ADVANCED MATERIALS & PROCESSES | APRIL 2024 55 interactions, efficient crack arrest mechanisms, and localized hardening responses, facilitating energy dissipation and impeding localized damage. By tailoring geometric parameters and building block dimensions, these hierarchical architectural configurations can be systematically adjusted to significantly augment composite toughness. Applying these lessons to engineered composites can significantly improve biomimetic composite toughness, and these hierarchical designs may be modified in terms of geometrical factors and building block size. Even with the presence of inner channels and pore canals, these natural architectures are inherently resistant to failure. Examples can be found in human blood vessels arranged in parallel within the cortical bone, surrounded by concentric tissue, and reinforced with a cement layer at the edges. Tooth dentin exhibits parallel channels covered by layers of mineralized peritubular dentin and intertubular dentin. Respiratory adaptations in certain species such as striped dolphins and leatherback sea turtles employ erectile tissue and uncalcified cartilage, respectively, to protect against damage under high pressure. Other examples can be found in the dactyl club of the mantis shrimp and the exoskeletons of some beetles. These structures contain both hard, brittle material and channels that weaken the material by acting as stress concentrators. Despite this, they possess remarkable mechanical properties and still satisfy their fluid transport needs. INNOVATIVE APPROACH AT PURDUE Researchers at Purdue University are working on unlocking the secrets of nature’s design to create robust and lightweight materials that resist stress without undergoing plastic deformation and have the capacity to absorb impact energy and react to stimulus to adapt, change shape, and do work. Taking inspiration from natural patterns such as the honeycomb arrangement of flattened spherical structures in human bones and the layering of cardboard, the team is exploring the intricate mechanics of materials. By collaborating with industry leaders in manufacturing, they are leveraging these patterns to engineer architected materials capable of absorbing energy and returning to their original state. In civil engineering, the conventional approach is to avoid buckling failures. However, deliberately integrating controlled buckling into a structure’s design allows it to deform under applied forces and rebound to its original shape. Architected materials are engineered to undergo controlled buckling at specific points, transferring forces to other components and maintaining structural integrity. These designs have broad applications, from earthquake-resistant buildings to impact-resistant helmets. The Purdue team is exploring designs using optical, magnetic, or thermal properties for biomedical applications, envisioning materials that can fold to fit inside a catheter and expand when heated. Fig. 3 — Various features of architected materials along with sample images both from and inspired by nature. 9 FEATURE
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