Characteristics of the tensile mechanical properties of fresh and dry forewings of beetles

Structure and mechanical properties of ladybird elytra as biological sandwich panels

The armour of the ladybird, elytra, protect the body from injury and are well-adapted to flight. However, experimental methods to decipher their mechanical performances had been challenging due to the small size, making it unclear how the elytra balance mass and strength. Here, we provide insights to the relationship between the microstructure and multifunctional properties of the elytra by means of structural characterization, mechanical analysis and finite element simulations. Micromorphology analysis on the elytron revealed the thickness ratio of the upper lamination, middle layer and lower lamination is approximately 51:139:7. The upper lamination had multiple cross fibre layers and the thickness of each fibre layer is not the same. In addition, the tensile strength, elastic modulus, fracture strain, bending stiffness and hardness of elytra were obtained through in-situ tensile and nanoindentation-bending under the influence of multiple loading conditions, which also serve as references for finite element models. The finite element model revealed that structural factors such as thickness of each layer, angle of fibre layer and trabeculae are key to affecting the mechanical properties, but the effect is different. When the thickness of upper, middle and lower layers is the same, the tensile strength provided by unit mass of the model is 52.78% lower than that provided by elytra. These findings broaden the relationship between the structural and mechanical properties of the ladybird elytra, and are expected to inspire the development of sandwich structures in biomedical engineering.

The draft genome sequence of the Japanese rhinoceros beetle Trypoxylus dichotomus septentrionalis towards an understanding of horn formation

The Japanese rhinoceros beetle Trypoxylus dichotomus is a giant beetle with distinctive exaggerated horns present on the head and prothoracic regions of the male. T. dichotomus has been used as a research model in various fields such as evolutionary developmental biology, ecology, ethology, biomimetics, and drug discovery. In this study, de novo assembly of 615 Mb, representing 80% of the genome estimated by flow cytometry, was obtained using the 10 × Chromium platform. The scaffold N50 length of the genome assembly was 8.02 Mb, with repetitive elements predicted to comprise 49.5% of the assembly. In total, 23,987 protein-coding genes were predicted in the genome. In addition, de novo assembly of the mitochondrial genome yielded a contig of 20,217 bp. We also analyzed the transcriptome by generating 16 RNA-seq libraries from a variety of tissues of both sexes and developmental stages, which allowed us to identify 13 co-expressed gene modules. We focused on the genes related to horn formation and obtained new insights into the evolution of the gene repertoire and sexual dimorphism as exemplified by the sex-specific splicing pattern of the doublesex gene. This genomic information will be an excellent resource for further functional and evolutionary analyses, including the evolutionary origin and genetic regulation of beetle horns and the molecular mechanisms underlying sexual dimorphism.

Tensile mechanical properties and finite element simulation of the wings of the butterfly Tirumala limniace

This study examined the morphological characteristics and mechanical properties of the wings of Tirumala limniace. The wings of this butterfly, including the forewings and hindwings, are composed mainly of a flexible wing membrane and supporting wing veins. Scanning electron microscopy was employed to observe specific positions of the wing membrane and veins and reveal the morphological characteristics. Tensile experiments were conducted to evaluate the mechanical properties of the wings and proved that the multifiber layer structures have a significantly fixed orientation of fiber alignment. A butterfly wing model reconstructed in reverse based on the finite element method was used to analyze the static characteristics of the wing structure in detail. Evaluation of stress and strain after applying uniform loading, perpendicular loading, and torsion revealed that minor wing deformation occurred and was concentrated near the main wing vein, which verifies the steadiness of the butterfly wing structure. Additionally, the flapping of butterfly wings was simulated using computational fluid dynamics to study the flow field near the butterfly wings and the distribution of pressure gradient on the wings. The results confirmed the effect of wing veins on maintaining the flight performance.

Enhancing Bioinspired Aramid Nanofiber Networks by Interfacial Hydrogen Bonds for Multiprotection under an Extreme Environment

In nature, many insects have evolved sclerotic cuticles to shelter their soft bodies, which are considered as "body armor". For beetles, the epidermis is composed of cross-linked intertwined fiber structures; such a fiber network structure could provide an anti-impact function for composites. Aramid nanofibers (ANFs) are of great interest in various applications due to their 1D nanoscale, high aspect ratio, excellent strength and modulus, and impressive chemical and thermal stability. In this paper, a kind of ANF network is prepared by a layer-by-layer assembly method. The enhancing ANF networks are developed by introducing carboxylated chitosan acting as a hydrogen-bondin donors as well as a soft interlocking agent (C-ANFs). As a result of the formation of a nanostructure and the hydrogen-bond interactions, the assembled C-ANF networks presented a high tensile strength (551.4 MPa) and toughness (4.0 MJ/m²), which is 2.41 times and 32.69 times those of neat ANF networks, respectively. The excellent mechanical properties endow C-ANF networks with distinguished anti-impact performance. The specific dissipated energy after mass normalization reaches 7.34 MJ/kg, which is significantly superior to traditional protective materials such as steel and Kevlar composites. A nonlinear spring model is also used to explain the mechanical behavior of C-ANF networks. In addition to anti-impact protection, C-ANF networks can realize more than 99% of UV irradiation absorption and have excellent thermal stability. The chemical stability of C-ANF networks make them survive in acid and alkali environments. The above characteristics show that C-ANF networks have great application value in multiscale protection scenarios under an extreme environment.

The forewing of a black cicada Cryptotympana atrata (Hemiptera, Homoptera: Cicadidae): Microscopic structures and mechanical properties

Insects in nature flap their wings to generate lift force and driving torque to adjust their attitude and control stability. An insect wing is a biomaterial composed of flexible membranes and tough veins. In this paper, we study the microscopic structures and mechanical properties of the forewing of the black cicada, Cryptotympana atrata. The thickness of the wing membranes and the diameter of veins varied from the wing root to the tip. The thickness of the wing membranes ranged from 6.0 to 29.9 μm, and the diameter of the wing veins decreased in a gradient from the wing root to the tip, demonstrating that the forewing of the black cicada is a nonuniform biomaterial. The elastic modulus of the membrane near the wing root ranged from 4.45 to 5.03 GPa, which is comparable to that of some industrial membranes. The microstructure of the wing vein exhibited a hollow tubular structure with flocculent structure inside. The "fresh" sample stored more water than the "dry" sample, resulting in a significant difference in the elastic modulus between the fresh and dried veins. The different membrane thicknesses and elastic moduli of the wing veins near the root and tip resulted in varied degrees of deformation on both sides of the flexion line of the forewing during twisting. The measurements of the forewing of the cicada may serve as a guide for selecting airfoil materials for the bionic flapping-wing aircraft and promote the design and manufacture of more durable bionic wings in the future.

Recent advances in understanding horn formation in the Japanese rhinoceros beetle Trypoxylus dichotomus using next-generation sequencing technology

The exaggerated horns of beetles are attractive models for studying the origin of novel traits and morphological evolution. Closely related species often differ profoundly in the size, number, and shape of their horns, and in the body region from which they extend. In addition, beetle horns exhibit exquisite nutrition-dependent phenotypic plasticity, leading to disproportionate growth of the horns in the largest, best-condition individuals and much smaller - even stunted - horn sizes in poor-condition individuals. These exciting phenomena in beetle horns have recently been revealed at the molecular level with the advent of next-generation sequencing. This section reviews the latest research on a horned beetle, the Japanese rhinoceros beetle Trypoxylus dichotomus, whose genome was recently sequenced.