A damage-tolerant, dual-scale, single-crystalline microlattice in the knobby starfish, Protoreaster nodosus

Abstract

Cellular solids (e.g., foams and honeycombs) are widely found in natural and engineering systems because of their high mechanical efficiency and tailorable properties. While these materials are often based on polycrystalline or amorphous constituents, here we report an unusual dual-scale, single-crystalline microlattice found in the biomineralized skeleton of the knobby starfish, Protoreaster nodosus . This structure has a diamond-triply periodic minimal surface geometry (lattice constant, approximately 30 micrometers), the [111] direction of which is aligned with the c -axis of the constituent calcite at the atomic scale. This dual-scale crystallographically coaligned microlattice, which exhibits lattice-level structural gradients and dislocations, combined with the atomic-level conchoidal fracture behavior of biogenic calcite, substantially enhances the damage tolerance of this hierarchical biological microlattice, thus providing important insights for designing synthetic architected cellular solids.

Biomineralized Materials as Model Systems for Structural Composites: 3D Architecture

“…Reproduced with permission. [ 117 ] Copyright 2022, AAAS. b) Honeycomb‐like network in the primary skeletal system of sea sponge Aphrocallistes vastus .…”

“…These porous structures typically have a smooth, continuous surface shape for better transportation performance (Figure 7a). [ 117,118 ] In addition, when the porous structure is partly or fully filled with air, mass reduction or buoyancy can be achieved. [ 26 ] Secondly, porous/bicontinuous structures can gain better crush performance and energy absorption per mass.…”

“…For example, the ossicle of sea star and the spine of sea urchin are single crystals of calcite arranged in a porous microstructure (porosity 0.5–0.7) which exhibit remarkable performance in controlling the fracture pathways. [ 117,118 ] The ability of these materials to serve as robust mechanical support and protection components is largely contributed by their specially architected porous structure. Our recent studies have provided insights into this regard, [ 117,118,121 ] but still, how the lattice structure and morphology of the porous structure should be designed to further improve the fracture toughness remains an open question.…”

“…These materials are typically bicontinuous or porous, examples include the scaffold-like structures of cancellous bones, [12,115] the wall-septum microstructure of cuttlebones, [92,93] the stereom structures of sea urchin spines composed of branches and nodes, [116] and the periodic lattice structures with triply periodic minimal surface (TPMS) in sea star ossicles (Figure 7a-e). [117] Compared to the other three motifs, bicontinuous/porous structures exhibit several distinct structural characteristics.…”

“…[117,118] The ability of these materials to serve as robust mechanical support and protection components is largely contributed by their specially architected porous structure. Our recent studies have provided insights into this regard, [117,118,121] but still, how the lattice structure and morphology of the porous structure should be designed to further improve the fracture toughness remains an open question. [119,122] Fourthly, the basic building blocks of some biomineralized materials possess a continuous single-crystal mineral matrix with discrete nanoscopic organic inclusions.…”