Bio-inspired copper ion-chelated chitosan coating modified UHMWPE fibers for enhanced interfacial properties of composites.

Ultra-high molecular weight polyethylene (UHMWPE) fibers are broadly applied in lightweight and high-strength composite fiber materials. However, the development of UHMWPE fibers is limited by their smooth and chemically inert surfaces. To address the issues, a modified UHMWPE fibers material has been fabricated through the chelation reaction between Cu2+ and chitosan coatings within the surface of fibers after plasma treatment, which is inspired by the hardening mechanism, a crosslinked network between metal ions and proteins/polysaccharides of the tips and edges in arthropod-specific cuticular tools. The coatings improve the surface wettability and interfacial bonding ability, which are beneficial in extending the application range of UHMWPE fibers. More importantly, compared to the unmodified UHMWPE fiber cloths, the tensile property of the modified fiber cloths is increased by 18.89% without damaging the strength, which is infrequent in modified UHMWPE fibers. Furthermore, the interlaminar shear strength and fracture toughness of the modified fibers laminate are increased by 37.72% and 135.90%, respectively. These improvements can be attributed to the synergistic effects between the surface activity and the tiny bumps of the modified UHMWPE fibers. Hence, this work provides a more straightforward and less damaging idea of fiber modification for manufacturing desirable protective and medical materials.

Bacteria engineered with intracellular and extracellular nanomaterials for hierarchical modulation of antitumor immune responses.

Induction of immunogenic cell death (ICD) by hyperthermia can initiate adaptive immune responses, emerging as an attractive strategy for tumor immunotherapy. However, ICD can induce proinflammatory factor interferon-γ (IFN-γ) production, leading to indoleamine 2,3-dioxygenase 1 (IDO-1) activation and an immunosuppressive tumor microenvironment, which dramatically reduces the ICD-triggered immunotherapeutic efficacy. Herein, we developed a bacteria-nanomaterial hybrid system (CuSVNP20009NB) to systematically modulate the tumor immune microenvironment and improve tumor immunotherapy. Attenuated Salmonella typhimurium (VNP20009) that can chemotactically migrate to the hypoxic area of the tumor and repolarize tumor-associated macrophages (TAMs) was employed to intracellularly biosynthesize copper sulfide nanomaterials (CuS NMs) and extracellularly hitchhike NLG919-embedded and glutathione (GSH)-responsive albumin nanoparticles (NB NPs), forming CuSVNP20009NB. After intravenous injection into B16F1 tumor-bearing mice, CuSVNP20009NB could accumulate in tumor tissues and repolarize TAMs from the immunosuppressive M2 to immunostimulatory M1 phenotype and release NLG919 from extracellular NB NPs to inhibit IDO-1 activity. Under further near infrared laser irradiation, intracellular CuS NMs of CuSVNP20009NB could photothermally induce ICD including calreticulin (CRT) expression and high mobility group box 1 (HMGB-1) release, promoting intratumoral infiltration of cytotoxic T lymphocytes. Finally, CuSVNP20009NB with excellent biocompatibility could systematically augment immune responses and significantly inhibit tumor growth, holding great promise for tumor therapy.

Lightweight Structural Biomaterials with Excellent Mechanical Performance: A Review.

The rational design of desirable lightweight structural materials usually needs to meet the strict requirements of mechanical properties. Seeking optimal integration strategies for lightweight structures and high mechanical performance is always of great research significance in the rapidly developing composites field, which also draws significant attention from materials scientists and engineers. However, the intrinsic incompatibility of low mass and high strength is still an open challenge for achieving satisfied engineering composites. Fortunately, creatures in nature tend to possess excellent lightweight properties and mechanical performance to improve their survival ability. Thus, by ingenious structure configuration, lightweight structural biomaterials with simple components can achieve high mechanical performance. This review comprehensively summarizes recent advances in three typical structures in natural biomaterials: cellular structures, fibrous structures, and sandwich structures. For each structure, typical organisms are selected for comparison, and their compositions, structures, and properties are discussed in detail, respectively. In addition, bioinspired design approaches of each structure are briefly introduced. At last, the outlook on the design and fabrication of bioinspired composites is also presented to guide the development of advanced composites in future practical engineering applications.

Gold Nanobipyramid-Mediated Apoptotic Camouflage of Adipocytes for Obesity Immunotherapy.

Obesity treatment is a global public health challenge due to inadequate weight loss and weight regain even after endeavors with multimodal treatments. Considering the abundance of resident macrophages in adipose tissues, precise regulation of the interactions between macrophages and adipocytes may provide chances for immunotherapy of obesity. Herein, inspired by the phagocytosis of macrophages to clear apoptotic cells in homeostasis, an immunotherapy strategy for obesity treatment is proposed for the first time through apoptotic camouflage of adipocytes by PA Au BPs to activate macrophages for clearance, where PA Au BPs are gold nanobipyramids engineered with adipose-targeting and apoptotic cell-mimicking functions. During clearance, the macrophage is switched from pro-inflammatory M1 to anti-inflammatory M2, remarkably modulating the immune microenvironment of adipose tissues to prevent weight regain. After inguinal injection with PA Au BPs, the body weights of obese mice are effectively decreased by 24.4% and can be decreased by 33.3% when combined with photothermal lipolysis, and little weight regain is associated with these treatments. This study demonstrates that the strategy of camouflaging adipocytes with apoptotic features holds great potential for obesity immunotherapy.

Protocol to construct biomimetic carbon fiber composites with improved interfacial strength.

Weak interfacial strength restricts the mechanical properties of carbon fiber-reinforced composites. Here, inspired by natural hook-groove microstructure system (HGMS) of black kite (Milvus migrans), we detail the steps to construct a biomimetic HGMS based on dopamine-functionalized carbon fibers (CFs) and zinc oxide nanorods (ZnO NRs) using a two-step modification approach. We describe the fabrication of biomimetic carbon fiber composites using vacuum-assisted contact molding (VACM) and subsequent characterization using standard comprehensive mechanical tests techniques. For complete details on the use and execution of this protocol, please refer to Wang et al. (2022).

Comparative Investigation on Improved Aerodynamic and Acoustic Performance of Abnormal Rotors by Bionic Edge Design and Rational Material Selection.

Rotor plays a vital role in the dynamical system of an unmanned aerial vehicle (UAV). Prominent aerodynamic and acoustic performance are a long-term pursuit for the rotor. Inspired by excellent quiet flight characteristics of owls, this work adopted bionic edge design and rational material selection strategy to improve aerodynamic and acoustic performance of the rotor. A reference model of rotor prototype with streamlined edges was firstly generated by reverse engineering method. With inspiration from owl wings and feathers, bionic rotors with rational design on leading and trailing edges were obtained. Original and bionic rotors were fabricated with polyamide PA 12 and Resin 9400 by 3D printing technique. Aerodynamic and acoustic performance of the as-fabricated rotors were experimentally measured and analyzed in detail using a self-established test system. Comparative experimental results indicated that the aerodynamic and acoustic performance of the rotors was closely related to the bionic structures, material properties, and rotational speeds. At the same rotational speed, bionic rotor fabricated with Resin 9400 can produce a higher thrust than the prototype one and its power consumption was also reduced. The resulting noise of different bionic rotors and their directivities were comparatively investigated. The results verified the bionic edge design strategy can effectively control the turbulent flow field and smoothly decompose the airflow near the tailing edge, which resulting in enhancing the thrust and reducing the noise. This work could provide beneficial inspiration and strong clues for mechanical engineers and material scientists to design new abnormal rotors with promising aerodynamic and acoustic performance.

Porous morphology and graded materials endow hedgehog spines with impact resistance and structural stability.

Hedgehog spines with evolved unique structures are studied on account of their remarkable mechanical efficiency. However, because of limitations of existing knowledge, it remains unclear how spines work as a material with a balance of stiffness and toughness. By combining qualitative three-dimensional (3D) structural characterization, material composition analysis, biomechanical analysis, and parametric simulations, the relationship between microstructural characteristic and multifunctional features of hedgehog spines is revealed here. The result shows that the fibers transform from the outer cortex to the interior cellular structures by the "T" section composed of the "L" section and a deltoid. The outer cortex, however, shows an arrangement of a layered fibrous structure. An inward change in Young's moduli is observed. In addition, these spines are featured with a sandwich structure that combines an inner porous core with an outer dense cortex. This feature confirms that the hedgehog spines are a kind of biological functionally graded fiber-reinforced composite. Biomimetic models based on the spine are then built, and the corresponding mechanical performance is tested. The results confirm that the internal cellular structure of the spine effectively improve impact resistance. Furthermore, the transverse diaphragm can prevent ellipticity, which may delay buckling. The longitudinal stiffeners also contribute to promote buckling resistance. The design strategies of the spine proposed here provide inspirations for designing T-joint composites. It also exhibits potential applications in low-density, impact and buckling resistance artificial composites. STATEMENT OF SIGNIFICANCE: The spines of a hedgehog are its protective armor that combines strength and toughness. The animal can not only withstand longitudinal and radial forces that are 1 × 106∼ 3 × 106 times the gravity generated by its own weight, but it can also survive unscathed by elastic buckling while dropping to the ground at a speed of up to 15 m/s. Here, we first demonstrate that hedgehog spines are biological graded fiber-reinforced structural composites and reveal their superior impact and buckling resistance mechanism through simulation analysis. Our results broaden the understanding of the relationship among morphology, materials, and function of hedgehog spines. It is anticipated that the survival strategies of hedgehog revealed here could provide inspirations for the development of synthetic composites with impact resistance and structural stability.

Interfacial reinforced carbon fiber composites inspired by biological interlocking structure.

Weak interfacial activity and poor wettability between fiber and matrix are known to be the two main factors that restrict the mechanical properties of carbon fiber-reinforced composites (CFRCs). Herein, inspired by high strength and toughness characteristics of wing feathers of Black Kite (Milvus migrans), natural hook-groove microstructure system (HGMS) and underlying mechanical interlocking mechanism were carefully investigated. Biomimetic HGMS based on dopamine-functionalized carbon fibers and ZnO nanorods were constructed successfully by a two-step modification method to enhance interfacial adhesion. Further, CFRCs featured with biomimetic HGMS were prepared by a vacuum-assisted contact molding method. Experimental results confirmed that flexural strength and interlaminar shear strength of the bioinspired CFRCs were effectively improved by 40.02 and 101.63%, respectively. The proposed bioinspired design strategy was proved to be flexible and effective and it was anticipated to provide a promising design approach and facile fabrication method for desirable CFRCs with excellent mechanical properties.

Bioinspired, Omnidirectional, and Hypersensitive Flexible Strain Sensors.

Sensors are widely used in various fields, among which flexible strain sensors that can sense minuscule mechanical signals and are easy to adapt to many irregular surfaces are attractive for structure health monitoring, early detection, and failure prevention in humans, machines, or buildings. In practical applications, subtle and abnormal vibrations generated from any direction are highly desired to detect and even orientate their directions initially to eliminate potential hazards. However, it is challenging for flexible strain sensors to achieve hypersensitivity and omnidirectionality simultaneously due to the restrictions of many materials with anisotropic mechanical/electrical properties and some micro/nanostructures they employed. Herein, it is revealed that the vision-degraded scorpion detects subtle vibrations spatially and omnidirectionally using a slit sensillum with fan-shaped grooves. A bioinspired flexible strain sensor consisting of curved microgrooves arranged around a central circle is devised, exhibiting an unprecedented gauge factor of over 18 000 and stability over 7000 cycles. It can sense and recognize vibrations of diverse input waveforms at different locations, bouncing behaviors of a free-falling bead, and human wrist pulses regardless of sensor installation angles. The geometric designs can be translated to other material systems for potential applications including human health monitoring and engineering failure detection.

Large-Scale Bio-Inspired Flexible Antireflective Film with Scale-Insensitivity Arrays.

Natural creatures can always provide perfect strategies for excellent antireflection (AR), which is valuable for photovoltaic industry, optical devices, and flexible displays. However, limited by precision, it is still difficult to guarantee the consistency between the artificial structures and the original biological structures. Here, a novel large-scale flexible AR film is inspired by the cicada wings and successfully fabricated with a recycled template. On the one hand, the adjustable structures on porous templates make it possible to optimize the design of AR structure parameters toward the practical demand. On the other hand, it breaks the limitation of the biological organism size, accomplishing the replication of AR nanostructure units in a large scale. Interestingly, even if the film is covered by enlarged dome cone arrays, it still maintains almost perfect AR property, achieving excellent scale-insensitivity AR performance. This work numerically and experimentally investigates its scale-insensitivity AR performance in detail. Compared with subwavelength nanocones, enlarged cones change the original optical behaviors, and the proportion of transmitted light is reduced while scattering and absorption increase. Based on this, these bio-inspired scale-insensitivity AR arrays could be used in flexible displays, photothermic conversion, solar cells, and so on.

Underwater writable and heat-insulated paper with robust fluorine-free superhydrophobic coatings.

Since its invention invented in China, paper has been widely used in the world for quite a long time. However, some intrinsic defects servely hinder its application in some extreme conditions, such as underwater or in fire. Herein, a bio-inspired durable paper with robust fluorine-free coatings was fabricated via a two-step spray-deposition technique. It not only consisted of modified SiO2 microspheres and nanoparticles, but also contained an epoxy resin, endowing the paper with multifunctional properties. First, this bio-inspired functional paper showed excellent superhydrophobic and self-cleaning properties with a high static water contact angle (WCA) of 162.7 ± 0.5° and a low sliding angle (SA) of 5.7 ± 0.6°. Moreover, it possessed unusual repellent properties toward multiple aqueous-based liquids and heat-insulated properties. Second, this paper could be used for writing underwater and maintained satisfactory superhydrophobic performance for a long time with a WCA of 153.3 ± 1.8°. Besides, its high mechanical robustness was also experimentally confirmed in harsh working conditions, such as strong acid/alkali, boiling water, abrasion, bending, and folding. Compared with conventional paper, it is anticipated that this bio-inspired functional paper would be really competitive and demonstrate great potential in the field of underwater and fire-proof applications.

Bioinspired Omnidirectional Self-Stable Reflectors with Multiscale Hierarchical Structures.

Structured surfaces, demonstrating various wondrous physicochemical performances, are ubiquitous phenomena in nature. Butterfly wings with impressive structural colors are an interesting example for multiscale hierarchical structures (MHSs). However, most natural structural colors are relatively unstable and highly sensitive to incident angles, which limit their potential practical applications to a certain extent. Here, we reported a bioinspired color reflector with omnidirectional reflective self-stable (ORS) properties, which is inspired by the wing scales of Papilio palinurus butterfly. Through experimental exploration and theoretical analysis, it was found that the vivid colors of such butterfly wings are structure-based and possess novel ORS properties, which attributes to the multiple optical actions between light and the complex structures coupling the inverse opal-like structures (IOSs) and stacked lamellar ridges (SLRs). On the basis of this, we designed and successfully fabricated the SiO2-based bioinspired color reflectors (BCRs) through a facile and effective biotemplate method. It was confirmed that the MHSs in biotemplate are inherited by the obtained SiO2-based BCRs. More importantly, the SiO2-based BCRs also demonstrated the similar ORS properties in a wide wavelength range. We forcefully anticipate that the reported MHS-based ORS performance discovered in butterfly wing scales here could offer new thoughts for scientists to solve unstable reflection issues in particular optical field. The involved biotemplate fabrication method offers a facile and effective strategy for fabricating functional nanomaterials or bioinspired nanodevices with 3D complex nanostructures, such as structured optical devices, displays, and optoelectronic equipment.

Energy-Efficient Oil-Water Separation of Biomimetic Copper Membrane with Multiscale Hierarchical Dendritic Structures.

Membrane-based materials with special surface wettability have been applied widely for the treatment of increasing industrial oily waste water, as well as frequent oil spill accidents. However, traditional technologies are energy-intensive and limited, either by fouling or by the inability of a single membrane to separate all types of oil-water mixtures. Herein, a biomimetic monolayer copper membrane (BMCM), composed of multiscale hierarchical dendritic structures, is cleverly designed and successfully fabricated on steel mesh substrate. It not only possesses the ability of energy-efficient oil-water separation but also excellent self-recovery anti-oil-fouling properties (<150 s). The BMCM even keeps high separation efficiency (>93%) after ten-time cycling tests. More importantly, it retains efficient oil-water separation capacity for five different oils. In fact, these advanced features are benefited by the synergistic effect of chemical compositions and physical structures, which is inspired by the typical nonwetting strategy of butterfly wing scales. The findings in this work may inspire a facile but effective strategy for repeatable and antipollution oil-water separation, which is more suitable for various applications under practical conditions, such as wastewater treatment, fuel purification, separation of commercially relevant oily water, and so forth.

Active Antifogging Property of Monolayer SiO2 Film with Bioinspired Multiscale Hierarchical Pagoda Structures.

Antifogging surfaces with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, a major challenge remains in achieving high-speed antifogging performance and revealing the hydrophilic-based antifogging mechanism of glass or other transparent materials under aggressive fogging conditions. Herein, with inspiration from the fog-free property of the typical Morpho menelaus terrestris butterfly (Butler, 1866) wing scales, a monolayer SiO2 film with multiscale hierarchical pagoda structures (MHPSs) based on glass substrate was designed and fabricated using an optimized biotemplate-assisted wet chemical method without any post-treatments. The biomimetic monolayer film (BMF) composed of nanoscale SiO2 3D networks displayed excellent antifogging properties, which is superior to that of the glass substrate itself. The MHPS-based BMF even kept high transmittance (∼95%) under aggressive fog conditions, and it almost instantaneously recovered to a fog-free state (<5 s). Moreover, the underlying active antifogging strategy gathering initial fog capture and final antifog together was revealed. The fogdrops spontaneously adhered on the BMF surface and rapidly spread along the MHPSs in an anisotropic way, which made the fogdrops evaporate instantaneously to attain an initial fog-free state, leading to an efficient active antifogging performance. These properties mainly benefit from the synergistic effect of both hydrophilic chemical compositions (nanoscale SiO2) and physical structures (biomimetic MHPSs) of the BMF. High-speed active antifogging performance of the glass materials enabled the retention of a high transmittance property even in humid conditions, heralding reliable optical performance in outdoor practical applications, especially in aggressive foggy environments. More importantly, the investigations in this work offer a promising way to handily design and fabricate quasi-textured surfaces with multiscale hierarchical structures that possess high-performance physicochemical properties.

Biomimetic multifunctional surfaces inspired from animals.

Over millions of years, animals have evolved to a higher intelligent level for their environment. A large number of diverse surface structures on their bodies have been formed to adapt to the extremely harsh environment. Just like the structural diversity existed in plants, the same also applies true in animals. Firstly, this article provides an overview and discussion of the most common functional surface structures inspired from animals, such as drag reduction, noise reduction, anti-adhesion, anti-wear, anti-erosion, anti-fog, water capture, and optical surfaces. Then, some typical characteristics of morphologies, structures, and materials of the animal multifunctional surfaces were discussed. The adaptation of these surfaces to environmental conditions was also analyzed. It mainly focuses on the relationship between their surface functions and their surface structural characteristics. Afterwards, the multifunctional mechanisms or principles of these surfaces were discussed. Models of these structures were provided for the development of structure materials and machinery surfaces. At last, fabrication techniques and existing or potential technical applications inspired from biomimetic multifunctional surfaces in animals were also discussed. The application prospects of the biomimetic functional surfaces are very broad, such as civil field of self-cleaning textile fabrics and non-stick pots, ocean field of oil-water separation, sports field of swimming suits, space development field of lens arrays.

A High-Transmission, Multiple Antireflective Surface Inspired from Bilayer 3D Ultrafine Hierarchical Structures in Butterfly Wing Scales.

A high-transmission, multiple antireflective surface inspired by bilayer 3D ultrafine hierarchical structures in butterfly wing scales is fabricated on a glass substrate using wet chemical biomimetic fabrication. Interestingly, the biomimetic antireflective surface exhibits excellent antireflective properties and high transmission, which provides better characteristics than the butterfly wings and can significantly reduce reflection without losing transparency. These findings offer a new path for generating nanostructured antireflectors with high transmission properties.

An Ingenious Super Light Trapping Surface Templated from Butterfly Wing Scales.

Based on the super light trapping property of butterfly Trogonoptera brookiana wings, the SiO2 replica of this bionic functional surface was successfully synthesized using a simple and highly effective synthesis method combining a sol-gel process and subsequent selective etching. Firstly, the reflectivity of butterfly wing scales was carefully examined. It was found that the whole reflectance spectroscopy of the butterfly wings showed a lower level (less than 10 %) in the visible spectrum. Thus, it was confirmed that the butterfly wings possessed a super light trapping effect. Afterwards, the morphologies and detailed architectures of the butterfly wing scales were carefully investigated using the ultra-depth three-dimensional (3D) microscope and field emission scanning electronic microscopy (FESEM). It was composed by the parallel ridges and quasi-honeycomb-like structure between them. Based on the biological properties and function above, an exact SiO2 negative replica was fabricated through a synthesis method combining a sol-gel process and subsequent selective etching. At last, the comparative analysis of morphology feature size and the reflectance spectroscopy between the SiO2 negative replica and the flat plate was conducted. It could be concluded that the SiO2 negative replica inherited not only the original super light trapping architectures, but also the super light trapping characteristics of bio-template. This work may open up an avenue for the design and fabrication of super light trapping materials and encourage people to look for more super light trapping architectures in nature.