Figure 4.
In analogy to proteins, biominerals use the same concept of creating building blocks from building blocks. In the protein world, the building blocks of the different hierarchy levels (H0 to HN) are distinct in their nature: amino acids form secondary structure elements (α-helices, β-sheets, etc.) which then form a super structure (e.g. a coiled-coil) and so forth. In biominerals, it seems that a reoccurring, eternal design motif (represented by using Lego™ blocks) is used throughout the hierarchy levels: inorganic building block with a high surface-to-volume ratio, coated with an energy-dissipative interelemental glue of organic nature. Depending on the requirement (e.g. the external threat, damage, or the material property under investigation), the material's response may be fully understood by neglecting subjacent levels, e.g. starting from H0′, taking this as the irreducible and thus fundamental element. Inspired from [8].