A novel biomimetic design inspired by nested cylindrical structures of spicules

Among the major groups of materials, some polymers and resins are limited in usage due to their brittleness. To date, we lack a comprehensive solution to overcome brittleness. Mimicking from biological structures made up of ceramics with excellent strength and flexibility can help us to find a solution to this problem. In this study, for the first time, we mimicked the structure of spicules in Euplectella aspergillum (EA) sponges and developed a novel structure to improve the mechanical properties of brittle rods. In the newly developed structure, cylinders with various diameters were printed by a 3D printer and then inserted into each other. The nested cylindrical structures (NCSs) with optimized mechanical properties had a cylinder wall thickness of 1.30 mm with a density of 1.27 ± 0.01 g/cm³ (approximately 8.6% less than that of solid rods (SRs)). The flexural strength, strain, modulus and toughness of SR were improved in the NCSs from 108.04 ± 11.30 MPa, 1.95 ± 0.20%, 3.98 ± 0.05 GPa and 1.42 ± 0.20 kJ/m³ to 168.45 ± 14.45 MPa, 4.10 ± 0.41%, 5.52 ± 0.05 GPa and 6.71 ± 0.80 kJ/m³, respectively. The NCSs showed a lower density as well as improved mechanical properties compared to SRs. According to the SEM observations, the dominant mechanisms on the toughening of NCSs with a cylinder wall thickness of 0.80 mm were crack branching, crack bridging, and crack deflection. However, for NCSs with a cylinder wall thickness of 1.00 and 1.30 mm the dominant mechanism was crack deflection. The results of this paper open a new horizon for designing new structures from brittle materials with higher strength and flexibility.