High-surface-area nanoparticles often cluster, with unknown effects on their cellular uptake and environmental impact. In the presence of vesicles or cell membranes, lipid adsorption can occur on the nanoparticles, resulting in the formation of supported lipid bilayers (SLBs), which tend to resist cellular uptake. When the amount of lipid available is in excess compared with that required to form a single-SLB, large aggregates of SLBs enclosed by a close-fitting lipid bilayer sheath are shown to form. The proposed mechanism for this process is one where small unilamellar vesicles (SUVs) adsorb to aggregates of SLBs just above the gel-to-liquid phase transition temperature, Tm, of the lipids (as observed by dynamic light scattering), and then fuse with each other (rather than to the underlying SLBs) upon cooling below Tm. The sacks of SLB nanoparticles that are formed are encapsulated by the contiguous close-fitting lipid sheath, and precipitate below Tm, due to reduced hydration repulsion and the absence of undulation/protrusion forces for the lipids attached to the solid support. The single-SLBs can be released above Tm, where these forces are restored by the free lipid vesicles. This mechanism may be useful for encapsulation/release of drugs/DNA, and has implications for the toxic effects of nanoparticles, which may be mitigated by lipid sequestration.
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