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 mechanical characterization of the legs, fangs, and prosoma in the spider Harpactira curvipes (Pocock 1897)

The exoskeleton of spiders is the primary structure that interacts with the external mechanical stimuli, thus playing a crucial role in spider life. In particular, fangs, legs, and prosoma are the main rigid structures of the exoskeleton and their properties must be measured to better understand their mechanical behaviours. Here we investigate, by means of nanoindentation, the mechanical properties of the external sclerotized cuticles of such parts in the spider Harpactira curvipes. Interestingly, the results show that the leg's cuticle is stiffer than the prosoma and has a stiffness similar to the one of the tip fangs. This could be explained by the legs' function in perceiving vibrations that could be facilitated by higher stiffness. From a broader perspective, this characterization could help to understand how the same basic material (the cuticle, i.e. mainly composed of chitin) can be tuned to achieve different mechanical functions, which improves the animal's adaptation to specific evolutive requirements. We, thus, hope that this work stimulates further comparative analysis. Moreover, these results may also be potentially important to inspire the design of graded materials with superior mechanical properties.

Mathematical model and nanoindentation properties of the claws of Cyrtotrachelus buqueti Guer (Coleoptera: Curculionidae)

Scanning electron microscopy (SEM) was used to observe the macroscopic, microscopic, and cross‐sectional structures of the claws of Cyrtotrachelus buqueti Guer (Coleoptera: Curculionidae), and a mathematical model of a claw was used to investigate the structure–function relationships. To improve the quality of the SEM images, a non‐local means (NLM) algorithm and an improved NLM algorithm were applied. After comparison and analysis of five classical edge‐detection algorithms, the boundaries of the structural features of the claw were extracted based on a B‐spline wavelet algorithm, and the results showed that the variable curvature of the beetle claw enhances its adhesion force and improves its strength. Adhesion models of the claw were established, and the mechanical properties of its biomaterials were measured using nanoindentation. Considering that the presence of water can affect the hardness and Young's modulus, both ‘dry’ and ‘wet’ samples were examined. For the dry samples, the hardness and Young's modulus were 0.197 ± 0.074 GPa and 1.105 ± 0.197 GPa, respectively, whereas the respective values for the wet samples were both lower at 0.071 ± 0.030 GPa and 0.693 ± 0.163 GPa. This study provides data that can inform the design of climbing robots.

Nanomechanical testing in drug delivery: Theory, applications, and emerging trends

Mechanical properties play a central role in drug formulation development and manufacturing. Traditional characterization of mechanical properties of pharmaceutical solids relied mainly on large compacts, instead of individual particles. Modern nanomechanical testing instruments enable quantification of mechanical properties from the single crystal/particle level to the finished tablet. Although widely used in characterizing inorganic materials for decades, nanomechanical testing has been relatively less employed to characterize pharmaceutical materials. This review focuses on the applications of existing and emerging nanomechanical testing methods in characterizing mechanical properties of pharmaceutical solids to facilitate fast and cost-effective development of high quality drug products. Testing of pharmaceutical materials using nanomechanical techniques holds potential to develop fundamental knowledge in the structure-property relationships of molecular solids, with implications for solid form selection, milling, formulation design, and manufacturing. We also systematically discuss pitfalls and useful tips during sample preparation and testing for reliable measurements from nanomechanical testing.

Investigation of the selective color-changing mechanism of Dynastes tityus beetle (Coleoptera: Scarabaeidae)

Not only does the Dynastes tityus beetle display a reversible color change controlled by differences in humidity, but also, the elytron scale can change color from yellow-green to deep-brown in specified shapes. The results obtained by focused ion beam-scanning electron microscopy (FIB-SEM), show that the epicuticle (EPI) is a permeable layer, and the exocuticle (EXO) is a three-dimensional photonic crystal. To investigate the mechanism of the reversible color change, experiments were conducted to determine the water contact angle, surface chemical composition, and optical reflectance, and the reflective spectrum was simulated. The water on the surface began to permeate into the elytron via the surface elemental composition and channels in the EPI. A structural unit (SU) in the EXO allows local color changes in varied shapes. The reflectance of both yellow-green and deep-brown elytra increases as the incidence angle increases from 0° to 60°. The microstructure and changes in the refractive index are the main factors that influence the process of reversible color change. According to the simulation, the lower reflectance causing the color change to deep-brown results from water infiltration, which increases light absorption. Meanwhile, the waxy layer has no effect on the reflection of light. This study lays the foundation to manufacture engineered photonic materials that undergo controllable changes in iridescent color.

Lessons from mosquitoes' painless piercing

Arthropods are the largest group of the living organisms. They attack other organisms by biting, stinging, or piercing and sucking. Among various medically important arthropods, which feed on living hosts, mosquitoes' piercing spread viruses which have been reported to cause the highest number of deaths annually. The primary cause of the deaths is malaria, which is spread by infected mosquitoes' piercing. This study aims at elucidating lessons from mosquitoes' painless piercing. Mosquitoes pierce using their fascicle, which is a bundle of coherently functioning six stylets. Based on experiments and available literature, it is presented that mosquitoes painlessly pierce using a combination of the numbing, the fascicle's serrated design, the vibratory actuation, and the graded and frequency-dependent mechanical properties of the labrum. Based on this understanding, a mosquito-inspired microneedle design has also been proposed.

The Role of Nanomechanics in Healthcare

Nanomechanics has played a vital role in pushing our capability to detect, probe, and manipulate the biological species, such as proteins, cells, and tissues, paving way to a deeper knowledge and superior strategies for healthcare. Nanomechanical characterization techniques, such as atomic force microscopy, nanoindentation, nanotribology, optical tweezers, and other hybrid techniques have been utilized to understand the mechanics and kinetics of biospecies. Investigation of the mechanics of cells and tissues has provided critical information about mechanical characteristics of host body environments. This information has been utilized for developing biomimetic materials and structures for tissue engineering and artificial implants. This review summarizes nanomechanical characterization techniques and their potential applications in healthcare research. The principles and examples of label-free detection of cancers and myocardial infarction by nanomechanical cantilevers are discussed. The vital importance of nanomechanics in regenerative medicine is highlighted from the perspective of material selection and design for developing biocompatible scaffolds. This review interconnects the advancements made in fundamental materials science research and biomedical technology, and therefore provides scientific insight that is of common interest to the researchers working in different disciplines of healthcare science and technology.

Structural, tribological, and mechanical properties of the hind leg joint of a jumping insect: Using katydids to inform bioinspired lubrication systems

This study investigates the structural properties of the hind leg femur-tibia joint in adult katydids (Orthoptera: Tettigoniidae), including its tribological and mechanical properties. It is of particular interest because the orthopteran (e.g., grasshoppers, crickets, and katydids) hind leg is highly specialized for jumping. We show that the katydid hind leg femur-tibia joint had unique surfaces and textures, with a friction coefficient (μ) at its coupling surface of 0.053±0.001. Importantly, the sheared surfaces at this joint showed no sign of wear or damage, even though it had undergone thousands of external shearing cycles. We attribute its resiliency to a synergistic interaction between the hierarchical surface texture/pattern on the femoral surfaces, a nanograded internal nanostructure of articulating joints, and the presence of lubricating lipids on the surface at the joint interface. The micro/nanopatterned surface of the katydid hind leg femur-tibia joint enables a reduction in the total contact area, and this significantly reduces the adhesive forces between the coupling surfaces. In our katydids, the femur and tibia joint surfaces had a maximum effective elastic modulus (E_eff) value of 2.6GPa and 3.9GPa, respectively. Presumably, the decreased adhesion through the reduction of van der Waals forces prevented adhesive wear, while the contact between the softer textured surface and harder smooth surface avoided abrasive wear. The results from our bioinspired study offer valuable insights that can inform the development of innovative coatings and lubrication systems that are both energy efficient and durable.

STATEMENT OF SIGNIFICANCE

Relative to body length, insects can outjump most animals. They also accelerate their bodies at a much faster rate. Orthopterans (e.g., grasshoppers, crickets, and katydids) have hind legs that are specialized for jumping. Over an individual's lifetime, the hind leg joint endures repeated cycles of flexing and extending, including jumping, and its efficiency and durability easily surpass that of most mechanical devices. Although the efficient functioning of insect joints has long been recognized, the mechanism by which insect joints experience friction/adhesion/wear, and operate efficiently/reliably is still largely unknown. Our study on the structural, tribological, and mechanical properties of the orthopteran hind leg joints reveals the potential of katydid bioinspired research leading to more effective coatings and lubrication systems.

Relationship of hydration and nanomechanical characteristics of beetle cuticle

Insect elytra cuticle has some excellent mechanical properties, such as tenacity, waterproofness and light weight, which are the results of its laminate composite structure. Understanding the unique structural and mechanical characteristics of the elytral cuticle of beetles will facilitate the design of biomimetic composite materials. As the thickness of beetle cuticle can range from the microscale to the nanoscale, investigating the cuticle’s mechanical characteristics is difficult until nanoindentation techniques have been developed. In this study, a nanoindenter was used to explore nanomechanical characteristics, including the reduced modulus (E r) and hardness (H), of the cuticle of the dung beetle Copris ochus Motschulsky. To understand the effect of water on these characteristics, the samples were tested immediately after collection or after different periods of sample ageing. The results showed that the mechanical characteristics were strongly influenced by sample ageing and that E r and H increased with decreasing water content. The results are discussed in the context of how the mechanical characteristics of the cuticle correspond to beetle behaviour.