Control of the stability and structure of liposomes by means of nanoparticles

Abstract

The interaction of bilayer vesicles with hard nanoparticles is of great relevance to the field of nanotechnology, e.g., its impact on health and safety matters, and also as vesicles are important as delivery vehicles. In this work we describe hybrid systems composed of zwitterionic phospholipid vesicles (DPPC), which are below the phase transition temperature, and added silica nanoparticles (SiNPs) of much smaller size. The initial DPPC unilamellar vesicles, obtained by extrusion, are rather unstable and age but the rate of ageing can be controlled over a large time range by the amount of added SiNPs. For low addition they become destabilized whereas larger amounts of SiNPs enhance the stability largely as confirmed by dynamic light scattering (DLS). z-Potential and DSC measurements confirm the binding of the SiNPs onto the phospholipid vesicles, which stabilizes the vesicles against flocculation by rendering the z-potential more negative. This effect appears above a specific SiNP concentration, and is the result of the adsorption of the negatively charged nanoparticles onto the outer surface of the liposome leading to decorated vesicles as proven by cryogenic transmission electron microscopy (cryo-TEM). Small amounts of surface-adsorbed SiNPs initially lead to a bridging of vesicles thereby enhancing flocculation, while higher amounts render the vesicles much more negatively charged and thereby longtime stable. This stability has an optimum at neutral pH and for low ionic strength. Thus we show that the addition of the SiNPs is a versatile way to control the stability of gel-state phospholipid vesicles and also to modulate their surface structure in a systematic fashion. This is not only of importance for understanding the fundamental interaction between SiNPs and bilayer vesicles, but also with respect to using silica particles as formulation aids for phospholipid dispersions.

Internalization of Silica Nanoparticles into Fluid Liposomes: Formation of Interesting Hybrid Colloids

“…The instability observed for low SiNP content results from the presence of just a few adsorbed particles that introduce an attractive interaction, thereby bridging neighboring liposomes. [10,12] In contrast, the higher stability found for larger NP concentrations was attributed to the adsorption of a sufficiently high amount of charged NPs onto the vesicle surface, thereby introducing repulsive interactions between those SiNP-decorated vesicles.…”

“…These processes occur faster for lower [NP]/[vesicle] ratios. Apparently, in the case of higher concentrations of SiNPs, the larger amounts of adsorbed SiNPs stabilize the vesicles electrostatically, [10] thereby delaying the process of fusion responsible for the increase in R h . In contrast, the pure DOPC dispersion (b = 0) shows almost no changes during the observation period of four weeks since the fluid vesicles are stabilized by undulation forces.…”

“…[13] These results are similar to observations reported for comparable mixed systems containing gel-state bilayer vesicles (dipalmitoylphosphatidylcholine, DPPC, at room temperature). [10] In that case, the rigidity of the gel membrane, having a bending modulus (k) around 120 10 À20 J (about 300 kT), [11] prevents SiNP transport through the bilayers. The instability observed for low SiNP content results from the presence of just a few adsorbed particles that introduce an attractive interaction, thereby bridging neighboring liposomes.…”

Self-healable and reversible liposome leakage by citrate-capped gold nanoparticles: probing the initial adsorption/desorption induced lipid phase transition

“…We did not observe local bending of the lipid membrane as in the case of adsorption of small silica NPs. 16,40 This indicates that the interaction force might be different for AuNPs and small silica NPs when interacting with PC lipids. In addition, AuNPs are not uniformly distributed on liposome surface.…”

Liquid Foams, New Approaches in Raw Materials, Sustainability and Product Safety, Forum for Innovations

“…When bringing the solution below the main transition temperature of the membrane, the authors managed to "freeze" the vesicle system and thus achieved the preparation of stable decorated vesicle structures (as evidenced by CryoTEM) (Figure 7) [8].…”