Preparation of solid lipid nanoparticles in co-flowing microchannels

This work presents an effective and new method for producing solid lipid nanoparticles (SLNs) with small sizes (mean diameter less than 250 nm) and relatively narrow size distribution (polydispersity less than 0.26). The preparation process was conducted in a co-flowing microchannel assembled with inner and outer capillaries. A lipid-solvent phase was injected into the inner capillary, while an aqueous phase with surfactant was injected into the outer capillary. The solvent in the lipid-solvent phase diffused into the aqueous phase when the two phases meet in the outer capillary, resulting in the local supersaturation of lipid and finally the formation of SLNs. Softisan 100 (triglyceride mixture of fatty acids with chain lengths of C10 to C18) was used as the test lipid and SLNs were prepared in the present microchannel system under various operation conditions. The mean diameter and the size distribution of the SLNs obtained were measured by dynamic light scattering (DLS) method and the particle morphology was examined by transmission electron microscopy (TEM). The results showed that the diameter of the SLNs decreased with the increases of the aqueous phase velocity and the lipid concentration, while increased slightly with the increases of the surfactant concentration and the lipid-solvent velocity under the test conditions. The corresponding mechanisms were also analyzed and discussed.