achieve simultaneously enhanced tensile strength (300 MPa), toughness (55 MJ m-3 ), and impact resistance of the nanofibrous composite. The achieved mechanical property combination displays attractive advantages compared with that of most of previously reported nanocomposites. Additionally, the nanofibrous composite is designed with a capability for real-time self-monitoring of its structural safety during both quasi-static tensile and dynamic impact processes, based on the strain/damage-induced resistance variations of a conductive nanowire network inside it. These comprehensive properties enable the present nanofibrous composite with promising potential for protective applications.

Controlled Desiccation of Preprinted Hydrogel Scaffolds Toward Complex 3D Microarchitectures.

Additive manufacturing (AM) is the key to creating a wide variety of 3D structures with unique and programmable functionalities. Direct ink writing is one of the widely used AM technologies with numerous printable materials. However, the extrude-based method is limited by low fabrication resolution, which is confined to printing macrostructures. Herein, a new AM strategy is reported, using a low-cost extrusion 3D printer, to create 3D microarchitectures at the macroscopic level through controlled desiccation of preprinted hydrogel scaffolds followed by infilling objective components. A printable hydrogel with a high-water content ensures maximum shrinkage (≈99.5% in volume) of the printed scaffolds to achieve high resolution. Stable covalent cross-linking and a suitable drying rate enable uniform shrinkage of the scaffolds to retain their original architectures. Particularly, this method can be adapted to produce liquid-metal-based 3D circuits and nanocomposite-based microrobots, indicating its capability to fabricate functional and complex 3D architectures with micron-level resolution from different material systems.

Large-Scale Production of Rectorite Nanosheets and Their Co-Assembly with Aramid Nanofibers for High-Performance Electrical Insulating Nanopapers.

Compared with raw rectorite microplatelets (RMs), rectorite nanosheets (RNs) have considerably greater application prospects in the preparation of advanced composite materials because of their larger aspect ratio, higher surface reactivity, and intrinsically superior mechanical and physical properties. However, the difficulty in the efficient preparation of RNs significantly limits their large-scale applications. Here, a scalable poly(vinylpyrrolidone)-assisted stirring approach is developed to prepare ultrathin RNs from the abundant natural RMs. A higher production rate (≈0.675 g h-1 ) is achieved compared with that of most other nanosheets. Additionally, instead of using conventional time- and energy-consuming high-speed centrifugation, an efficient poly(dienedimethylammonium chloride)-assisted sedimentation strategy is proposed here to rapidly separate the exfoliated RNs from the RN dispersion. Then, the RNs are co-assembled with aramid nanofibers (ANFs) into large-scale nacre-mimetic ANF-RN nanopapers with considerably enhanced mechanical, electrical insulating, and high-temperature-resistant properties compared with pure ANF nanopapers and ANF-RM micropapers. Moreover, these properties are superior to those of previously reported ANF-based nanopapers and commercial insulating micropapers.

Highly hydrated paramagnetic amorphous calcium carbonate nanoclusters as an MRI contrast agent.

Amorphous calcium carbonate plays a key role as transient precursor in the early stages of biogenic calcium carbonate formation in nature. However, due to its instability in aqueous solution, there is still rare success to utilize amorphous calcium carbonate in biomedicine. Here, we report the mutual effect between paramagnetic gadolinium ions and amorphous calcium carbonate, resulting in ultrafine paramagnetic amorphous carbonate nanoclusters in the presence of both gadolinium occluded highly hydrated carbonate-like environment and poly(acrylic acid). Gadolinium is confirmed to enhance the water content in amorphous calcium carbonate, and the high water content of amorphous carbonate nanoclusters contributes to the much enhanced magnetic resonance imaging contrast efficiency compared with commercially available gadolinium-based contrast agents. Furthermore, the enhanced T1 weighted magnetic resonance imaging performance and biocompatibility of amorphous carbonate nanoclusters are further evaluated in various animals including rat, rabbit and beagle dog, in combination with promising safety in vivo. Overall, exceptionally facile mass-productive amorphous carbonate nanoclusters exhibit superb imaging performance and impressive stability, which provides a promising strategy to design magnetic resonance contrast agent.

Anti-Swelling, Robust, and Adhesive Extracellular Matrix-Mimicking Hydrogel Used as Intraoral Dressing.

Due to the wet and dynamic environment of the oral cavity, the healing of intraoral wounds, such as tooth extraction wounds, requires stable and firm wound dressings. In clinical practice, cotton balls and gauzes, sponge plugs, or sutures are used to treat extraction wounds, but none of these means can continuously isolate the wound from the intraoral environment and facilitate ideal healing conditions. Herein, inspired by the natural extracellular matrix, a family of wound dressings is developed for intraoral wound repair. Infiltrating a ductile long-chain hydrogel network into a prefabricated, sturdy macromolecular meshwork and in situ crosslinking endowed the composite hydrogel with controllable swelling behaviors and robust mechanical properties. The macromolecular meshwork functioned as the backbone to support the composite and restricts the swelling of the long-chain hydrogel network. In vitro tests verified that this wound dressing can provide durable protection for intraoral wounds against complex irritations. Furthermore, accelerated wound healing occurred when the wound dressing is applied in vivo on a canine tooth extraction model, due to the effective reduction of acute inflammation. These results suggest that this family of bioinspired hydrogels has great potential for application as intraoral wound dressing.

Double-Layer Nacre-Inspired Polyimide-Mica Nanocomposite Films with Excellent Mechanical Stability for LEO Environmental Conditions.

Owing to their outstanding comprehensive performance, polyimide (PI) composite films are widely used on the external surfaces of spacecraft to protect them from the adverse conditions of low Earth orbit (LEO). However, current PI composite films have inadequate mechanical properties and atomic oxygen (AO) resistance. Herein, this work fabricates a new PI-based nanocomposite film with greatly enhanced mechanical properties and AO resistance by integrating mica nanosheets with PI into a unique double-layer nacre-inspired structure with a much higher density of mica nanosheets in the top layer. In addition, the unique microstructure and the intrinsic properties of mica also impart the nanocomposite film with favorable ultraviolet and high-temperature resistance. The comprehensive performance of this material is superior to those of pure PI, single-layer PI-mica, and previously reported PI-based composite films. Thus, the double-layer nanocomposite film displays great potential as an aerospace material for use in LEO.

A Highly Compressible and Stretchable Carbon Spring for Smart Vibration and Magnetism Sensors.

Porous carbon materials demonstrate extensive applications for their attractive characteristics. Mechanical flexibility is an essential property guaranteeing their durability. After decades of research efforts, compressive brittleness of porous carbon materials is well resolved. However, reversible stretchability remains challenging to achieve due to the intrinsically weak connections and fragile joints of the porous carbon networks. Herein, it is presented that a porous all-carbon material achieving both elastic compressibility and stretchability at large strain from -80% to 80% can be obtained when a unique long-range lamellar multi-arch microstructure is introduced. Impressively, the porous all-carbon material can maintain reliable structural robustness and durability under loading condition of cyclic compressing-stretching process, similar to a real metallic spring. The unique performance renders it as a promising platform for making smart vibration and magnetism sensors, even capable of operating at extreme temperatures. Furthermore, this study provides valuable insights for creating highly stretchable and compressible porous materials from other neat inorganic components for diverse applications in future.

Nacreous aramid-mica bulk materials with excellent mechanical properties and environmental stability.

Low density, high strength and toughness, together with good environmental stability are always desirable but hardly to achieve simultaneously for man-made structural materials. Replicating the design motifs of natural nacre clearly provides one promising route to obtain such kind of materials, but fundamental challenges remain. Herein, by choosing aramid nanofibers and mica microplatelets as building blocks, we produce a nacreous aramid-mica bulk material with a favorable combination of low density (∼1.7 g cm-3), high strength (∼387 MPa) and toughness (∼14.3 MPa m1/2), and impressive mechanical stability in some harsh environments, including acid/alkali solutions, strong ultraviolet radiation, boiling water, and liquid nitrogen, standing out from previously reported biomimetic bulk composites. Moreover, the obtained material outperforms other bulk nacre-mimetics and most engineering structural materials in terms of its specific strength (227 MPa/[Mg m-3]) and specific toughness (8.4 MPa m1/2/[Mg m-3]), making it a new promising engineering structural material for different technical fields.

Bioinspired hierarchical helical nanocomposite macrofibers based on bacterial cellulose nanofibers.

Bio-sourced nanocellulosic materials are promising candidates for spinning high-performance sustainable macrofibers for advanced applications. Various strategies have been pursued to gain nanocellulose-based macrofibers with improved strength. However, nearly all of them have been achieved at the expense of their elongation and toughness. Inspired by the widely existed hierarchical helical and nanocomposite structural features in biosynthesized fibers exhibiting exceptional combinations of strength and toughness, we report a design strategy to make nanocellulose-based macrofibers with similar characteristics. By combining a facile wet-spinning process with a subsequent multiple wet-twisting procedure, we successfully obtain biomimetic hierarchical helical nanocomposite macrofibers based on bacterial cellulose nanofibers, realizing impressive improvement in their tensile strength, elongation and toughness simultaneously. The achievement certifies the validity of the bioinspired hierarchical helical and nanocomposite structural design proposed here. This bioinspired design strategy provides a potential platform for further optimizing or creating many more strong and tough nanocomposite fiber materials for diverse applications.

Temperature-Invariant Superelastic and Fatigue Resistant Carbon Nanofiber Aerogels.

Superelastic and fatigue-resistant materials that can work over a wide temperature range are highly desired for diverse applications. A morphology-retained and scalable carbonization method is reported to thermally convert a structural biological material (i.e., bacterial cellulose) into graphitic carbon nanofiber aerogel by engineering the pyrolysis chemistry. The prepared carbon aerogel perfectly inherits the hierarchical structures of bacterial cellulose from macroscopic to microscopic scales, resulting in remarkable thermomechanical properties. In particular, it maintains superelasticity without plastic deformation even after 2 × 106 compressive cycles and exhibits exceptional temperature-invariant superelasticity and fatigue resistance over a wide temperature range at least from -100 to 500 °C. This aerogel shows unique advantages over polymeric foams, metallic foams, and ceramic foams in terms of thermomechanical stability and fatigue resistance, with the realization of scalable synthesis and the economic advantage of biological materials.

Bioinspired Unidirectional Silk Fibroin-Silver Compound Nanowire Composite Scaffold via Interface-Mediated In Situ Synthesis.

Bioinspired unidirectional porous materials have emerged as a unique class of scaffolds for the fabrication of macroscopic nanomaterial assemblies. However, these scaffolds usually serve simply as mechanical carriers to support various building blocks. Here, we report that the unidirectional silk fibroin scaffold can not only act as a carrier, but also serve as a controllable multiscale reactor to achieve the in situ synthesis of a Ag3 PO4 nanowire network anchored to ordered channels. Both the silk fibroin matrix and the interface play important roles in the nucleation and growth of the Ag3 PO4 nanowires. This unidirectional composite scaffold can be used for efficient water disinfection. Furthermore, the facile chemical transformation of Ag3 PO4 in the composite scaffold into Ag2 S provided an analogous unidirectional composite silk scaffold that displays both efficient solar water evaporation effect and antibacterial activity. It is expected that this method can be extended to fabricate a series of silk-based unidirectional composite scaffolds with varying functionalities.