Surface chemistry of phospholipid vesicles relevant to their aggregation and fusion

A general description of those forces that are important in the stability of the lipid bilayer is presented. The analysis focuses on those that may change under conditions in which aggregation or fusion of vesicles or exchange of their molecules may occur. It is that class of membrane forces that is most likely to play a role in the process(es) that leads to the formation of cholesterol crystals in bile, which eventually grow into gallstones. A specific, hypothetical mechanism for cholesterol crystal nucleation based on vesicle fusion is also given. This mechanism is consistent with the principles of surface chemistry outlined.