Development and characterization of liposomes containing glycols as carriers for diclofenac

This paper focuses on the preparation and characterization of new, stable phospholipid formulations as carriers for dermal delivery of diclofenac (DCF). To prepare these vesicles two water miscible permeation enhancers (PE) with glycol group: diethyleneglycol monoethyl ether (Transcutol®, Trc) and propylene glycol (PG), were added at different concentrations (10%, 20%, 30%, 40%, 50%) during the preparation of diclofenac loaded soy lecithin (SL) liposomes. We added Transcutol® or propylene glycol to the hydrophilic phase in order to obtain new systems able to enhance the skin delivery of diclofenac thanks to the synergic effect of glycols and phospholipids. Permeation enhancing vesicles (PEVs) were characterised by means of transmission electron microscopy (TEM), zeta potential, entrapment efficiency (E%) and reological properties. TEM micrographies showed that vesicle morphology was irregular and an ovoidal shape was predominant. Vesicular size decreased in the presence of Transcutol® (up to 20%) and propylene glycol (from 10% to 50%). E% increased in vesicles prepared with 10% and 20% of Trc with respect to SL liposomes and PEVs containing the same amount of PG. Vesicle dispersions were slowly frozen and unfrozen to break the vesicle bilayer and the rheological measurements of defrosted samples were carried out without stirring to avoid vesicle reconstitution. The shear stress values were measured for a given rate of shear. Results showed that the presence of Trc or PG in vesicle dispersions facilitated the vesicle segregation from lamellar phase allowing a reduction of hysteresis loop area and apparent viscosity.