Effect of lattice strain on chitin birefringence

Arthropod cuticle is a biological composite material consisting of chitin fibrils embedded in a protein matrix. It plays a role as an exoskeleton and is also used in dioptrical systems as a lens. Multiple cuticle modifications to adjust the properties to its specific function have been reported, such as metal ion incorporation, hydration, chitin fiber orientation and halogen doping. These modifications not only affect the macroscopic material properties but may also act on the chitin crystallite lattice. Previous results show minute lattice strains of chitin c-axis across horseshoe crab cornea, when measured in dry conditions, which may increase the chitin birefringence affecting the overall optical properties of the lens. Using high resolution scanning WAXS to obtain complementary data under hydrated conditions will help understanding the fundamental relationships in natural chitin-based materials and pave the way for tuning anisotropic properties for synthetic fibrous materials.