Tunable Energy Absorption in Bioinspired Materials Designed for Additive Manufacturing

Diatoms are the most widespread organisms in our planet’s aquatic environments and among the most ecologically important. Indeed, the tens of thousands of existing species of these microalgae produce about half of the oxygen we breathe and are an extraordinary example of how Nature is capable of cyclically adapting biological systems to the natural environment by playing with the universality-diversity dualism. In diatoms, in particular, this binomial is determined by the multiscale architecture of their biosiliceous exoskeleton known as the “frustule”. This biological material, in addition to being a marvelous and sophisticated physical barrier against predators, through its hierarchical porous structure allows diatoms to acquire nutrients through filtration, exploit buoyancy phenomena for photosynthesis processes, and thermally regulate the organism. Given the amazing multifunctionality of the frustule, diatoms are still widely studied for applications in filtration, drug delivery, biosensing, energy harvesting, and scaffolding. Yet, little is known regarding their mechanical properties. To extend the knowledge of the present relationship between the morphology of diatom frustules and their structural performance, in this work we focused on the mechanical analysis of the frustule of the diatom Coscinodiscus sp. Starting from the analysis of the multilayer structure that characterizes the microscale, we built biomimetic models on a macroscopic scale using CAD tools and studied their deformational behavior, both through numerical finite element simulations and through experimental tests performed on samples fabricated through additive manufacturing. In particular, we focused on the effect produced by variation in the morphological details that distinguish the natural sandwich-like structure of the frustule on its energy absorption properties. Through predictive techniques, we then researched the optimal topology and analyzed the potential benefits of using bioinspired design for the architected materials. Nature’s design principles used to make biological materials and, in particular, the use of functional gradients and structural heterogeneity are a formidable source of ideas for increasing the efficiency and performance of man-made materials, and this research is evidence of that. To reinforce this, as a possible application, we propose in addition a new bioinspired prototype protective helmet designed for micromobility and outdoor activities that combines lightweight and the energy-absorbing capacity from impacts with breathability, waterproofing, and aesthetics.