Compositional and architectural variation in urinary calculi from nucleus to periphery: an integrated IR spectroscopy, scanning electron microscopy and powder X-ray diffraction approach

A combination of IR spectroscopy, scanning electron microscopy (SEM) and powder X-ray diffraction has been used to analyze the compositional and architectural variation across the different parts (core, middle and outer layers) of five human urinary calculi (KS1–KS5) from eastern India. Rietveld quantitative phase analysis using X-ray powder diffraction revealed that the composition of the core regions in KS1–KS3 and KS5 is exclusively whewellite, whereas in KS4 it is a mixture of whewellite (84.5 wt%) and carbonated hydroxyapatite (15.5 wt%). While one of the renal stones, KS1, is composed of only whewellite in all three regions, a distinct variation in phase composition from the core towards the periphery has been observed in KS2–KS5. A drastic change in phase composition has been noted in KS5, with the major constituent phases in the core, middle and outer layers as whewellite (100.0 wt%), anhydrous uric acid (60.7 wt%) and carbonated hydroxyapatite (69.6 wt%), respectively. The crystallite size of whewellite in different parts of the kidney stones varies between 91 (1) and 167 (1) nm, while the corresponding sizes of the anhydrous uric acid in KS5 and carbonated hydroxyapatite in KS3 are 107 (1) and 18 (1)–20 (1) nm, respectively. SEM images of the kidney stones showed different levels of organization, resulting from an agglomeration of crystallites with diverse shapes and sizes.