Role of layered architecture in marine sponge root fibres: new lessons from nature for the design of tension cables

Patterns found in structural materials of biological origin are an excellent source of inspiration for engineers. The root fibres (basalia spicules) of the marine sponge <i>Euplectella aspergillum</i> anchor it to the ocean floor and exhibit a lamellar architecture. It is generally thought that the spicule's architecture contributes to the spicule's fracture toughness. However, in recent experiments, the spicules' architecture did not contribute to their fracture toughness in a statistically significant way, with their fracture initiation toughness being similar to that of synthetic glass. In this article, we present a mechanics model and show that the spicule's architecture could be contributing to its strength, potentially benefiting the sponge's survival. When a spicule forms a loop, we find that its layers can increase the spicule's strength by reducing the bending stress induced by the tensile load transmitted along its length.