The multilayer design principle of multifunctional artificial shells

Living organisms employ a key strategy to construct resilient load-bearing structures: the strategic layering of anisotropic elements. Natural biomineralized tissues showcase a remarkable attribute—an exact alignment of multiple building units, a quality notably absent in contemporary biomimetic reproductions. We demonstrate the fabrication of artificial shells by integrating vertically aligned TiO2 nanorods into a polymer matrix atop clay multilayers. This approach combines chemical synthesis with molecular assembly to mimic the bilayer structure of mollusk shells, which consists of polygonal prismatic units on a brick-and-mortar architecture. Our study reveals a critical design principle for artificial shells through a combination of nanoindentation and finite element analysis. This design minimizes stress concentration factors at the interface and enhances penetration resistance, mainly attributed to the properties of the bottom layer. In comparing our artificial shells with their natural counterparts, we uncover additional design principles, such as hierarchical architecture and microscale prism size. These artificial shells possess the intriguing ability to partially self-heal due to a dynamic hydrogen bonding network. Furthermore, they can serve as humidity-sensitive actuators, with bending direction controlled by the aspect ratios of clay nanosheets. Our work offers valuable insights for the rational design of multifunctional, multilayer materials with enhanced impact resistance.