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.

Naturally strong but light

Cellular solids such as foams or honeycombs can exhibit excellent stiffness or toughness with minimal weight. Yang et al . examined ossicles, calcareous skeletal elements from the skeletons of knobby starfish (see the Perspective by Hyde and Meldrum). The authors show that the structure consists of a dual-scale microlattice with both atomic-level calcite and micro-level diamond-triply periodic minimal surface, as well as gradients in composition and atomic level defects. It is these combined features that enhance the damage tolerance of the ossicles under compression, giving the starfish remarkable specific energy absorption capabilities. —MSL

Abstract

Knobby starfish construct a skeleton with a periodic porous lattice from single-crystal calcite for enhanced protection.