Formation of cholesterol crystals at a mucin coated substrate

Purpose. High-resolution, tapping-mode atomic force microscopy (AFM) was used to monitor the early stage of the formation of cholesterol crystals under simulated conditions of the gallbladder environment. Methods. AFM images of phosphatidylcholine/cholesterol vesicles were obtained using a mucin-coated mica substrate. Results. The vesicles appeared flattened with diameters from 100 to 300 nm and heights that varied from 10 to 100 nm. Phosphatidylcholine/ cholesterol vesicles were mixed with bile salt solutions to yield supersaturated (with respect to cholesterol) dispersions, which were then placed onto mica, silanized mica, and mucin-covered mica substrates. After equilibration, sub-micron sized, plate-like structures were observed at the mica and mucin covered surface, but none were seen at the silanized surface. The morphology was characterized as it pertains to the relative growth rates of the crystal faces. Conclusion. The comparison of these results with literature reports of cholesterol crystals grown in solution suggests that the physical chemical properties of the surface have an important influence in determining the nucleation and subsequent crystal growth of cholesterol.