The importance of water for the mechanical properties of insect cuticle

摘要

Insect cuticle has a broad range of mechanical properties. As it has to provide a very efficient and lightweight skeleton, cuticle is a highly interesting composite-material and may serve as a natural model for new biomimetic materials. However, the water content of insect cuticle is of great importance for its material properties. Here, we present a new method to perform nano-indentation experiments in cuticle which has its full water content. Parts of the exoskeleton of Locusta migratoria were investigated to determine the elastic modulus (Er) and hardness (H) of the cuticle. Cuticle sections were measured in air and then submerged and measured in water. As insect cuticle is an anisotropic material, we performed nano-indentation in the normal as well as in the transverse direction and also tested different cuticle layers within each sample (exo-, meso- and endo-cuticle). It turned out that a change of the water content has a dramatic impact on the material properties of the cuticle. For example, the Er of submerged endo-cuticle turned out to be 75% lower than of endo-cuticle samples measured in air. Further, the proportion of material property values between different cuticle layers within a sample change dramatically after addition of water.