Microstructural hierarchy ofEuplectella aspergillum: mechanical insights and biomimetic applications.

Euplectella aspergillum(E.a.) is a remarkable deep-sea glass sponge that has attracted attention from researchers across various disciplines. This review paper provides a comprehensive overview of E.a., focusing on its unique structural and mechanical properties. This sponge species is found mostly in the Pacific Ocean's deep waters at depths ranging from 100 to 1000 m. They have complicated hierarchical structures that span the nanoscale to the macroscale. The sponge's cylindrical, lattice-like structure is made up of silica spicules arranged in a square grid pattern and strengthened by diagonal and helical components. The composition and geometry of individual spicules are also summarised and discussed. Each spicule consists of concentric silica layers separated by organic interlayers. This hierarchical structure contributes to the spicules' exceptional mechanical properties, including enhanced bending capacity, tensile strength, and fracture toughness. The review also explores the spicule bundle interlocking system, which provides additional structural integrity to the overall skeleton. This review also gathers and depicts various experimental techniques and modelling approaches used to investigate the mechanical behaviour of E.a., including nanoindentation, and finite element analysis. These studies have revealed toughening mechanisms that allow the sponge to withstand the challenging deep-sea environment. Some real-world applications inspired by E.a.'s structure, with great potential in architectural designs and advanced materials for the aerospace and automotive industries, are highlighted.