Three-dimensional Periodic and Fractal Precipitation in Metal Ion-Deoxycholate System: A Model for Gallstone Formation

It was recently suggested that the periodic and fractal precipitation of calcium salts and proteins in cholesterol gallstonesis closely related to the process of stone formation. The present study is to mimic the process of gallstone growth in vitro. We demonstrate for the first time that a three-dimensional structure of periodic rings (Liesegang ring) and/or fractal patterns can be produced by metal ion and deoxycholate precipitation, which are similar to gallstones. Precipitation in a periodic pattern occurs more often than in a fractal structure. Using X-ray diffraction, polarized light microscope, Fourier transform-infrared (FT-IR), and extended X-ray absorption fine structure (EXAFS), we studied the pattern formation mechanisms of both types of structures. The results indicate that the rate of nucleation in the crystal growth is a crucial element to affect the pattern formation. The pattern selection between periodic and fractal type depends on the crystal growth speed and the rate of nucleation.