Shells*

Biological evolution has achieved the ultimate optimization of material structure, properties, and performance which can be an inspiration for many biomimetic materials. Most biological materials are hierarchical structures consisting of an inorganic and a small quantity of polymeric component. Several combinations of these materials form the enormous hybrid structures observed in nature. Among the various biological materials, shells are of intense mechanical interest for its remarkable strength and toughness. Anomia ephippium, commonly known as “jingle shells” is nearly optically transparent and exhibit colored hues ranging from white to orange to dark black, which is due to the presence of polyenes. We have studied the full stiffness tensor and elastic properties of A. ephippium as determined using Brillouin scattering, which is a non-invasive tool. Our studies show that the presence of pigments influences the mechanical properties of the shell, which is unusual for an organism exhibiting color polymorphism. We have also studied the influence of microstructure on the elastic properties of the shells by comparing the nacre and prismatic layers of red abalone with the foliated calcite structure of A. ephippium.