Nanoscale morphology and indentation of individual nacre tablets from the gastropod mollusc Trochus niloticus

The inner nacreous layer of gastropod mollusc Trochus niloticus is composed of similar to 95 wt% planar arrays of polygonal aragonite-based tablets (similar to 8 mu m wide, -0.9 mu m thick, stacked similar to 40 nm apart) and similar to 5 wt% biomacromolecules. High-resolution tapping mode atomic force microscope images enabled nanoscale resolution of fractured tablet cross-sections, the organic component, and deformation of individual nanoasperities on top of tablet surfaces. Nanoindentation was performed on individual nacre tablets and the elastic modulus E and yield stress cry were reduced from elastic-plastic finite element simulations yielding E = 92 GPa, sigma(y) = 11 GPa (freshly cleaved samples) and E = 79 GPa, cry = 9 GPa (artificial seawater soaked samples). Images of the indents revealed extensive plastic deformation with a clear residual indent and surrounding pileup.