Effects of charge density and thermal history on the morphologies of spontaneously formed unilamellar vesicles.

A phospholipid mixture consisting of dimyristoyl phosphatidylcholine (DMPC), dihexanoyl phosphatidylcholine (DHPC), and the negatively charged dimyristoyl phosphatidylglycerol (DMPG) lipid is found to spontaneously form uniform-size unilamellar vesicles (ULVs). Small angle neutron scattering (SANS) is used to examine ULV size as a function of net charge, dilution, and thermal history. It shows that ULVs only exist within a narrow window of charge densities, where larger size ULVs can be obtained at a lower charge density through slow temperature annealing. There is also a 6-fold change in the size of low polydispersity ULVs, confirming a previously proposed model for spontaneously forming ULVs [Nieh, M.-P. et al. Langmuir 2005, 21, 6656]. Finally, the stability of these ULVs was confirmed through a series of high temperature dilution experiments, further making the case that these nanoparticles can be used as carriers for drugs and contrast imaging agents.