Mapping lattice spacing and composition in biological materials by means of microbeam X-ray diffraction

Abstract

Many biological materials and in particular biomineralized tissues exhibit structural and compositional gradients at several length scales. Nanostructural features varying at the micrometer scale can be imaged by employing synchrotron radiation based small- and wide-angle X-ray scattering combined with microbeam scanning. In particular, the lattice distortions caused by a substituted atoms within a crystal structure can be mapped by evaluating the corresponding shifts of Bragg reflections. As we demonstrate here by reviewing three examples of mineralized biological tissues, this approach delivers valuable complementary information to chemical imaging (e.g., X-ray fluorescence imaging). Specifically, we show that strontium is incorporated in the hydroxyapatite crystal structure of human bone after osteoporosis treatment with Sr ranelate. Moreover, we discuss how local magnesium gradients within two different calcite phases in the tip of the sea urchin tooth may relate to the excellent mechanical properties and the self sharpening ability of this exceptional grinding tool. Finally, we show how this method allows drawing conclusions about the stability of the amorphous calcium carbonate in the cuticle of the American Lobster by determining the magnesium concentration after crystallization induced by an in situ heat treatment. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.