Porous morphology and graded materials endow hedgehog spines with impact resistance and structural stability

Hedgehog spines with evolved unique structures are studied on account of their remarkable mechanical efficiency. However, because of limitations of existing knowledge, it remains unclear how spines work as a material with a balance of stiffness and toughness. By combining qualitative three-dimensional (3D) structural characterization, material composition analysis, biomechanical analysis, and parametric simulations, the relationship between microstructural characteristic and multifunctional features of hedgehog spines is revealed here. The result shows that the fibers transform from the outer cortex to the interior cellular structures by the "T" section composed of the "L" section and a deltoid. The outer cortex, however, shows an arrangement of a layered fibrous structure. An inward change in Young's moduli is observed. In addition, these spines are featured with a sandwich structure that combines an inner porous core with an outer dense cortex. This feature confirms that the hedgehog spines are a kind of biological functionally graded fiber-reinforced composite. Biomimetic models based on the spine are then built, and the corresponding mechanical performance is tested. The results confirm that the internal cellular structure of the spine effectively improve impact resistance. Furthermore, the transverse diaphragm can prevent ellipticity, which may delay buckling. The longitudinal stiffeners also contribute to promote buckling resistance. The design strategies of the spine proposed here provide inspirations for designing T-joint composites. It also exhibits potential applications in low-density, impact and buckling resistance artificial composites. STATEMENT OF SIGNIFICANCE: The spines of a hedgehog are its protective armor that combines strength and toughness. The animal can not only withstand longitudinal and radial forces that are 1 × 10⁶∼ 3 × 10⁶ times the gravity generated by its own weight, but it can also survive unscathed by elastic buckling while dropping to the ground at a speed of up to 15 m/s. Here, we first demonstrate that hedgehog spines are biological graded fiber-reinforced structural composites and reveal their superior impact and buckling resistance mechanism through simulation analysis. Our results broaden the understanding of the relationship among morphology, materials, and function of hedgehog spines. It is anticipated that the survival strategies of hedgehog revealed here could provide inspirations for the development of synthetic composites with impact resistance and structural stability.