  Nature has engineered complex designs to achieve advanced properties and
functionalities through evolution, over millions of years. Many organisms have
adapted to their living environment producing extremely efficient materials and
structures exhibiting optimized mechanical, thermal, optical properties, which
current technology is often unable to reproduce. These properties are often
achieved using hierarchical structures spanning macro, meso, micro and
nanoscales, widely observed in many natural materials like wood, bone, spider
silk and sponges. Thus far, bioinspired approaches have been successful in
identifying optimized structures in terms of quasi-static mechanical
properties, such as strength, toughness, adhesion, but comparatively little
work has been done as far as dynamic ones are concerned (e.g. vibration
damping, noise insulation, sound amplification, etc.). In particular,
relatively limited knowledge currently exists on how hierarchical structure can
play a role in the optimization of natural structures, although concurrent
length scales no doubt allow to address multiple frequency ranges. Here, we
review the main work that has been done in the field of structural optimization
for dynamic mechanical properties, highlighting some common traits and
strategies in different biological systems. We also discuss the relevance to
bioinspired materials, in particular in the field of phononic crystals and
metamaterials, and the potential of exploiting natural designs for
technological applications.
