Diatom frustule-inspired elastic metamaterials

Although a universally accepted definition of elastic metamaterials does not exist yet, the latter are often associated to man-made or artificially engineered media possessing properties typically not available in Nature. Pioneering studies have recently demonstrated that complex structural organizations, often arranged in a periodic and/or gradient manner and spanning multiple length scales, typically found in many biological systems, exhibit extraordinary absorption/reflection functionalities enhanced by local resonances or Bragg scattering mechanisms. This has opened the road to new designs of bio-inspired metamaterial. In this context, here we investigate the elastic dynamic response of diatom frustules, i.e., the exoskeleton structures of photosynthetic algae ubiquitously present throughout the planet in water environments. Firstly, we analyse and record their structural arrangement in nano- and micro- scales by using the Scanning Electro Microscopy (SEM) and the optical profilometer. The results of the analysis are transferred to the metamaterial design. Secondly, through numerical models, we show the possibility of certain frustule-inspired geometries to behave as frequency selective elastic filters thanks to the presence of elastic bandgaps. The work herein contributes to the perspective of elastic metamaterials inspired by Nature.