Biominerals are widely exploited to harden or stiffen tissues in living organisms, with calcium-, silicon-, and iron-based minerals being most common. In notable contrast, the jaws of the marine bloodworm Glycera dibranchiata contain the copper-based biomineral atacamite [Cu ₂ (OH) ₃ Cl]. Polycrystalline fibers are oriented with the outer contour of the jaw. Using nanoindentation, we show that the mineral has a structural role and enhances hardness and stiffness. Despite the low degree of mineralization, bloodworm jaws exhibit an extraordinary resistance to abrasion, significantly exceeding that of vertebrate dentin and approaching that of tooth enamel.

Wood is a natural fibre composite with a hierarchical cellular structure of a specific strength and a specific modulus of elasticity that can be compared with those of other common construction materials. Each wood cell is typically built of cellulose fibrils spiralling around the macroscopic fibre direction. While it is natural to assume a relation between the microfibril angle (MFA) and the mechanical properties, a good correlation has up to now only been established for single fibres, where a larger extensibility was found for fibres with larger MFA. In the present paper, we show for the first time that this relation even exists for thin (200 μm) sections of wood, which provides strong evidence for the fact that the MFA optimizes the extensibility of wood. In a combination of tensile tests with structural investigations by small angle X-ray scattering on the same sample of Picea abies, we found a remarkable increase in maximum strain with increasing MFA, and also a change in the elastic moduli.

Higher animals typically rely on calcification to harden certain tissues such as bones and teeth. Some notable exceptions can be found in invertebrates: The fangs, teeth, and mandibles of diverse arthropod species have been reported to contain high levels of zinc. Considerable quantities of zinc also occur in the jaws of the marine polychaete worm Nereis sp. High copper levels in the polychaete worm Glycera dibranchiata recently were attributed to a copper-based biomineral reinforcing the jaws. In the present article, we attempt to unravel the role of zinc in Nereis limbata jaws, using a combination of position-resolved state-of-the-art techniques. It is shown that the local hardness and stiffness of the jaws correlate with the local zinc concentration, pointing toward a structural role for zinc. Zinc always is detected in tight correlation with chlorine, suggesting the presence of a zinc–chlorine compound. No crystalline inorganic phase was found, however, and results from x-ray absorption spectroscopy further exclude the presence of simple inorganic zinc–chlorine compounds in amorphous form. The correlation of local histidine levels in the protein matrix and zinc concentration leads us to hypothesize a direct coordination of zinc and chlorine to the protein. A comparison of the role of the transition metals zinc and copper in the jaws of two polychaete worm species Nereis and Glycera , respectively, is presented.