Use of Viscoelastic Measurements for Investigating Interparticle Interactions in Dispersions of Micellar-like Poly(lactic acid)−Poly(ethylene glycol) Nanoparticles

Abstract

A series of poly(lactic acid)-poly(ethylene oxide) (PLA-PEG) AB block copolymers have been synthesized and used to produce aqueous dispersions of micellar-like nanoparticles. The hydrodynamic radius of the PLA core plus the stabilizing 5 kDa PEG layer, as determined by photon correlation spectroscopy, increased with the molecular weight of the PLA block. PLA-PEG particles have possible application as drug carriers for targeted drug delivery. In addition to particle size, the layer thickness and mobility of the hydrated PEG chains will be important in determining the particle's ability to avoid uptake by the defense system of the body, the phagocytic cells of the reticuloendothelial system. Viscoelastic measurements were used to investigate interparticle interactions in concentrated dispersions of the PLA-PEG nanoparticles. This approach has not previously been used to study how the interactions in dispersions of micellar-like assemblies depend on the copolymer geometry. When the volume fraction of the dispersions, φcore, was increased, the storage modulus, G′, became greater than the loss modulus, G′′, indicating steric interaction between the PEG chains. At higher φcore values, compression of the grafted polymer chains was observed. The critical volume fraction at which overlap of the PEG chains commences, φcore crit (i.e., G′ ) G′′), was used in conjunction with the overall hydrodynamic radius to determine the grafted PEG chain layer thickness. Micellar-like nanoparticles assembled from a PLA-PEG copolymer with a 5 kDa PEG block and a relatively low molecular weight 3 kDa PLA chain had an appreciable steric layer thickness of 6.3 nm. Hence, interparticle interactions in the concentrated dispersion were "soft" in nature as a result of the long-range interactions, as shown by the weak scaling dependence of the storage modulus on the volume fraction. The layer became more extended as the molecular weight of the PLA block was increased from 3 to 6 kDa, and as a consequence the PEG chains became less compressible. By using this method to characterize the PEG layer, it should be possible to rationalize the in vivo performance of the PLA-PEG nanoparticles and therefore aid the design of particulate drug carriers.

Hollow Block Copolymer Nanoparticles through a Spontaneous One-step Structural Reorganization

“…In order to test this theory, poly(ethylene oxide) [P(EO)] was utilized as an alternative, non hydrogen-bond donor corona block. Solid spherical micelles with number average R h of 8.0 nm (as measured by DLS) were obtained from commercially available P(EO) 5k - b -P( d , l -LA) 4k as previously demonstrated. , Then, these particles were dried on GO TEM grids using the same slow evaporation preparation used with the P(AA)- b -P(LA). The resulting nonstained TEM images revealed a uniform electron density across the surface of the particles, with the complete absence of hollow structures, indicating that no structural reconstruction had occurred (Figure S21, Supporting Information).…”

Indomethacin solubilization induced shape transition in CnE7 () nonionic micelles

“…The design of long-circulating drug carriers has focused on surface modifications to change the quality and quantity of the plasma components adsorbed because the phagocytosis is mediated by the adsorption of certain blood components [5][6][7]. Particles stabilized with polyethylene oxide are known to avoid phagocytosis and are effective in prolonging the drug circulation time in biological systems [6,8].…”

Stability of Concentrated Olive Oil‐in‐water Emulsion

“…Since the G' is influenced by the strength of droplet-droplet attraction, it implied that the emulsion droplets strongly interacted. 27 As observed in the micrographs (Figure 3), the interdroplet distances were extremely small compared to the radius of the droplets. Thus, translational motion of the droplets is limited and this phenomenon was concluded as 'hard sphere' system, 24,28 which is typically solid like behavior (Figure 8).…”

“…The observed Tan ∂ values ranged from 0.30 to 0.18, which characterized the emulsion as solid like. 24,27,29 From the Figures 7 and 8, the results also show that the dynamic properties of the emulsion were independent of the storage time. This implied that the emulsion was very stable.…”

“…24,26 The G' of the emulsion shows no significant changes within the 30 d of storage time (Figure 7) due to the ability to retain the structural integrity of the emulsion. G', a measurement of the energy stored elastically during a cycle, 24,26,27 was increased with frequency and five times greater than the G''. Since the G' is influenced by the strength of droplet-droplet attraction, it implied that the emulsion droplets strongly interacted.…”