µEs were obtained with biocompatible GRAS ingredients (Generally Recognized As Safe). Among different lipids tested (TL, trimyristin, tristearin, myristic acid, glyceryl dibehenate, and glyceryl monostearate), a TL solution in EA was chosen as oil phase, because of its highest solubility in this partially water-miscible solvent (
Epikuron® 200 was chosen as surfactant together with polysorbate (20, 40, 80) or Cremophor® RH 60 at 3:1 w/w constant ratio.
Na TdC, Na TC, Na GC, Na C were tested as co-surfactants, BenzOH was chosen as a co-solvent.
A formulation study was performed varying the percentages of surfactant and co-surfactant/co-solvent. The optimal µE formulation, in the absence of any drug, called µE1, is reported in
µE1 (1 mL) was then diluted with a 2% w/w polymeric aqueous solution (5 mL) to precipitate SLNs. In order to avoid SLN aggregation [16 (link)], different polymers (Cremophor® RH60, Pluronic® F68, PVA® 9000, PVA® 14000) and different percentages of Pluronic® F68 were tested to check the best conditions to obtain small and non-aggregated SLNs. Probably, the polymer disposition on SLN surface influences surface hydrophilicity and charge. A formulation study was then performed to optimize SLN size.