Structural and nanomechanical insights into the spicules of Euplectella aspergillum

Biomimicry offers sustainable, efficient, and adaptable solutions inspired by natural systems. The skeleton of Euplectella aspergillum (EA) represents a highly optimized biological structure. It is composed of silica-based elements known as spicules, which interlock to form a lattice-like framework that provides strength and flexibility. In this study, the structural and functional properties of EA spicules were investigated. The macrostructure revealed a well-organized, multi-component framework consisting of a filter cap, spiral crest, skeletal wall, and anchor base-features that contribute to hydrodynamic efficiency and mechanical stability. The hierarchical architecture was characterized using scanning electron microscopy, atomic force microscopy (AFM), nanoindentation, thermogravimetric analysis, differential scanning calorimetry, and x-ray diffraction (XRD). At the microscale, spicules exhibited a laminated architecture of silica and organic layers, which redirect crack propagation and dissipate energy, enhancing fracture resistance. Nanoindentation and AFM revealed mechanical properties across the spicule cross-section, with an average hardness of 4.436 ± 0.202 GPa, reduced modulus of 39.596 ± 0.374 GPa, and stiffness of 21.200 ± 0.517<i>µ</i>N nm^-1. Sink-in behavior indicated the elastic and brittle nature of both silica and organic regions. Localized pile-up near organic interfaces highlighted plastic deformation constraints due to mechanical heterogeneity. Thermal analysis identified approximately 9.83% organic content and confirmed high thermal stability of the silica matrix. A crystallization event occurring at approximately 1090 °C corresponded to the transformation of amorphous silica into<i>β</i>-cristobalite, as confirmed by XRD. These findings provide insights into the structural and mechanical properties of EA skeleton, supporting the design of high-performance ceramic materials with enhanced mechanical properties for bioengineering applications.