Anisotropic alignment and mechanical properties of chitin nanofibers in marine hydroid perisarc

The exoskeleton of the marine hydroid Aglaophenia latirostris exhibits exceptional mechanical properties despite its low mineral content, providing valuable insights for the design of advanced biomaterials. In this study, we used polarized Raman spectroscopy and nanoindentation techniques to investigate the alignment and mechanical characteristics of chitin nanofibers in the hydroid perisarc. The chitin nanofibers demonstrated anisotropic alignment, which significantly contributed to the stiffness of the anisotropic hydroid’s perisarc in dry conditions (Young’s modulus of 5.16 GPa). Although the mechanical performance deteriorated in wet conditions, the perisarc still exhibited a higher Young’s modulus (0.61 GPa) and hardness (0.07 GPa) compared with isotropic chitin/chitosan (purified) in the wet state. The hydrated proteins in the perisarc dissipated stress, a feature absent in isotropic chitin. The increase in flexibility due to hydration indicates a biological adaptation of the hydroid to its marine environment, allowing it to balance mechanical strength with resilience in a dynamic, wet environment. The hierarchical structure of the hydroid’s exoskeleton allows it to function in both wet and dry environments, offering high stiffness and flexibility. These findings highlight the potential applications of this structure for developing biomimetic materials capable of functioning under varying moisture levels.