Precipitation in liposomes as a model for intracellular biomineralization

Liposomes present a versatile platform to model intracellular, biologically controlled mineralization. Perhaps, most importantly, precipitation in the confinement of liposomes excludes heterogeneous nucleators that facilitate formation of the thermodynamically most stable crystalline phase in bulk. This provides access to metastable amorphous precursors even in the absence of other additives that interact strongly with the mineral and is fundamental to the capability of cells to prevent spurious nucleation and to select a specific polymorph. Herein, we summarize methods to prepare liposomes from the nanometer to micron length scale and review strategies to carry out precipitation reactions of iron oxide, calcium carbonate, and calcium phosphate in the confinement of such liposomes. In addition, we discuss methods to characterize the morphology, structure, and growth kinetics of crystalline and amorphous precipitates, with particular emphasis on in situ characterization approaches.