Abstract
Tooth biominerals are among the hardest biological materials. Optimized to withstand the forces of mastication, they are hierarchically structured, organic/inorganic nanocomposite materials. For example, the radula teeth of the chiton are capped with a composite made from magnetite (Fe3O4) and a nanofibrous chitin scaffold. These teeth are sufficiently hard that the chiton can abrade rocks during feeding. Human tooth enamel is composed of hydroxylapatite nanowires, thousands of which are bundled into rods that are organized in a three-dimensional weave; this provides great fracture resistance and a much enhanced fatigue life. It has long been known that the susceptibility of enamel to caries, i.e. acid corrosion, is greatly dependent on the presence of magnesium, carbonate, and fluoride ions. However, imaging the distribution of these impurities in enamel or the organic/inorganic interface in the chiton tooth has remained challenging.
I will discuss how UV-laser pulsed atom probe tomography (APT), in combination with correlative imaging and spectroscopy techniques, has given us remarkable new insights into the chemistry of organic/inorganic interfaces, grain boundaries, and amorphous intergranular phases that are integral to the mechanical properties of teeth and their resistance to corrosion.

Short Biography
Derk Joester is originally from Munich (Bavaria, Germany) and studied Chemistry in Tübingen. He travelled to the US on a Fulbright Scholarship to study Chemistry and Biochemistry, and then went on to get his Diploma in Organic Chemistry at ETH Zurich, Switzerland, in 1998. He received his Ph.D. for work carried out in organic, supra-molecular chemistry with Prof. François Diederich at ETH Zurich in 2003, and in the same year became a Postdoctoral Fellow at Weizmann Institute of Science in the lab of Prof. Lia Addadi in the Department of Structural Biology. From 2005-2007 he continued his research at the Weizmann Institute as a Minerva Fellow. In September 2007 he accepted a position at the Materials Science & Engineering Department at Northwestern University, Evanston, Illinois. In 2013, he was promoted to Associate Professor. His research interests include biological mechanisms of crystal growth, the role of organic/inorganic interfaces and confinement in phase transformations, metastable precursor phases, and the structure and properties biomineral-organic composites with hierarchical architectures.