Figure 6

Structure and chemical composition of intratubular (a) and interstitial (b) minerals in the medullo-papillary complex (MPC). Images on the left (a) illustrate intratubular mineral in the proximal regions of the MPC at lower magnification (TEM, bright field) and via a selected area electron diffraction (SAED a) pattern (bottom) of the mineral aggregates outlined in green in (a). High-angle annular dark-field (HAADF) scanning TEM (STEM) illustrates a heterogeneous distribution of lower and higher atomic weight elements in regions 1 and 2. Elemental mapping by STEM X-ray energy dispersive spectrometry (XEDS) of regions labeled “1” and “2” in (HAADF a) identify calcium (Ca), phosphorus (P), oxygen (O), magnesium (Mg), and possibly zinc (Zn) (right column and bottom row). The results of quantitative analysis of the elemental maps are shown in Table S1. In contrast, interstitial minerals known as nanostones or calcified nanoparticles (CNPs) are imaged in distal regions of the MPC (TEM, bright field, bi) with the corresponding SAED pattern (SAED bi) also shown. Interstitial mineralization was identified with collagen fibrils (bii1) and nanostones (bii2). Respective SAED patterns show diffraction spots and indicate crystallites oriented along the collagen fibril (SAED bii1) and the presence of crystallites with no preferred orientation associated with nanostones (SAED bii2). A HAADF view of the interstitial minerals is shown in the large image below. Elemental mapping by XEDS of the highlighted region identified (Ca, P, O, Mg) and possibly Zn. Quantification results of elements in sub-regions marked 1 and 2 are shown in Table S1.