Biomineral Structure and Strength of Barnacle Exoskeletons

The process of building organic-inorganic compound structures through biomineralization is extremely impressive and potentially very useful. During biomineral formation, organisms restructure simple, naturally occurring minerals in conjunction with their own organically produced minerals to create new structures, the functions of which often include protection or storage, among others. While there is extensive knowledge about materials properties and structure of the raw minerals themselves, insight into how specific biomineral structures and compounds contribute to an object’s mechanical properties is lacking. In this study, the exoskeletons of several barnacles from the genus Balanus were examined thoroughly, both for their physical structure (how they’re put together) and for their mechanical properties (tensile strength, hardness, and elasticity). Barnacles were chosen because of their abundance in salt-water environments; their early appearance in the fossil record; and their impact on the early studies of evolution. Scanning electron microscopy produced close-up, detailed images of the inner shell structure to determine what type of structure barnacles build during exoskeleton formation. In addition, energy dispersive x-ray spectroscopy was used to map the elemental components of the shells. Nanoindentation tested the mechanical properties of these mapped structures to determine how certain characteristics of the exoskeleton contribute to its hardness, strength, and elasticity.