Imaging Interfaces and Interphases in Mineralized Tissues

Mineralized tissues are sophisticated materials with properties that include high toughness at low weight, outstanding fatigue life, self-repair capabilities, and sustainable synthesis. Often hierarchically structured, grain and interphase boundaries play an important role in the biosynthesis and final functional properties of mineralized tissues. However, the complex structure and phase composition, often with characteristic features at the nanoscale, the low atomic number of many physiologically relevant elements, and sensitivity to electron and X-ray beams creates significant challenges to the characterization of these biological materials.<br/><br/>I will discuss how UV-laser pulsed atom probe tomography (APT) has provided us with deep insights into compositional gradients at organic-organic interfaces in invertebrate teeth and bone-type tissues, helped us identify the role of an amorphous intergranular phase that acts as a cement in rodent enamel, and discover nanoscale gradients in hydroxylapatite crystallites in vertebrate tooth enamel.[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 characterization of a highly unusual biomineral, celestine (SrSO₄), that is found in single crystalline endoskeletal spicules in Acantharea, a class of marine zooplankton. This investigation is motivated by the high level of biological control over single-crystal growth evident in different Acantharea species, and because understanding how Acantharea selectively sequester Sr²⁺ over chemically similar ions present in seawater, is of interest for example for removal of ⁹⁰Sr from nuclear waste.<br/> <br/>[1] Gordon and Joester, <i>Nature </i><b>2011</b>, <i>469</i>, 194-197. [2] Gordon, Tran, and Joester, <i>ACS nano </i><b>2012</b>, <i>6</i>, 10667-10675. [3] Gordon, Cohen, MacRenaris, Pasteris, Seda, and Joester, <i>Science </i><b>2015</b>, <i>347</i>, 746-750. [4] Gordon, Joester, <i>Front Physiol </i><b>2015</b>, <i>6</i>. [5] DeRocher, Smeets, Goodge, Zachman, Balachandran, Stegbauer, Cohen, Gordon, Rondinelli, Kourkoutis, Joester, D. <i>Nature</i> <b>2020</b>, <i>583</i>, 66-71. [6] Free, DeRocher, Cooley, Xu, Stock, and Joester, <i>Proc Natl Acad Sci USA </i><b>2022</b>, <i>119</i>, e2211285119.