Metal-Halogen Biomaterials and Wear Resistance

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

Title: Metal-Halogen Biomaterials and Wear resistance PI: Robert Schofield, University of Oregon Eugene The jaws, leg claws, stings and other "tools" of a many arthropods and other invertebrates, contain extraordinarily high amounts of heavy metals, such as zinc and manganese, and halogens such as bromine and chlorine. Although the concentrations reach 25% of dry mass, unlike calcified human teeth, invertebrate tissue is not filled with the biomineral. Instead, metal-halogen biomaterials appear to be a distinctly different system that is more widely employed among small organisms. Very little is known about these metal-halogen biomaterials, though their main counterpart in larger organisms, calcification, is thought to be of such importance that its advent made possible the evolution of organisms such as mollusks and vertebrates. In their previous NSF-funded project, the PIs published the first comprehensive picture of the development and microscopic structure of Zn-enriched 'tools', showing that Zn was deposited very late in exoskeleton development, and that Zn-rich tissue contained a unique network of canals, through which Zn was deposited. The PIs test the hypothesis that metal-halogen tissues represent a distinct class of biomaterials, differing substantially from biomineralized tissues. Further they suggest that because of similarities in the metal-halogen tissues of distantly related organisms, that this system is likely to have evolved very early, before the evolution of insects and chelicerates. The PIs have shown that the hardness of the mandibular teeth of leaf cutting ants increases by three times as Zn is incorporated during early adult life and suggested that this Zn-correlated hardness increase is responsible for the differences in leaf-processing behavior between young and older adults. In the present study, 4 hypotheses will be tested focusing on two areas; 1) the chemical form and mechanism by which Zn alters mechanical properties, and, 2) a comparison of the mechanical property in invertebrates with more familiar biomineralized tissue. It is expected that, for small organisms, metal-halogen biomaterials will impart a more advantageous balance of hardness and wear resistance than will calcification. This research will improve our basic understanding of inorganic biochemistry related to wear resistance, which may have been important to the evolution, behavior and life span of invertebrates. In addition, this research may lead to the development of new materials that mimic those designed by nature.