Multiscale designs of the chitinous nanocomposite of beetle horn towards an enhanced biomechanical functionality

Nature's loom: How to design a spinning tool using chitin-protein based composite material

Silk-producing animals use spigots to generate natural silk fibers for various purposes. These natural looms must be able to withstand prolonged silk extrusion. To gain insight into the functional basis of spigots, we report on the structural design of the spigot of the silkworm Bombyx mori. The B. mori spigot exhibits a unique triple-ridged strip surface structure, consisting of cuticle proteins, resilin, chitin, and metal ions (such as K and Ca). This multi-microstructure endows the spigot with superior hierarchical mechanical properties, enabling it to function as a spinning tool for silk formation, thereby influencing the structure and performance of the silk. These findings demonstrate new pathways for achieving specialized functions in confined spaces, providing theoretical support for understanding the natural spinning mechanism and inspiring new directions for developing innovative biomimetic materials.

The beetle's structural protein CPCFC making elytra tough and rigid

The insect cuticle, which serves as both a protective barrier and an efficient lever system for locomotion, is an extracellular matrix primarily composed of chitin and protein. The cuticle protein CPCFC characterized by a "CFC" motif containing 2 Cys split by the insertion of 5 residues is distributed across most insect species and specifically localized in the hard part of the cuticle. However, their physiological function is not fully understood. Here, we report 2 CPCFC proteins, TcCPCFC1 and TcCPCFC2, derived from the Coleopteran insect Tribolium castaneum. We revealed that TcCPCFC1 and TcCPCFC2 were predominantly expressed during the larval and adult stages of T. castaneum, respectively. The transcription downregulation of TcCPCFC1 significantly decreased the modulus and toughness of the elytral cuticle. We found that TcCPCFC proteins have high binding affinity to chitin. We cloned and produced recombinant TcCPCFC proteins and demonstrated that the addition of TcCPCFC proteins to chitin hydrogel greatly enhanced the hydrogel's modulus and toughness by forming denser chitin fibrous networks. Our findings reveal the functional role of CPCFC proteins in enhancing mechanical properties of insect cuticle, and we validate this process in vitro, and offer a protein candidate for fabrication of advanced chitin-based materials.

Multicopper oxidase-2 mediated cuticle formation: Its contribution to evolution and success of insects as terrestrial organisms

The insect cuticle is a non-cellular matrix composed of polysaccharide chitins and proteins. The cuticle covers most of the body surface, including the trachea, foregut, and hindgut, and it is the body structure that separates the intraluminal environment from the external environment. The cuticle is essential to sustain their lives, both as a physical barrier to maintain homeostasis and as an exoskeleton that mechanically supports body shape and movement. Previously, we proposed a theory about the possibility that the cuticle-forming system contributes to the "evolution and success of insects." The main points of our theory are that 1) insects evolved an insect-specific system of cuticle formation and 2) the presence of this system may have provided insects with a competitive advantage in the early land ecosystems. The key to this theory is that insects utilize molecular oxygen abundant in the atmosphere, which differs from closely related crustaceans that form their cuticles with calcium ions. With newly obtained knowledge, this review revisits the significance of the insect-specific system for insects to adapt to terrestrial environments and also discusses the long-standing question in entomology as to why, despite their great success in terrestrial environments, they poorly adapt to marine environments.

Adaptive structural reorientation: Developing extraordinary mechanical properties by constrained flexibility in natural materials

Seeking strategies to enhance the overall combinations of mechanical properties is of great significance for engineering materials, but still remains a key challenge because many of these properties are often mutually exclusive. Here we reveal from the perspective of materials science and mechanics that adaptive structural reorientation during deformation, which is an operating mechanism in a wide variety of composite biological materials, functions more than being a form of passive response to allow for flexibility, but offers an effective means to simultaneously enhance rigidity, robustness, mechanical stability and damage tolerance. As such, the conflicts between different mechanical properties can be "defeated" in these composites merely by adjusting their structural orientation. The constitutive relationships are established based on the theoretical analysis to clarify the effects of structural orientation and reorientation on mechanical properties, with some of the findings validated and visualized by computational simulations. Our study is intended to give insight into the ingenious designs in natural materials that underlie their exceptional mechanical efficiency, which may provide inspiration for the development of new man-made materials with enhanced mechanical performance. STATEMENT OF SIGNIFICANCE: It is challenging to attain certain combinations of mechanical properties in man-made materials because many of these properties - for example, strength with toughness and stability with flexibility - are often mutually exclusive. Here we describe an effective solution utilized by natural materials, including wood, bone, fish scales and insect cuticle, to "defeat" such conflicts and elucidate the underlying mechanisms from the perspective of materials science and mechanics. We show that, by adaptation of their structural orientation on loading, composite biological materials are capable of developing enhanced rigidity, strength, mechanical stability and damage tolerance from constrained flexibility during deformation - combinations of attributes that are generally unobtainable in man-made systems. The design principles extracted from these biological materials present an unusual yet potent new approach to guide the development of new synthetic composites with enhanced combinations of mechanical properties.