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In this paper, the effect of stereom structure on the mechanical behavior of the Sea Urchin Inorganic Skeleton (SUIS) has been studied. The stereom microstructure of both Anthocidaris crassispina and Tripnenstes gratilla was characterized by Scanning Electron Microscopy (SEM). Results indicate that a three-layer porous structure consisting of a growth, a support, and a resorption (GSR) layer is a common denominator for both species. The effect of GSR layer order on the mechanical behavior of the SUIS was studied by a finite element method. The results show that the GSR model could effectively reduce the maximum tensile stress on its meridional sutures under unidirectional pressure, hydrostatic pressure, and self-weight situation. For a fabricated three-layered ceramic test strips with different layer orders, the mechanical properties have a completely opposite performance compared with the compressive properties of the calculated SUIS-like models. This indicates that the GSR structure can effectively improve the mechanical properties of the SUIS, but it cannot be applied to bionics without considering its synergistic effect with the macro-structure of the SUIS. This is a typical example of bionic invalidation by single structure, where multi-level structure bionics may be an effective solution.

The spines of pencil and lance urchins Heterocentrotus mammillatus and Phyllacanthus imperialis were studied as a model of light-weight material with high impact resistance. The complex and variable skeleton construction (“stereom”) of body and spines of sea urchins consists of highly porous Mg-bearing calcium carbonate. This basically brittle material with pronounced single-crystal cleavage does not fracture by spontaneous catastrophic device failure but by graceful failure over the range of tens of millimeter of bulk compression instead. This was observed in bulk compression tests and blunt indentation experiments on regular, infiltrated and latex coated sea urchin spine segments. Microstructural characterization was carried out using X-ray computer tomography, optical and scanning electron microscopy. The behavior is interpreted to result from the hierarchic structure of sea urchin spines from the macroscale down to the nanoscale. Guidelines derived from this study see ceramics with layered porosity as a possible biomimetic construction for appropriate applications.