Characterization of the Widescale Reversible Sliding Mechanism in California Red Abalone Nacre Structure

Abstract

The precise and ordered microstructures produced through the bottom-up process of self-assembly is a matter of much interest to many research teams, with many applications in the fields of engineering and technology. In the realm of biology, many organisms have developed some form of a self-assembly process to fit a physiological need over millions of years of evolution. One such example of this is the growth of the nacreous shell of the abalone. This research focuses on the abalone nacre and the mechanical properties of the structure. Nacre, commonly referred to as “mother of pearl”, makes up the iridescent inner portion of the abalone’s shell and is an integral component. The nacre is comprised of nanoscale aragonite calcium carbonate tablets arranged in a “coin stack” manner. These tablets are grown through the self-assembly process known as biomineralization, in which a colloidal organic liquid is secreted from the epithelial cells of the abalone between their body and the outer wall of their shell. As the tablets grow, the organic liquid become the organic matrix that is interlocked throughout the entire tablet structure, creating a unique composite material with fascinating properties. These properties have been researched extensively, including the excellent strength provided by the material as well as the deformation mechanism of tablet sliding. But one aspect which has had little to no attention paid to it is the potential for a self-recovery mechanism that may be present in the nacre structure. The goal of this work is to observe the presence of and characterize this widescale reversible sliding mechanism in the nacre structure of the California wild red abalone. To test for the presence of this mechanism, rectangular nacre beams were sectioned from shells of California red abalone. These nacre beams were polished along the cross-sectional side to reveal the tablet structure. The beams were then placed into a scanning electron microscope and subjected to an in situ three-point bending experiments in an attempt to reveal this mechanism. Further analysis of this mechanism was performed by applying a nano scale speckle pattern and performing digital image correlation, to view the mechanism on a local level.