Self-consistent field modelling of poly(lactic acid)–poly(ethylene glycol) particles

Self-consistent field (SCF) modelling studies on a series of varying molecular weight poly(lactic acid):poly(ethylene glycol) (PLA:PEG) particles (2:5–15:5 kDa) that form micelles in aqueous solutions have been performed using the formalism of Scheutjens and Fleer. The parameters were chosen to represent a central core made from collapsed hydrophobic PLA blocks, and PEG blocks, which form a corona layer extended into the solvent. These different phases have been confirmed in 1H and 13C NMR experiments. From the analysis of the relevant thermodynamic data of the series, particle radii and aggregation numbers varying from 12.6 to 24.9 nm and from 17 to 280, respectively, have been predicted, which agree well with those obtained experimentally. The actual thickness of the PEG corona is fairly constant at approximately 11 nm for the whole particle series indicating that the size of the PLA core has little effect on the thickness of the PEG corona layer. Another important consideration of these particles is the PEG density at the surface, which is related to the in vivo properties of these particles. The surface area available to each PEG block at the central PLA core has been obtained in order to compare the members of the particle series. It has been shown that the surface area available to each PEG block decreases and then increases throughout the PLA:PEG series.