WW Kolloquium: Prof. Dr. Derk Joester “On Structural and Compositional Gradients in Mineralized Tissues”

Prof. Dr. Derk Joester
Materials Science and Engineering Department,
Northwestern University, Evanston, IL, USA
“On Structural and Compositional Gradients in Mineralized Tissues”

Mineralized tissues are paradigmatic hierarchical materials that reap synergy from structural and compositional gradients at multiple length scales in ways that are challenging to reproduce by conventional means. My laboratory studies the formation, functional properties, and degradation of mineralized tissues. We use model systems ranging from single crystalline endoskeletal elements deposited by single cells to the formation of dental tissues that comprise nanocrystalline and amorphous minerals deposited in complex organic matrices. Applications include the development of bio-inspired materials, sequestration of 90Sr from nuclear waste, and improving prophylaxis and minimally invasive intervention in dental care.
Herein, I will focus on dental tissues that are optimized to withstand the forces of mastication and the challenging chemical environment of the oral cavity. For example, the radula teeth of the chiton are capped with a composite made of magnetite (Fe3O4) and a nano-fibrous chitin that allows them to excavate rock. Self-sharpening sea urchin teeth use magnesian calcite (CaCO3) at compositions very far from equilibrium to maintain an edge. Human tooth enamel is composed of hydroxylapatite (Ca5(PO4)3OH) crystallites, 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 but leaves our teeth vulnerable to erosive tooth wear and tooth decay (caries). I will discuss how chemical imaging using UV-laser pulsed atom probe tomography (APT), electron microscopy, and synchrotron X-ray techniques has provided deep new insights into the chemistry of nanoscale organic/inorganic interfaces, presence of amorphous intergranular phases, and complex dopant gradients that are integral to properties of teeth and their resistance to corrosion.[1-5] I will further report on development of correlative elemental imaging using X-ray diffraction at the mesoscale (here: 0.25-20 µm) that allows us to extend the field of view beyond what APT can deliver.[6] Finally, I will provide a progress report on our investigation of diffusive transport in enamel using APT.

[1] Gordon and Joester, Nature 2011, 469, 194-197. [2] Gordon, Tran, and Joester, ACS nano 2012, 6, 10667-10675. [3] Gordon, Cohen, MacRenaris, Pasteris, Seda, and Joester, Science 2015, 347, 746-750. [4] Gordon, Joester, Front Physiol 2015, 6. [5] DeRocher, Smeets, Goodge, Zachman, Balachandran, Stegbauer, Cohen, Gordon, Rondinelli, Kourkoutis, Joester, D. Nature 2020, 583, 66-71. [6] Free, DeRocher, Cooley, Xu, Stock, and Joester, Proc Natl Acad Sci USA 2022, 119, e2211285119.
This work was in part supported by: NIH-NIDCR R03 DE025303-01 and R01 DE025702-01; NSF DMR-1508399 and DMR-1539918; and DOE DE-AC02-06CH11357.

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