Simple Model for the Toughness of a Helical Structure Inspired by the Exoskeleton of Lobsters

Abstract

Nature has evolved remarkable hierarchical structures to realize tough biocomposites. The helical structure of the exoskeleton generally found in crustaceans is one such example. Recently, detailed structural and mechanical properties of the exoskeleton have been actively studied for lobsters, which has inspired artificial biomineralization. However, the superiority of the special structure giving the toughness has yet to be elucidated. Here, we develop a simple model of the structure of crustaceans via two-step coarse-graining to obtain a scaling law for fracture energy, a measure of fracture toughness. The law provides a clear physical understanding of how the simple model structure is optimized in terms of its the toughness by exploiting at least five important design principles.

Self-Assembled, Iridescent, Crustacean-Mimetic Nanocomposites with Tailored Periodicity and Layered Cuticular Structure

“…In summary, the crack propagation studies demonstrate that an increasing amount of toughening mechanisms occurs with increasing polymer content (ligament bridging, constrained microcracking), which are reminiscent of the biological role model composites. 27,62 Those reflect the increased ability of the materials to undergo plastic deformation with increasing polymer content and when passing from an ordered to a disordered state. Additionally, delamination occurs along planes in the cholesteric structure at the mesoscales.…”

“…Crustacean cuticles contain highly crystalline, reinforcing chitin nanofibrils, which are surrounded by a binding and energy-dissipating protein shell, and are organized in a plywood structure with layers of different periodicity at the inside (endocuticle) and outside (exocuticle) of the shell. Additionally, the structure is slightly mineralized depending on the species, and channels perpendicular to the cuticle can be found. − We focus in our approach for a crustacean mimetic on the cholesteric organization of the plywood structure, the realization of an alternating hard/soft composite structure, and the possibility to tune the periodicity of the helical plywood structure, which we exploit to prepare layered materials with different periodicities as similarly found in the endo- and exocuticles.…”

Supramolecular Engineering of Hierarchically Self-Assembled, Bioinspired, Cholesteric Nanocomposites Formed by Cellulose Nanocrystals and Polymers

“…The cholesteric structure is reminiscent of the plywood structure found in crustacean cuticles (such as lobster), in which highly crystalline, reinforcing chitin nanofibrils are surrounded by a binding energy-dissipating and slightly mineralized protein shell. − Given the strength and toughness of the crustaceans, known from maritime cuisine, it would be highly desirable to pursue such cholesteric nanocomposite structures in advanced biomimetic nanocomposites and integrate them with molecular energy dissipation mechanisms. From previous work, it is know that appropriate coassembly conditions allow the integration of gold nanorods for chiral plasmonics, , or the templation of mesoporous inorganic silica structures and organic resins via cocasting of monomers and subsequent polymerization. − Interestingly enough, reports about direct coassembly of water-soluble polymers and CNCs to make cholesteric bioinspired CNC/polymer nanocomposites are still scarce, although it is possibly the simplest approach. , In addition, photonic properties are more in focus compared to mechanical properties. − One of the central challenges toward direct coassembly is to identify polymers that do not interfere with the formation of the colloidal length scale .…”