Phospholipid-enveloped biodegradable polymer microparticles and nanoparticles synthesized by an emulsion/solvent evaporation process were characterized by confocal and cryoelectron microscopies to show that the lipid envelope exhibits two-dimensional fluidity and can be configured into 'shell', 'onion', or 'flower' nanostructures, depending on the quantity and composition of lipids employed in the synthesis.