Effect of poly(ethylene glycol) stearate on the phase behavior of monocaprate/Tween80/water system and characterization of poly(ethylene glycol) stearate-modified solid lipid nanoparticles

In the present contribution, surface-modified SLNs have been prepared from precipitation in an oil-in-water microemulsion, using monocaprate (MC) as solid matrix, polyethylene glycol sorbitan monooleate (Tween80) as emulsifier and poly(ethylene glycol) stearate (PEG-S) as surface modifier. The aim of present work was to evaluate the effect of PEG-S on the phase behavior of MC/Tween80/H2O system as well as on the properties of surface-modified SLNs. Three different PEG-Ss: PEG8-S, PEG40-S and PEG100-S with varying PEG chain length were used to modify SLN. First, the effect of PEG-S on pseudo-ternary phase showed that the presence of PEG-S extended the areas of liquid crystal and microemulsion in the phase diagram. Meanwhile, with increasing the PEG chain length, liquid crystal and microemulsion areas extended to the water corner. In addition, the morphology and microstructure of PEG-S-modified SLN were investigated. The pictures of transmission electron microscope (TEM) and environmental scanning electron microscopy (ESEM) showed that the modified SLNs to be spherical particles, and the average diameters measured by dynamic light scattering (DLS) were between ca. 71 nm and ca. 140 nm. The crystallographic properties of them were characterized by X-ray diffraction (XRD). It was found that PEG-S did not exist in crystallline state in the SLN, both surface-modified and non-modified SLN existed in the amorphous state. Further more, zeta potential analysis and the Fourier transform infrared spectrum (FTIR) were carried out, and the results revealed that conformations of PEG-S on the surface of SLN were different when changing the concentration and the EO chain length of PEG-S both in solid state and liquid state.