(178j) Understanding Cholesterol Precipitation in Biomimetic Environments

Cholesterol plays an essential role in human physiology but it can also form key components 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 will show how a binary mixture of water and alcohol (i.e., biomimetic lipid surrogate) serves as an ideal medium to examine cholesterol crystallization in situ. Our preliminary findings reveal a two-step nucleation process involving the assembly of clusters using a combination of oblique illumination microscopy (OIM) and dynamic light scattering (DLS). We also found that these species are also directly involved in surface dissolution leading to unique surface dynamics that differ from any mechanisms reported in literature. 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. In this presentation, we will also discuss the results of in situ atomic force microscopy (AFM) and in situ microfluidics measurements, which were used to confirm mechanisms of surface growth involving classical nucleation from dislocations and layer-by-layer growth leading to macrosteps formation leading to growth cessation. Our findings reveal that growth occurs by incorporation of monomers into kinks by surface diffusion and we also posit that surface diffusion limitations lead to a unique self-inhibition mode of crystallization.