(150g) Unique Nonclassical Pathways of Cholesterol Crystallization in Biomimetic Media

Cholesterol plays an essential role in human physiology but is also a key component of pathological diseases such as heart plaque (atherosclerosis) and gallstones. Despite its relevance to worldwide healthcare problems, few studies have examined fundamental mechanisms of cholesterol crystallization. Here, we show how a binary mixture of water and ethanol (i.e., lipid surrogate) serves as an ideal medium to examine cholesterol crystallization in situ. Our preliminary findings reveal the impact of biomimetic ethanol-water mixtures on cholesterol monohydrate crystallization. We used a combination of oblique illumination microscopy (OIM) and dynamic light scattering (DLS) to prove that cholesterol nucleation involves a two-step process involving the assembly of clusters, which are present in both undersaturated and supersaturated media. These species are also directly involved in surface growth. Scattering measurements confirmed that cluster size is a function of temperature and water content, but is independent of cholesterol concentration. DLS data also revealed that solvent composition has a notable impact on the induction time and rate of crystal growth. We will also discuss the results of in situ atomic force microscopy measurements, which were used to confirm surface growth involves a combination of a classical layer-by-layer mechanism governed by diffusion-limited monomer incorporation and a nonclassical pathway involving cluster attachment. The presence of these clusters also has a unique impact on the dynamics of layer propagation during cholesterol monohydrate crystal surface growth that differs from any crystal growth mechanisms reported in literature.