Nature uses chemistry to build strong, resilient, tough materials tailor made for the job at hand. The carnivorous bloodworm, for instance, needs a hard, wear-resistant, flexible jaw to knaw through carapaces and burrow through sediment. It's recipe includes four substances: proteins, melanin pigment, copper ions, and atacamite (a mineralized form of copper) arranged in four layers in precise patterns and thicknesses. Copper ions facilitate a tight network between proteins and pigment in the thin outermost layer as well as in the third layer confering hardness and wear resistance. Sandwiched between these two is a layer reinforced with atacamite fibers thought to confer flexibility to the entire jaw. The innermost layer contains ony trace amounts of copper.Edit Summary
"Glycera jaw is a biocomposite primarily composed of three components: proteins (~50 wt%), eumelanin pigment (~40 wt%) and copper (10%) in both mineralized (Cu2(OH)3Cl, atacamite) and unmineralized forms...Copper distribution is highly inhomogeneous and enriched towards the edges and tip...the jaw is comprised of four distinct microstructural layers: (i) In the outer layer, 3–5 μm thick, Cu ions are present in non-mineralized form. (ii) Within the second domain, roughly 5–15 μm thick, one finds the mineralized atacamite fibres; (iii) The third domain is chemically similar to the outer layer, but is significantly thicker (10–20 μm); (iv) At a depth of 30–40 μm one reaches the 'bulk' of the jaw, lacking significant Cu deposits." (Rubin et al. 2010:92)
"Together, the presence of the melanin scaffold, the high histidine content and the presence of copper ions form a tightly constructed network in which Cu can mediate strong coordination with imidazole ligands on the one side and the dihydroxyindoles of the melanin scaffold on the other...providing chemical and structural stability" (Rubin et al. 2010:93)
"[T]he highest wear performance is associated with regions enriched with non-mineralized Cu ions directly on the jaw surface. Remarkably, the level of hardness and modulus attained in this domain surpass those achieved on highly cross-linked synthetic polymer. The atacamite-rich domain, on the other hand, exhibits lower wear and scratch resistance, suggesting that they might serve a different function. One role hypothesized is that the atacamite fibres provide increased bending stiffness...While each layer may be considered a composite of melanin, protein and metal, the jaw as a whole can be considered a stratified composite encompassing a wear-resistant outer shell, a reinforced, rod-like interior and a second wear-resistant inner shell. These intricacies in construction are undoubtedly necessary in achieving the robust whole-jaw properties that are required by Glycera for their niche-specific survival activities." (Rubin et al. 2010:95)
See the online images from Rubin et al (2010).